diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
index f928e0156..cfb01b59e 100644
--- a/.github/workflows/docs.yml
+++ b/.github/workflows/docs.yml
@@ -47,6 +47,18 @@ jobs:
           make doc
           popd
 
+      - name: preview
+        uses: afc163/surge-preview@v1
+        id: preview_step
+        with:
+          surge_token: ${{ secrets.SURGE_TOKEN }}
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          dist: docs/_build/html
+          build: echo "done"
+
+      - name: Get the preview_url
+        run: echo "url => ${{ steps.preview_step.outputs.preview_url }}"
+
       - name: Commit Doc
         if: ${{ github.ref == 'refs/heads/main' && github.repository == 'alibaba/GraphAr' }}
         run: |
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0a11dc989..9ddcd217e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -194,7 +194,7 @@ build_gar()
 
 # ------------------------------------------------------------------------------
 # build example
-# ------------------------------------------------------------------------------ 
+# ------------------------------------------------------------------------------
 if (BUILD_EXAMPLES)
     find_package(Boost REQUIRED COMPONENTS graph)
 
@@ -305,6 +305,8 @@ if(doxygen_EXECUTABLE AND sphinx_build_EXECUTABLE)
         COMMAND ${CMAKE_COMMAND} -E make_directory _build
         COMMAND ${doxygen_EXECUTABLE}
         COMMAND ${sphinx_build_EXECUTABLE} . _build/html
+        COMMAND cd ../spark && mvn scala:doc && rm -fr ${PROJECT_SOURCE_DIR}/docs/_build/html/reference/spark-api &&
+         cp -fr target/site/scaladocs ${PROJECT_SOURCE_DIR}/docs/_build/html/reference/spark-api
         WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}/docs
         VERBATIM
     )
diff --git a/docs/index.rst b/docs/index.rst
index b0d849898..b9a5c689b 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -34,6 +34,6 @@
 .. toctree::
    :maxdepth: 1
    :caption: API Reference
-   :hidden:
 
-   api-reference.rst
+   reference/api-reference-cpp.rst
+   Spark tool API Reference <reference/spark-api/index>
diff --git a/docs/api-reference.rst b/docs/reference/api-reference-cpp.rst
similarity index 99%
rename from docs/api-reference.rst
rename to docs/reference/api-reference-cpp.rst
index dbe83f947..5b11dc4f6 100644
--- a/docs/api-reference.rst
+++ b/docs/reference/api-reference-cpp.rst
@@ -1,4 +1,4 @@
-API Reference
+C++ API Reference
 ==============
 
 .. _cpp-api:
diff --git a/docs/reference/spark-api/index.rst b/docs/reference/spark-api/index.rst
new file mode 100644
index 000000000..34ef83117
--- /dev/null
+++ b/docs/reference/spark-api/index.rst
@@ -0,0 +1,4 @@
+Spark API Reference (javadoc)
+========================
+
+Stub page for the Java reference docs; actual source is located in the spark-api/ directory.
\ No newline at end of file
diff --git a/include/gar/graph_info.h b/include/gar/graph_info.h
index 8683809c8..476f98831 100644
--- a/include/gar/graph_info.h
+++ b/include/gar/graph_info.h
@@ -504,7 +504,7 @@ class EdgeInfo {
   }
 
   /**
-   * @brief Return property group that contains certain property and with adj
+   * @brief Return property group that contains property and with adj
    * list type
    *
    * @param property property name
diff --git a/include/gar/reader/arrow_chunk_reader.h b/include/gar/reader/arrow_chunk_reader.h
index ce69447b0..914e65d54 100644
--- a/include/gar/reader/arrow_chunk_reader.h
+++ b/include/gar/reader/arrow_chunk_reader.h
@@ -141,7 +141,7 @@ class AdjListArrowChunkReader {
    * @brief Initialize the AdjListArrowChunkReader.
    *
    * @param edge_info The edge info that describes the edge type.
-   * @param adj_list_type The adj list type for the edges.
+   * @param adj_list_type The adj list type for the edge.
    * @param prefix The absolute prefix.
    * @param vertex_chunk_index The vertex chunk index, default is 0.
    */
diff --git a/include/gar/utils/data_type.h b/include/gar/utils/data_type.h
index 4ee9b5dcb..9cf7cb987 100644
--- a/include/gar/utils/data_type.h
+++ b/include/gar/utils/data_type.h
@@ -32,13 +32,13 @@ namespace GAR_NAMESPACE_INTERNAL {
 
 /// \brief Main data type enumeration
 enum class Type {
-  /// Boolean as 1 bit, LSB bit-packed ordering
+  /// Boolean
   BOOL = 0,
 
-  /// Signed 32-bit little-endian integer
+  /// Signed 32-bit integer
   INT32,
 
-  /// Signed 64-bit little-endian integer
+  /// Signed 64-bit integer
   INT64,
 
   /// 4-byte floating point value
@@ -47,7 +47,7 @@ enum class Type {
   /// 8-byte floating point value
   DOUBLE,
 
-  /// UTF8 variable-length string as List<Char>
+  /// UTF8 variable-length string
   STRING,
 
   /// User-defined data type
diff --git a/spark/pom.xml b/spark/pom.xml
index 8d69d3a15..d350582a8 100644
--- a/spark/pom.xml
+++ b/spark/pom.xml
@@ -189,6 +189,17 @@
                     </execution>
                 </executions>
             </plugin>
+            <plugin>
+                <groupId>net.alchim31.maven</groupId>
+                <artifactId>scala-maven-plugin</artifactId>
+                <version>4.8.0</version>
+                <configuration>
+                    <jvmArgs>
+                        <jvmArg>-Xms64m</jvmArg>
+                        <jvmArg>-Xmx1024m</jvmArg>
+                    </jvmArgs>
+                </configuration>
+            </plugin>
         </plugins>
     </build>
     <packaging>jar</packaging>
diff --git a/spark/src/main/java/com/alibaba/graphar/GeneralParams.java b/spark/src/main/java/com/alibaba/graphar/GeneralParams.java
index 6c8868199..0ba691e2a 100644
--- a/spark/src/main/java/com/alibaba/graphar/GeneralParams.java
+++ b/spark/src/main/java/com/alibaba/graphar/GeneralParams.java
@@ -15,6 +15,7 @@
 
 package com.alibaba.graphar;
 
+/** General constant parameters for graphar. */
 public class GeneralParams {
     // column name
     public static final String vertexIndexCol = "_graphArVertexIndex";
diff --git a/spark/src/main/scala/com/alibaba/graphar/EdgeInfo.scala b/spark/src/main/scala/com/alibaba/graphar/EdgeInfo.scala
index bddd4ee09..bb48a30ea 100644
--- a/spark/src/main/scala/com/alibaba/graphar/EdgeInfo.scala
+++ b/spark/src/main/scala/com/alibaba/graphar/EdgeInfo.scala
@@ -20,6 +20,7 @@ import org.yaml.snakeyaml.Yaml
 import org.yaml.snakeyaml.constructor.Constructor
 import scala.beans.BeanProperty
 
