[Java] enable int compression by default (#935)

* enable int compression by default

* Fix crash

* refine buffer varint tests

* fix test

docs/guide/java_object_graph_guide.md

@@ -138,8 +138,12 @@ ThreadSafeFury fury=Fury.builder()
 
 ### Smaller size
 `FuryBuilder#withIntCompressed`/`FuryBuilder#withLongCompressed` can be used to compress int/long for smaller size.
-Normally compress int is enough. If a number use long, it can't be represented by smaller bytes mostly. In such cases,
-compressing
+Normally compress int is enough. If a number are `long` type, it can't be represented by smaller bytes mostly, 
+the compression won't get good enough result, not worthy compared to performance cost.
+
+Both compression are enabled by default, if the serialized is not important, for example, you use flatbuffers for 
+serialization before, which doesn't compress anything, then you should disable compression. If your data are all numbers,
+the compression can bring 80% performance regression.
 
 ### Implement a customized serializer
 In some cases, you may want to implement a serializer for your type, especially some class customize serialization by JDK

java/fury-core/src/main/java/io/fury/Fury.java

@@ -1300,7 +1300,7 @@ public static final class FuryBuilder {
     boolean stringRefIgnored = true;
     boolean timeRefIgnored = true;
     ClassLoader classLoader;
-    boolean compressInt = false;
+    boolean compressInt = true;
     boolean compressLong = false;
     boolean compressString = true;
     CompatibleMode compatibleMode = CompatibleMode.SCHEMA_CONSISTENT;

java/fury-core/src/test/java/io/fury/serializer/CodegenSerializerTest.java

@@ -213,6 +213,7 @@ public void testCompressInt() {
       Fury fury1 =
           Fury.builder()
               .withLanguage(Language.JAVA)
+              .withIntCompressed(false)
               .withLongCompressed(true)
               .withCompatibleMode(CompatibleMode.SCHEMA_CONSISTENT)
               .requireClassRegistration(false)