+/** Edge info is a class to store the edge meta information. */
 class EdgeInfo() {
   @BeanProperty var src_label: String = ""
   @BeanProperty var edge_label: String = ""
@@ -32,6 +33,11 @@ class EdgeInfo() {
   @BeanProperty var adj_lists = new java.util.ArrayList[AdjList]()
   @BeanProperty var version: String = ""
 
+  /** Check if the edge info supports the adj list type.
+   *
+   * @param adj_list_type adjList type in gar to check.
+   * @return true if edge info supports the adj list type, otherwise return false.
+   */
   def containAdjList(adj_list_type: AdjListType.Value): Boolean = {
     val tot: Int = adj_lists.size
     for ( k <- 0 to tot - 1 ) {
@@ -42,6 +48,12 @@ class EdgeInfo() {
     return false
   }
 
+  /** Get path prefix of adj list type.
+   *
+   * @param adj_list_type The input adj list type in gar.
+   * @return path prefix of the adj list type, if edge info not support the adj list type,
+   *         raise an IllegalArgumentException error.
+   */
   def getAdjListPrefix(adj_list_type: AdjListType.Value): String = {
     val tot: Int = adj_lists.size
     for ( k <- 0 to tot - 1 ) {
@@ -57,6 +69,12 @@ class EdgeInfo() {
     throw new IllegalArgumentException
   }
 
+  /** Get the adj list topology chunk file type of adj list type.
+   *
+   * @param adj_list_type the input adj list type.
+   * @return file format tupe in gar of the adj list type, if edge info not support the adj list type,
+   *         raise an IllegalArgumentException error.
+   */
   def getAdjListFileType(adj_list_type: AdjListType.Value): FileType.Value = {
     val tot: Int = adj_lists.size
     for ( k <- 0 to tot - 1 ) {
@@ -68,6 +86,12 @@ class EdgeInfo() {
     throw new IllegalArgumentException
   }
 
+  /** Get the property groups of adj list type.
+   *
+   * @param adj_list_type the input adj list type.
+   * @return property group of the input adj list type, if edge info not support the adj list type,
+   *         raise an IllegalArgumentException error.
+   */
   def getPropertyGroups(adj_list_type: AdjListType.Value): java.util.ArrayList[PropertyGroup] = {
     val tot: Int = adj_lists.size
     for ( k <- 0 to tot - 1 ) {
@@ -79,6 +103,14 @@ class EdgeInfo() {
     throw new IllegalArgumentException
   }
 
+  /** Check if the edge info contains the property group in cerain adj list structure.
+   *
+   * @param property_group the property group to check.
+   * @param adj_list_type the type of adj list structure.
+   * @return true if the edge info contains the property group in cerain adj list structure.
+   *         If edge info not support the given adj list type or not contains the proerpty group in the adj list structure,
+   *         return false.
+   */
   def containPropertyGroup(property_group: PropertyGroup, adj_list_type: AdjListType.Value): Boolean = {
     val tot: Int = adj_lists.size
     for ( k <- 0 to tot - 1 ) {
@@ -97,6 +129,11 @@ class EdgeInfo() {
     return false
   }
 
+  /**  Check if the edge info contains the property.
+   *
+   * @param property_name name of the property.
+   * @return true if edge info contains the property, otherwise false.
+   */
   def containProperty(property_name: String): Boolean = {
     val tot: Int = adj_lists.size
     for ( k <- 0 to tot - 1 ) {
@@ -117,6 +154,13 @@ class EdgeInfo() {
     return false
   }
 
+  /** Get property group that contains property with adj list type.
+   *
+   * @param property_name name of the property.
+   * @param adj_list_type the type of adj list structure.
+   * @return property group that contains the property. If edge info not support the adj list type,
+   *         or not find the property group that contains the property, return false.
+   */
   def getPropertyGroup(property_name: String, adj_list_type: AdjListType.Value): PropertyGroup = {
     val tot: Int = adj_lists.size
     for ( k <- 0 to tot - 1 ) {
@@ -139,6 +183,12 @@ class EdgeInfo() {
     throw new IllegalArgumentException
   }
 
+  /** Get the data type of property.
+   *
+   * @param property_name name of the property.
+   * @return data type in gar of the property. If edge info not contains the property,
+   *         raise an IllegalArgumentException error.
+   */
   def getPropertyType(property_name: String): GarType.Value = {
     val tot: Int = adj_lists.size
     for ( k <- 0 to tot - 1 ) {
@@ -159,6 +209,12 @@ class EdgeInfo() {
     throw new IllegalArgumentException
   }
 
+  /** Check the property is primary key of edge info.
+   *
+   * @param property_name name of the property.
+   * @return true if the property is the primary key of edge info, false if not.
+   *         If edge info not contains the property, raise an IllegalArgumentException error.
+   */
   def isPrimaryKey(property_name: String): Boolean = {
     val tot: Int = adj_lists.size
     for ( k <- 0 to tot - 1 ) {
@@ -179,6 +235,7 @@ class EdgeInfo() {
     throw new IllegalArgumentException
   }
 
+  /** Get Primary key of edge info. */
   def getPrimaryKey(): String = {
     val tot: Int = adj_lists.size
     for ( k <- 0 to tot - 1 ) {
@@ -199,6 +256,7 @@ class EdgeInfo() {
     return ""
   }
 
+  /** Check if the edge info is validated. */
   def isValidated(): Boolean = {
     if (src_label == "" || edge_label == "" || dst_label == "")
       return false
@@ -222,6 +280,14 @@ class EdgeInfo() {
     return true
   }
 
+  /** Get the adj list offset chunk file path of vertex chunk
+   *  the offset chunks is aligned with the vertex chunks
+   *
+   *  @param chunk_inde index of vertex chunk.
+   *  @param adj_list_type type of adj list structure.
+   *  @return the offset chunk file path. If edge info not support the adj list type,
+   *          raise an IllegalArgumentException error.
+   */
   def getAdjListOffsetFilePath(chunk_index: Long, adj_list_type: AdjListType.Value) : String = {
     if (containAdjList(adj_list_type) == false)
       throw new IllegalArgumentException
@@ -230,28 +296,63 @@ class EdgeInfo() {
     return str
   }
 
+  /** Get the adj list offset chunk file directory path of adj list type.
+   *
+   * @param adj_list_type type of adj list structure.
+   * @return the offset directory. If edge info not support the adj list type,
+   *          raise an IllegalArgumentException error.
+   */
   def getAdjListOffsetDirPath(adj_list_type: AdjListType.Value) : String = {
     if (containAdjList(adj_list_type) == false)
       throw new IllegalArgumentException
     return prefix + getAdjListPrefix(adj_list_type) + "offset/"
   }
 
+  /** Get the file path of adj list topology chunk.
+   *
+   * @param vertex_chunk_index index of vertex chunk.
+   * @param chunk_index index of edge chunk.
+   * @param adj_list_type type of adj list structure.
+   * @return adj list chunk file path.
+   */
   def getAdjListFilePath(vertex_chunk_index: Long, chunk_index: Long, adj_list_type: AdjListType.Value) : String = {
     var str: String = prefix + getAdjListPrefix(adj_list_type) + "adj_list/part" +
         vertex_chunk_index.toString() + "/chunk" + chunk_index.toString()
     return str
   }
 
+  /** Get the path of adj list topology chunk of certain vertex chunk.
+   *
+   * @param vertex_chunk_index index of vertex chunk.
+   * @param adj_list_type type of adj list structure.
+   * @return path prefix of the edge chunk of vertices of given vertex chunk.
+   */
   def getAdjListFilePath(vertex_chunk_index: Long, adj_list_type: AdjListType.Value) : String = {
     var str: String = prefix + getAdjListPrefix(adj_list_type) + "adj_list/part" +
       vertex_chunk_index.toString() + "/"
     return str
   }
 
+  /** Get the adj list topology chunk file directory path of adj list type.
+   *
+   * @param adj_list_type type of adj list structure.
+   * @return directory path of adj list type.
+   */
   def getAdjListDirPath(adj_list_type: AdjListType.Value) : String = {
     return prefix + getAdjListPrefix(adj_list_type) + "adj_list/"
   }
 
+  /** Get the chunk file path of adj list property group.
+   *  the property group chunks is aligned with the adj list topology chunks
+   *
+   * @param property_group property group
+   * @param adj_list_type type of adj list structure.
+   * @param vertex_chunk_index index of vertex chunk.
+   * @param chunk_index index of edge chunk.
+   *
+   * @return property group chunk file path. If edge info not contains the property group,
+   *         raise an IllegalArgumentException error.
+   */
   def getPropertyFilePath(property_group: PropertyGroup, adj_list_type: AdjListType.Value, vertex_chunk_index: Long, chunk_index: Long) : String = {
     if (containPropertyGroup(property_group, adj_list_type) == false)
       throw new IllegalArgumentException
@@ -271,6 +372,15 @@ class EdgeInfo() {
     return str
   }
 
+  /** Get path of adj list property group of certain vertex chunk.
+   *
+   * @param property_group property group.
+   * @param adj_list_type type of adj list structure.
+   * @param vertex_chunk_index index of vertex chunk.
+   * @return path prefix of property group chunks of of vertices of given vertex chunk.
+   *         If edge info not contains the property group,
+   *         raise an IllegalArgumentException error.
+   */
   def getPropertyFilePath(property_group: PropertyGroup, adj_list_type: AdjListType.Value, vertex_chunk_index: Long) : String = {
     if (containPropertyGroup(property_group, adj_list_type) == false)
       throw new IllegalArgumentException
@@ -290,6 +400,13 @@ class EdgeInfo() {
     return str
   }
 
+  /** Get the property group chunk file directory path of adj list type.
+   *
+   * @param property_group property group.
+   * @param adj_list_type type of adj list structure.
+   * @return directory path of property group chunks. If edge info not contains the property group,
+   *         raise an IllegalArgumentException error.
+   */
   def getPropertyDirPath(property_group: PropertyGroup, adj_list_type: AdjListType.Value) : String = {
     if (containPropertyGroup(property_group, adj_list_type) == false)
       throw new IllegalArgumentException
diff --git a/spark/src/main/scala/com/alibaba/graphar/GraphInfo.scala b/spark/src/main/scala/com/alibaba/graphar/GraphInfo.scala
index 52ad38c66..906086f6c 100644
--- a/spark/src/main/scala/com/alibaba/graphar/GraphInfo.scala
+++ b/spark/src/main/scala/com/alibaba/graphar/GraphInfo.scala
@@ -20,15 +20,28 @@ import org.yaml.snakeyaml.Yaml
 import org.yaml.snakeyaml.constructor.Constructor
 import scala.beans.BeanProperty
 
+/** Main data type in gar enumeration */
 object GarType extends Enumeration{
   type GarType = Value
+  /** Boolean type */
   val BOOL = Value(0)
+  /** Signed 32-bit integer */
   val INT32 = Value(2)
+  /** Signed 64-bit integer */
   val INT64 = Value(3)
+  /** 4-byte floating point value */
   val FLOAT = Value(4)
+  /** 8-byte floating point value */
   val DOUBLE = Value(5)
+  /** UTF8 variable-length string */
   val STRING = Value(6)
 
+  /** Data type in gar to string.
+   *
+   * @param gar_type gar data type
+   * @return string name of gar data type.
+   *
+   */
   def GarTypeToString(gar_type: GarType.Value): String = gar_type match {
     case GarType.BOOL => "bool"
     case GarType.INT32 => "int32"
@@ -39,6 +52,12 @@ object GarType extends Enumeration{
     case _ => throw new IllegalArgumentException
   }
 
+  /** String name to data type in gar.
+   *
+   * @param str the string name of gar data type
+   * @return gar data type.
+   *
+   */
   def StringToGarType(str: String): GarType.Value = str match {
     case "bool" => GarType.BOOL
     case "int32" => GarType.INT32
@@ -50,12 +69,19 @@ object GarType extends Enumeration{
   }
 }
 
+/** Type of  file format. */
 object FileType extends Enumeration {
   type FileType = Value
   val CSV = Value(0)
   val PARQUET = Value(1)
   val ORC = Value(2)
 
+  /** File type to string.
+   *
+   * @param file_type  file type in gar
+   * @return string name of file type.
+   *
+   */
   def FileTypeToString(file_type: FileType.Value): String = file_type match {
     case FileType.CSV => "csv"
     case FileType.PARQUET => "parquet"
@@ -63,6 +89,12 @@ object FileType extends Enumeration {
     case _ => throw new IllegalArgumentException
   }
 
+  /** String to file type.
+   *
+   * @param str the string name of file type
+   * @return file type in gar.
+   *
+   */
   def StringToFileType(str: String): FileType.Value = str match {
     case "csv" => FileType.CSV
     case "parquet" => FileType.PARQUET
@@ -72,13 +104,19 @@ object FileType extends Enumeration {
 
 }
 
+/** Adj list type enumeration for adjacency list of graph. */
 object AdjListType extends Enumeration {
   type AdjListType = Value
+  /** collection of edges by source, but unordered, can represent COO format */
   val unordered_by_source = Value(0)
+  /** collection of edges by destination, but unordered, can represent COO format */
   val unordered_by_dest = Value(1)
+  /** collection of edges by source, ordered by source, can represent CSR format */
   val ordered_by_source = Value(2)
+  /** collection of edges by destination, ordered by destination, can represent CSC format */
   val ordered_by_dest = Value(3)
 
+  /** adjList type in gar to string */
   def AdjListTypeToString(adjList_type: AdjListType.Value): String = adjList_type match {
     case AdjListType.unordered_by_source => "unordered_by_source"
     case AdjListType.unordered_by_dest => "unordered_by_dest"
@@ -87,6 +125,7 @@ object AdjListType extends Enumeration {
     case _ => throw new IllegalArgumentException
   }
 
+  /** String to adjList type in gar */
   def StringToAdjListType(str: String): AdjListType.Value = str match {
     case "unordered_by_source" => AdjListType.unordered_by_source
     case "unordered_by_dest" => AdjListType.unordered_by_dest
@@ -96,26 +135,31 @@ object AdjListType extends Enumeration {
   }
 }
 
+/** The property information of vertex or edge. */
 class Property () {
   @BeanProperty var name: String = ""
   @BeanProperty var data_type: String = ""
   @BeanProperty var is_primary: Boolean = false
 
+  /** Get data type in gar of the property */
   def getData_type_in_gar: GarType.Value = {
     GarType.StringToGarType(data_type)
   }
 }
 
+/** PropertyGroup is a class to store the property group information. */
 class PropertyGroup () {
   @BeanProperty var prefix: String = ""
   @BeanProperty var file_type: String = ""
   @BeanProperty var properties = new java.util.ArrayList[Property]()
 
+  /** Get file type in gar of property group */
   def getFile_type_in_gar: FileType.Value = {
     FileType.StringToFileType(file_type)
   }
 }
 
+/** AdjList is a class to store the adj list information of edge. */
 class AdjList () {
   @BeanProperty var ordered: Boolean = false
   @BeanProperty var aligned_by: String = "src"
@@ -123,10 +167,12 @@ class AdjList () {
   @BeanProperty var file_type: String = ""
   @BeanProperty var property_groups = new java.util.ArrayList[PropertyGroup]()
 
+  /** Get file type in gar of adj list */
   def getFile_type_in_gar: FileType.Value = {
     FileType.StringToFileType(file_type)
   }
 
+  /** Get adj list type in string*/
   def getAdjList_type: String = {
     var str: String = ""
     if (ordered) {
@@ -142,11 +188,13 @@ class AdjList () {
     return str
   }
 
+  /** Get adj list type in gar */
   def getAdjList_type_in_gar: AdjListType.Value = {
     AdjListType.StringToAdjListType(getAdjList_type)
   }
 }
 
+/** GraphInfo is is a class to store the graph meta information. */
 class GraphInfo() {
   @BeanProperty var name: String = ""
   @BeanProperty var prefix: String = ""
diff --git a/spark/src/main/scala/com/alibaba/graphar/VertexInfo.scala b/spark/src/main/scala/com/alibaba/graphar/VertexInfo.scala
index 225f4999e..ecf9d80b1 100644
--- a/spark/src/main/scala/com/alibaba/graphar/VertexInfo.scala
+++ b/spark/src/main/scala/com/alibaba/graphar/VertexInfo.scala
@@ -20,6 +20,7 @@ import org.yaml.snakeyaml.Yaml
 import org.yaml.snakeyaml.constructor.Constructor
 import scala.beans.BeanProperty
 
+/** VertexInfo is a class to store the vertex meta information. */
 class VertexInfo() {
   @BeanProperty var label: String = ""
   @BeanProperty var chunk_size: Long = 0
@@ -27,6 +28,11 @@ class VertexInfo() {
   @BeanProperty var property_groups = new java.util.ArrayList[PropertyGroup]()
   @BeanProperty var version: String = ""
 
+  /** Check if the vertex info contains the property group.
+   *
+   * @param property_group the property group to check.
+   * @return true if the vertex info contains the property group, otherwise false.
+   */
   def containPropertyGroup(property_group: PropertyGroup): Boolean = {
     val len: Int = property_groups.size
     for ( i <- 0 to len - 1 ) {
@@ -38,6 +44,11 @@ class VertexInfo() {
     return false
   }
 
+  /** Check if the vertex info contains certain property.
+   *
+   * @param property_name name of the property.
+   * @return true if the vertex info contains the property, otherwise false.
+   */
   def containProperty(property_name: String): Boolean = {
     val len: Int = property_groups.size
     for ( i <- 0 to len - 1 ) {
@@ -53,6 +64,11 @@ class VertexInfo() {
     return false
   }
 
+  /** Get the property group that contains property.
+   *
+   * @param property_name name of the property.
+   * @return property group that contains the property, otherwise raise IllegalArgumentException error.
+   */
   def getPropertyGroup(property_name: String): PropertyGroup = {
     val len: Int = property_groups.size
     for ( i <- 0 to len - 1 ) {
@@ -68,6 +84,12 @@ class VertexInfo() {
     throw new IllegalArgumentException
   }
 
+  /** Get the data type of property.
+   *
+   * @param property_name name of the property.
+   * @return the data type in gar of the proeprty. If the vertex info does not contains the property,
+   *         raise IllegalArgumentException error.
+   */
   def getPropertyType(property_name: String): GarType.Value = {
     val len: Int = property_groups.size
     for ( i <- 0 to len - 1 ) {
@@ -83,6 +105,11 @@ class VertexInfo() {
     throw new IllegalArgumentException
   }
 
+  /** Check if the property is primary key.
+   *
+   * @param property_name name of the property to check.
+   * @return true if the property if the primary key of vertex info, otherwise return false.
+   */
   def isPrimaryKey(property_name: String): Boolean = {
     val len: Int = property_groups.size
     for ( i <- 0 to len - 1 ) {
@@ -98,6 +125,10 @@ class VertexInfo() {
     throw new IllegalArgumentException
   }
 
+  /** Get primary key of vertex info.
+   *
+   * @return name of the primary key.
+   */
   def getPrimaryKey(): String = {
     val len: Int = property_groups.size
     for ( i <- 0 to len - 1 ) {
@@ -113,6 +144,10 @@ class VertexInfo() {
     return ""
   }
 
+  /** Check if the vertex info is validated.
+   *
+   * @return true if the vertex info is validated, otherwise return false.
+   */
  def isValidated(): Boolean = {
     if (label == "" || chunk_size <= 0)
       return false
@@ -128,10 +163,17 @@ class VertexInfo() {
     return true
   }
 
+  /** Get the vertex num file path of vertex info. */
   def getVerticesNumFilePath(): String = {
     return prefix + "vertex_count"
   }
 
+  /** Get the chunk file path of property group of vertex chunk.
+   *
+   * @param property_group the property group.
+   * @param chunk_index the index of vertex chunk
+   * @return chunk file path.
+   */
   def getFilePath(property_group: PropertyGroup, chunk_index: Long): String = {
     if (containPropertyGroup(property_group) == false)
       throw new IllegalArgumentException
@@ -151,6 +193,11 @@ class VertexInfo() {
     return prefix + str + "chunk" + chunk_index.toString()
   }
 
+  /** Get the chunk files directory path of property group.
+   *
+   * @param property_group the property group.
+   * @return the dirctory path that store the chunk files of property group.
+   */
   def getDirPath(property_group: PropertyGroup): String = {
     if (containPropertyGroup(property_group) == false)
       throw new IllegalArgumentException
diff --git a/spark/src/main/scala/com/alibaba/graphar/reader/EdgeReader.scala b/spark/src/main/scala/com/alibaba/graphar/reader/EdgeReader.scala
index 4e3b2dcde..8a9ce0b62 100644
--- a/spark/src/main/scala/com/alibaba/graphar/reader/EdgeReader.scala
+++ b/spark/src/main/scala/com/alibaba/graphar/reader/EdgeReader.scala
@@ -23,11 +23,25 @@ import org.apache.spark.sql.{DataFrame, SparkSession}
 import org.apache.spark.sql.types._
 import org.apache.spark.sql.functions._
 
-class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.Value,spark:SparkSession) {
-  // load a single offset chunk as a DataFrame
+/** Reader for edge chunks.
+ *
+ * @constructor create a new edge reader with edge info and AdjList type.
+ * @param prefix the absolute perfix.
+ * @param edgeInfo the edge info that describes the edge type.
+ * @param adjListType the adj list type for the edge.
+ * @param spark spark session for the reader to read chunks as Spark DataFrame.
+ */
+class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.Value, spark:SparkSession) {
+  if (edgeInfo.containAdjList(adjListType) == false) {
+    throw new IllegalArgumentException
+  }
+
+  /** Load a single offset chunk as a DataFrame.
+   *
+   * @param chunk_index index of offset chunk
+   * @return offset chunk DataFrame.
+   */
   def readOffset(chunk_index: Long): DataFrame = {
-    if (edgeInfo.containAdjList(adjListType) == false)
-      throw new IllegalArgumentException
     if (adjListType != AdjListType.ordered_by_source && adjListType != AdjListType.ordered_by_dest)
       throw new IllegalArgumentException
     val file_type_in_gar = edgeInfo.getAdjListFileType(adjListType)
@@ -37,10 +51,13 @@ class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     return df
   }
 
-  // load a single AdjList chunk as a DataFrame
+  /** Load a single AdjList chunk as a DataFrame.
+   *
+   * @param vertex_chunk_index index of vertex chunk
+   * @param chunk_index index of AdjList chunk.
+   * @return AdjList chunk DataFrame
+   */
   def readAdjListChunk(vertex_chunk_index: Long, chunk_index: Long): DataFrame = {
-    if (edgeInfo.containAdjList(adjListType) == false)
-      throw new IllegalArgumentException
     val file_type_in_gar = edgeInfo.getAdjListFileType(adjListType)
     val file_type = FileType.FileTypeToString(file_type_in_gar)
     val file_path = prefix + "/" + edgeInfo.getAdjListFilePath(vertex_chunk_index, chunk_index, adjListType)
@@ -48,10 +65,13 @@ class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     return df
   }
 
-  // load all AdjList chunks for a vertex chunk as a DataFrame
+  /** Load all AdjList chunks for a vertex chunk as a DataFrame.
+   *
+   * @param vertex_chunk_index index of vertex chunk.
+   * @param addIndex flag that add edge index column or not in the final DataFrame.
+   * @return DataFrame of all AdjList chunks of vertices in given vertex chunk.
+   */
   def readAdjListForVertexChunk(vertex_chunk_index: Long, addIndex: Boolean = false): DataFrame = {
-    if (edgeInfo.containAdjList(adjListType) == false)
-      throw new IllegalArgumentException
     val file_path = prefix + "/" + edgeInfo.getAdjListFilePath(vertex_chunk_index, adjListType)
     val file_system = FileSystem.get(new Path(file_path).toUri(), spark.sparkContext.hadoopConfiguration)
     val path_pattern = new Path(file_path + "chunk*")
@@ -69,10 +89,12 @@ class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     return df
   }
 
-  // load all AdjList chunks for this edge type as a DataFrame
+  /** Load all AdjList chunks for this edge type as a DataFrame.
+   *
+   * @param addIndex flag that add index column or not in the final DataFrame.
+   * @return DataFrame of all AdjList chunks.
+   */
   def readAllAdjList(addIndex: Boolean = false): DataFrame = {
-    if (edgeInfo.containAdjList(adjListType) == false)
-      throw new IllegalArgumentException
     val file_path = prefix + "/" + edgeInfo.getAdjListDirPath(adjListType)
     val file_system = FileSystem.get(new Path(file_path).toUri(), spark.sparkContext.hadoopConfiguration)
     val path_pattern = new Path(file_path + "part*")
@@ -90,10 +112,15 @@ class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     return df
   }
 
-  // load a single edge property chunk as a DataFrame
+  /** Load a single edge property chunk as a DataFrame.
+   *
+   * @param propertyGroup property group.
+   * @param vertex_chunk_index index of vertex chunk.
+   * @param chunk_index index of property group chunk.
+   * @return property group chunk DataFrame. If edge info does not contain the property group,
+   *         raise an IllegalArgumentException error.
+   */
   def readEdgePropertyChunk(propertyGroup: PropertyGroup, vertex_chunk_index: Long, chunk_index: Long): DataFrame = {
-    if (edgeInfo.containAdjList(adjListType) == false)
-      throw new IllegalArgumentException
     if (edgeInfo.containPropertyGroup(propertyGroup, adjListType) == false)
       throw new IllegalArgumentException
     val file_type = propertyGroup.getFile_type();
@@ -102,10 +129,15 @@ class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     return df
   }
 
-  // load the chunks for a property group of a vertex chunk as a DataFrame
+  /** Load the chunks for a property group of a vertex chunk as a DataFrame.
+   *
+   * @param propertyGroup property group.
+   * @param vertex_chunk_index index of vertex chunk.
+   * @param addIndex  flag that add edge index column or not in the final DataFrame.
+   * @return DataFrame that contains all property group chunks of vertices in given vertex chunk.
+   *         If edge info does not contain the property group, raise an IllegalArgumentException error.
+   */
   def readEdgePropertiesForVertexChunk(propertyGroup: PropertyGroup, vertex_chunk_index: Long, addIndex: Boolean = false): DataFrame = {
-    if (edgeInfo.containAdjList(adjListType) == false)
-      throw new IllegalArgumentException
     if (edgeInfo.containPropertyGroup(propertyGroup, adjListType) == false)
       throw new IllegalArgumentException
     val file_path = prefix + "/" + edgeInfo.getPropertyFilePath(propertyGroup, adjListType, vertex_chunk_index)
@@ -125,10 +157,14 @@ class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     return df
   }
 
-  // load all chunks for a property group as a DataFrame
+  /** Load all chunks for a property group as a DataFrame.
+   *
+   * @param propertyGroup property group.
+   * @param addIndex flag that add edge index column or not in the final DataFrame.
+   * @return DataFrame that contains all chunks of property group.
+   *         If edge info does not contain the property group, raise an IllegalArgumentException error.
+   */
   def readEdgeProperties(propertyGroup: PropertyGroup, addIndex: Boolean = false): DataFrame = {
-    if (edgeInfo.containAdjList(adjListType) == false)
-      throw new IllegalArgumentException
     if (edgeInfo.containPropertyGroup(propertyGroup, adjListType) == false)
       throw new IllegalArgumentException
     val file_path = prefix + "/" + edgeInfo.getPropertyDirPath(propertyGroup, adjListType)
@@ -148,10 +184,13 @@ class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     return df
   }
 
-  // load the chunks for all property groups of a vertex chunk as a DataFrame
+  /** Load the chunks for all property groups of a vertex chunk as a DataFrame.
+   *
+   * @param vertex_chunk_index index of vertex chunk.
+   * @param addIndex flag that add edge index column or not in the final DataFrame.
+   * @return DataFrame that contains all property groups chunks of a vertex chunk.
+   */
   def readAllEdgePropertiesForVertexChunk(vertex_chunk_index: Long, addIndex: Boolean = false): DataFrame = {
-    if (edgeInfo.containAdjList(adjListType) == false)
-      throw new IllegalArgumentException
     var df = spark.emptyDataFrame
     val property_groups = edgeInfo.getPropertyGroups(adjListType)
     val len: Int = property_groups.size
@@ -168,11 +207,13 @@ class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
       df = df.drop(GeneralParams.edgeIndexCol)
     return df
   }
-  
-  // load the chunks for all property groups as a DataFrame
+
+  /** Load the chunks for all property groups as a DataFrame.
+   *
+   * @param addIndex flag that add edge index column or not in the final DataFrame.
+   * @return DataFrame tha contains all property groups chunks of edge.
+   */
   def readAllEdgeProperties(addIndex: Boolean = false): DataFrame = {
-    if (edgeInfo.containAdjList(adjListType) == false)
-      throw new IllegalArgumentException
     var df = spark.emptyDataFrame
     val property_groups = edgeInfo.getPropertyGroups(adjListType)
     val len: Int = property_groups.size
@@ -190,10 +231,13 @@ class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     return df
   }
 
-  // load the chunks for the AdjList and all property groups for a vertex chunk as a DataFrame
+  /** Load the chunks for the AdjList and all property groups for a vertex chunk as a DataFrame.
+   *
+   * @param vertex_chunk_index index of vertex chunk
+   * @param addIndex flag that add edge index column or not in the final DataFrame.
+   * @return DataFrame that contains all chunks of AdjList and property groups of vertices in given vertex chunk.
+   */
   def readEdgesForVertexChunk(vertex_chunk_index: Long, addIndex: Boolean = false): DataFrame = {
-    if (edgeInfo.containAdjList(adjListType) == false)
-      throw new IllegalArgumentException
     val adjList_df = readAdjListForVertexChunk(vertex_chunk_index, true)
     val properties_df = readAllEdgePropertiesForVertexChunk(vertex_chunk_index, true)
     var df = adjList_df.join(properties_df, Seq(GeneralParams.edgeIndexCol)).sort(GeneralParams.edgeIndexCol)
@@ -202,10 +246,12 @@ class EdgeReader(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     return df
   }
 
-  // load the chunks for the AdjList and all property groups as a DataFrame
+  /** Load the chunks for the AdjList and all property groups as a DataFrame.
+   *
+   * @param addIndex flag that add edge index column or not in the final DataFrame.
+   * @return DataFrame that contains all chunks of AdjList and property groups of edge.
+   */
   def readEdges(addIndex: Boolean = false): DataFrame = {
-    if (edgeInfo.containAdjList(adjListType) == false)
-      throw new IllegalArgumentException
     val adjList_df = readAllAdjList(true)
     val properties_df = readAllEdgeProperties(true)
     var df = adjList_df.join(properties_df, Seq(GeneralParams.edgeIndexCol)).sort(GeneralParams.edgeIndexCol);
diff --git a/spark/src/main/scala/com/alibaba/graphar/reader/VertexReader.scala b/spark/src/main/scala/com/alibaba/graphar/reader/VertexReader.scala
index 7032c1a22..15e2d0c96 100644
--- a/spark/src/main/scala/com/alibaba/graphar/reader/VertexReader.scala
+++ b/spark/src/main/scala/com/alibaba/graphar/reader/VertexReader.scala
@@ -23,6 +23,13 @@ import org.apache.spark.sql.{DataFrame, SparkSession}
 import org.apache.spark.sql.types._
 import org.apache.spark.sql.functions._
 
+/** Reader for vertex chunks.
+ *
+ * @constructor create a new vertex reader with vertex info.
+ * @param prefix the absolute prefix.
+ * @param vertexInfo the vertex info that describes the vertex type.
+ * @param spark spark session for the reader to read chunks as Spark DataFrame.
+ */
 class VertexReader(prefix: String, vertexInfo: VertexInfo, spark: SparkSession) {
   private val vertices_number = readVerticesNumber()
   private val chunk_size = vertexInfo.getChunk_size()
@@ -30,7 +37,7 @@ class VertexReader(prefix: String, vertexInfo: VertexInfo, spark: SparkSession)
   if (vertices_number % chunk_size != 0)
     chunk_number = chunk_number + 1
  
-  // load the total number of vertices for this vertex type
+  /** Load the total number of vertices for this vertex type. */
   def readVerticesNumber(): Long = {
     val file_path = prefix + "/" + vertexInfo.getVerticesNumFilePath()
     val path = new Path(file_path)
@@ -41,7 +48,12 @@ class VertexReader(prefix: String, vertexInfo: VertexInfo, spark: SparkSession)
     return number
   }
 
-  // load a single vertex property chunk as a DataFrame
+  /** Load a single vertex property chunk as a DataFrame.
+   *
+   * @param propertyGroup property group.
+   * @param chunk_index index of vertex chunk.
+   * @return vertex property chunk DataFrame.
+   */
   def readVertexPropertyChunk(propertyGroup: PropertyGroup, chunk_index: Long): DataFrame = {
     if (vertexInfo.containPropertyGroup(propertyGroup) == false) 
       throw new IllegalArgumentException
@@ -51,7 +63,12 @@ class VertexReader(prefix: String, vertexInfo: VertexInfo, spark: SparkSession)
     return df
   }
 
-  // load all chunks for a property group as a DataFrame
+  /** Load all chunks for a property group as a DataFrame.
+   *
+   * @param propertyGroup property group.
+   * @param addIndex flag that add vertex index column or not in the final DataFrame.
+   * @return DataFrame that contains all chunks of property group.
+   */
   def readVertexProperties(propertyGroup: PropertyGroup, addIndex: Boolean = false): DataFrame = {
     if (vertexInfo.containPropertyGroup(propertyGroup) == false) 
       throw new IllegalArgumentException
@@ -68,7 +85,11 @@ class VertexReader(prefix: String, vertexInfo: VertexInfo, spark: SparkSession)
     return df
   }
 
-  // load the chunks for all property groups as a DataFrame
+  /** Load the chunks for all property groups as a DataFrame.
+   *
+   * @param addIndex flag that add vertex index column or not in the final DataFrame.
+   * @return DataFrame that contains all property group chunks of vertex.
+   */
   def readAllVertexProperties(addIndex: Boolean = false): DataFrame = {
     var df = spark.emptyDataFrame
     val property_groups = vertexInfo.getProperty_groups()
diff --git a/spark/src/main/scala/com/alibaba/graphar/utils/FileSystem.scala b/spark/src/main/scala/com/alibaba/graphar/utils/FileSystem.scala
index 2ce28a7d2..45d46961b 100644
--- a/spark/src/main/scala/com/alibaba/graphar/utils/FileSystem.scala
+++ b/spark/src/main/scala/com/alibaba/graphar/utils/FileSystem.scala
@@ -20,6 +20,7 @@ import org.apache.spark.sql.SparkSession
 import org.apache.spark.sql.DataFrame
 import org.apache.hadoop.fs
 
+/** Helper object to write dataframe to chunk files */
 object FileSystem {
   private def renameSparkGeneratedFiles(spark: SparkSession, filePrefix: String): Unit = {
     val sc = spark.sparkContext
@@ -33,6 +34,12 @@ object FileSystem {
     }
   }
 
+  /** Write input dataframe to output path with certain file format.
+   *
+   * @param dataframe DataFrame to write out.
+   * @param fileType output file format type, the value could be csv|parquet|orc.
+   * @param outputPrefix output path prefix.
+   */
   def writeDataFrame(dataFrame: DataFrame, fileType: String, outputPrefix: String): Unit = {
     val spark = dataFrame.sparkSession
     spark.conf.set("mapreduce.fileoutputcommitter.marksuccessfuljobs", "false")
diff --git a/spark/src/main/scala/com/alibaba/graphar/utils/IndexGenerator.scala b/spark/src/main/scala/com/alibaba/graphar/utils/IndexGenerator.scala
index 2e6f594f9..f611794ec 100644
--- a/spark/src/main/scala/com/alibaba/graphar/utils/IndexGenerator.scala
+++ b/spark/src/main/scala/com/alibaba/graphar/utils/IndexGenerator.scala
@@ -27,11 +27,17 @@ import org.apache.spark.rdd.RDD
 import scala.collection.SortedMap
 import scala.collection.mutable.ArrayBuffer
 
+/** IndexGenerator is a object to help to generate the indices for vertex/edge DataFrames. */
 object IndexGenerator {
 
   // index helper for the vertex DataFrame
 
-  // return a DataFrame contains two columns: vertex index & primary key
+  /** Generate a vertex index mapping of primary key.a DataFrame contains two columns: vertex index & primary key
+   *
+   * @param vertexDf  input vertex DataFrame.
+   * @param primaryKey the primary key of vertex
+   * @return a DataFrame contains two columns: vertex index & primary key.
+   */
   def constructVertexIndexMapping(vertexDf: DataFrame, primaryKey: String): DataFrame = {
     val spark = vertexDf.sparkSession
     val schema = vertexDf.schema
@@ -54,7 +60,11 @@ object IndexGenerator {
     spark.createDataFrame(mapping, mapping_schema).withColumnRenamed(primaryKey, GeneralParams.primaryCol)
   }
 
-  //add a column contains vertex index
+  /** Add a column contains vertex index to DataFrame
+   *
+   * @param vertexDf the input vertex DataFrame.
+   * @return DataFrame that contains a new vertex index column.
+   */
   def generateVertexIndexColumn(vertexDf: DataFrame): DataFrame = {
     val spark = vertexDf.sparkSession
     val schema = vertexDf.schema
@@ -76,9 +86,9 @@ object IndexGenerator {
     spark.createDataFrame(rdd_with_index, schema_with_index)
   }
 
-  //index helper for the Edge DataFrame
+  // index helper for the Edge DataFrame
 
-  //add a column contains edge index
+  /** Add a column contains edge index to input edge DataFrame. */
   def generateEdgeIndexColumn(edgeDf: DataFrame): DataFrame = {
     val spark = edgeDf.sparkSession
     val schema = edgeDf.schema
@@ -100,7 +110,7 @@ object IndexGenerator {
     spark.createDataFrame(rdd_with_index, schema_with_index)
   }
 
-  // join the edge table with the vertex index mapping for source column
+  /** Join the edge table with the vertex index mapping for source column. */
   def generateSrcIndexForEdgesFromMapping(edgeDf: DataFrame, srcColumnName: String, srcIndexMapping: DataFrame): DataFrame = {
     val spark = edgeDf.sparkSession
     srcIndexMapping.createOrReplaceTempView("src_vertex")
@@ -113,7 +123,7 @@ object IndexGenerator {
     trans_df.drop(srcColumnName)
 	}
 
-  // join the edge table with the vertex index mapping for destination column
+  /** Join the edge table with the vertex index mapping for destination column. */
   def generateDstIndexForEdgesFromMapping(edgeDf: DataFrame, dstColumnName: String, dstIndexMapping: DataFrame): DataFrame = {
     val spark = edgeDf.sparkSession
     dstIndexMapping.createOrReplaceTempView("dst_vertex")
@@ -126,27 +136,27 @@ object IndexGenerator {
     trans_df.drop(dstColumnName)
 	}
 
-  // join the edge table with the vertex index mapping for source & destination columns
+  /** Join the edge table with the vertex index mapping for source & destination columns. */
   def generateSrcAndDstIndexForEdgesFromMapping(edgeDf: DataFrame, srcColumnName: String, dstColumnName: String, srcIndexMapping: DataFrame, dstIndexMapping: DataFrame): DataFrame = {
     val df_with_src_index = generateSrcIndexForEdgesFromMapping(edgeDf, srcColumnName, srcIndexMapping)
     generateDstIndexForEdgesFromMapping(df_with_src_index, dstColumnName, dstIndexMapping)
 	}
 
-  // construct vertex index for source column
+  /** Construct vertex index for source column. */
   def generateSrcIndexForEdges(edgeDf: DataFrame, srcColumnName: String): DataFrame = {
     val srcDf = edgeDf.select(srcColumnName).distinct()
     val srcIndexMapping = constructVertexIndexMapping(srcDf, srcColumnName)
     generateSrcIndexForEdgesFromMapping(edgeDf, srcColumnName, srcIndexMapping)
 	}
 
-  // construct vertex index for destination column
+  /** Construct vertex index for destination column. */
   def generateDstIndexForEdges(edgeDf: DataFrame, dstColumnName: String): DataFrame = {
     val dstDf = edgeDf.select(dstColumnName).distinct()
     val dstIndexMapping = constructVertexIndexMapping(dstDf, dstColumnName)
     generateDstIndexForEdgesFromMapping(edgeDf, dstColumnName, dstIndexMapping)
 	}
 
-  // union and construct vertex index for source & destination columns
+  /** Union and construct vertex index for source & destination columns. */
   def generateSrcAndDstIndexUnitedlyForEdges(edgeDf: DataFrame, srcColumnName: String, dstColumnName: String): DataFrame = {
     val srcDf = edgeDf.select(srcColumnName)
     val dstDf = edgeDf.select(dstColumnName)
diff --git a/spark/src/main/scala/com/alibaba/graphar/utils/Patitioner.scala b/spark/src/main/scala/com/alibaba/graphar/utils/Patitioner.scala
index 7d68a7ef0..614289efc 100644
--- a/spark/src/main/scala/com/alibaba/graphar/utils/Patitioner.scala
+++ b/spark/src/main/scala/com/alibaba/graphar/utils/Patitioner.scala
@@ -18,7 +18,13 @@ package com.alibaba.graphar.utils
 import org.apache.spark.sql.types._
 import org.apache.spark.Partitioner
 
-
+/** Partioner for vertex/edge DataFrame to partition by chunk size.
+ *
+ * @constructor create a new chunk partitioner
+ * @param partitions partition num.
+ * @chunk_size size of vertex or edge chunk.
+ *
+ */
 class ChunkPartitioner(partitions: Int, chunk_size: Long) extends Partitioner {
   require(partitions >= 0, s"Number of partitions ($partitions) cannot be negative.")
 
diff --git a/spark/src/main/scala/com/alibaba/graphar/writer/EdgeWriter.scala b/spark/src/main/scala/com/alibaba/graphar/writer/EdgeWriter.scala
index f3c49bb6a..b14f2f20c 100644
--- a/spark/src/main/scala/com/alibaba/graphar/writer/EdgeWriter.scala
+++ b/spark/src/main/scala/com/alibaba/graphar/writer/EdgeWriter.scala
@@ -29,6 +29,7 @@ import org.apache.spark.sql.functions._
 import scala.collection.SortedMap
 import scala.collection.mutable.ArrayBuffer
 
+/** Helper object for EdgeWriter class. */
 object EdgeWriter {
   // split the whole edge dataframe into chunk dataframes by vertex chunk size.
   private def split(edgeDf: DataFrame, keyColumnName: String, vertexChunkSize: Long): Seq[DataFrame] = {
@@ -102,6 +103,14 @@ object EdgeWriter {
   }
 }
 
+/** Writer for edge dataframe.
+ *
+ * @constructor create a new writer for edge dataframe with edge info.
+ * @param prefix the absolute prefix.
+ * @param edgeInfo the edge info that describes the ede type.
+ * @param adjListType the adj list type for the edge.
+ * @param edgeDf the input edge DataFrame.
+ */
 class EdgeWriter(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.Value, edgeDf: DataFrame) {
   private var chunks: Seq[DataFrame] = preprocess()
 
@@ -156,7 +165,7 @@ class EdgeWriter(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     }
   }
 
-  // generate the chunks of AdjList from edge dataframe for this edge type
+  /** Generate the chunks of AdjList from edge dataframe for this edge type. */
   def writeAdjList(): Unit = {
     val file_type = edgeInfo.getAdjListFileType(adjListType)
     var chunk_index: Long = 0
@@ -172,7 +181,10 @@ class EdgeWriter(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     }
   }
 
-  // generate the chunks of the property group from edge dataframe
+  /** Generate the chunks of the property group from edge dataframe.
+   *
+   * @param propertyGroup property group
+   */
   def writeEdgeProperties(propertyGroup: PropertyGroup): Unit = {
     if (edgeInfo.containPropertyGroup(propertyGroup, adjListType) == false) {
       throw new IllegalArgumentException
@@ -193,7 +205,7 @@ class EdgeWriter(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     }
   }
 
-  // generate the chunks of all property groups from edge dataframe
+  /** Generate the chunks of all property groups from edge dataframe. */
   def writeEdgeProperties(): Unit = {
     val property_groups = edgeInfo.getPropertyGroups(adjListType)
     val it = property_groups.iterator
@@ -203,7 +215,7 @@ class EdgeWriter(prefix: String,  edgeInfo: EdgeInfo, adjListType: AdjListType.V
     }
   }
 
-  // generate the chunks for the AdjList and all property groups from edge dataframe
+  /** Generate the chunks for the AdjList and all property groups from edge dataframe. */
   def writeEdges(): Unit = {
     writeAdjList()
     writeEdgeProperties()
diff --git a/spark/src/main/scala/com/alibaba/graphar/writer/VertexWriter.scala b/spark/src/main/scala/com/alibaba/graphar/writer/VertexWriter.scala
index 41780114c..4fb7b8670 100644
--- a/spark/src/main/scala/com/alibaba/graphar/writer/VertexWriter.scala
+++ b/spark/src/main/scala/com/alibaba/graphar/writer/VertexWriter.scala
@@ -31,6 +31,7 @@ import scala.collection.SortedMap
 import scala.collection.mutable.ArrayBuffer
 
 
+/** Helper object for VertexWriter class. */
 object VertexWriter {
   private def repartitionAndSort(vertexDf: DataFrame, chunkSize: Long): DataFrame = {
     val vertex_df_schema = vertexDf.schema
@@ -45,6 +46,13 @@ object VertexWriter {
   }
 }
 
+/** Writer for vertex DataFrame.
+ *
+ * @constructor create a new writer for vertex DataFrame with vertex info.
+ * @param prefix the absolute prefix.
+ * @param vertexInfo the vertex info that describes the vertex type.
+ * @param vertexDf the input vertex DataFrame.
+ */
 class VertexWriter(prefix: String, vertexInfo: VertexInfo, vertexDf: DataFrame) {
   private var chunks:DataFrame = preprocess()
   private val spark = vertexDf.sparkSession
@@ -58,7 +66,10 @@ class VertexWriter(prefix: String, vertexInfo: VertexInfo, vertexDf: DataFrame)
     return VertexWriter.repartitionAndSort(vertexDf, vertexInfo.getChunk_size())
   }
 
-  // generate chunks of the property group for vertex dataframe
+  /** Generate chunks of the property group for vertex dataframe.
+   *
+   * @param propertyGroup property group
+   */
   def writeVertexProperties(propertyGroup: PropertyGroup): Unit = {
     // check if contains the property group
     if (vertexInfo.containPropertyGroup(propertyGroup) == false) {
@@ -77,7 +88,7 @@ class VertexWriter(prefix: String, vertexInfo: VertexInfo, vertexDf: DataFrame)
     FileSystem.writeDataFrame(pg_df, propertyGroup.getFile_type(), output_prefix)
   }
 
-  // generate chunks of all property groups for vertex dataframe
+  /** Generate chunks of all property groups for vertex dataframe. */
   def writeVertexProperties(): Unit = {
     val property_groups = vertexInfo.getProperty_groups()
     val it = property_groups.iterator