feat: add withObjectMapper method to customize serialization of schemas to file

jsonschema-generator/src/main/java/com/github/victools/jsonschema/generator/SchemaGenerator.java

@@ -75,4 +75,13 @@ public ObjectNode generateSchema(Type mainTargetType, Type... typeParameters) {
     public SchemaBuilder buildMultipleSchemaDefinitions() {
         return SchemaBuilder.forMultipleTypes(this.config, this.typeContext);
     }
+
+    /**
+     * Returns the {@link SchemaGeneratorConfig} associated with this {@link SchemaGenerator}.
+     *
+     * @return a {@link SchemaGeneratorConfig} instance
+     */
+    public SchemaGeneratorConfig getConfig() {
+        return this.config;
+    }
 }

jsonschema-generator/src/main/java/com/github/victools/jsonschema/generator/SchemaGeneratorConfigBuilder.java

@@ -19,6 +19,7 @@
 import com.fasterxml.classmate.AnnotationInclusion;
 import com.fasterxml.jackson.core.json.JsonWriteFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
 import com.fasterxml.jackson.databind.node.JsonNodeFactory;
 import com.github.victools.jsonschema.generator.impl.SchemaGeneratorConfigImpl;
 import java.lang.annotation.Annotation;
@@ -41,7 +42,9 @@ public class SchemaGeneratorConfigBuilder {
      * @return default ObjectMapper instance
      */
     private static ObjectMapper createDefaultObjectMapper() {
-        ObjectMapper mapper = new ObjectMapper();
+        ObjectMapper mapper = new ObjectMapper()
+                // since version 4.32.0; pretty print by default (can be overridden by supplying explicit mapper)
+                .enable(SerializationFeature.INDENT_OUTPUT);
         mapper.getSerializationConfig()
                 // since version 4.21.0
                 .with(JsonWriteFeature.WRITE_NUMBERS_AS_STRINGS);
@@ -51,7 +54,7 @@ private static ObjectMapper createDefaultObjectMapper() {
         return mapper;
     }
 
-    private final ObjectMapper objectMapper;
+    private ObjectMapper objectMapper;
     private final OptionPreset preset;
     private final SchemaVersion schemaVersion;
 
@@ -306,4 +309,19 @@ public SchemaGeneratorConfigBuilder withAnnotationInclusionOverride(Class<? exte
         this.annotationInclusionOverrides.put(annotationType, override);
         return this;
     }
+
+    /**
+     * Register a custom {@link ObjectMapper} to create object and array nodes for the JSON structure being
+     * generated. Additionally, it is used to serialize a given schema, e.g., within the standard Maven plugin as
+     * either YAML or JSON.
+     *
+     * @param objectMapper supplier for object and array nodes for the JSON structure being generated
+     * @return this builder instance (for chaining)
+     *
+     * @since 4.32.0
+     */
+    public SchemaGeneratorConfigBuilder withObjectMapper(ObjectMapper objectMapper) {
+        this.objectMapper = objectMapper;
+        return this;
+    }
 }

jsonschema-generator/src/test/java/com/github/victools/jsonschema/generator/SchemaGeneratorConfigBuilderTest.java

@@ -16,6 +16,7 @@
 
 package com.github.victools.jsonschema.generator;
 
+import com.fasterxml.jackson.databind.ObjectMapper;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -49,6 +50,15 @@ public void testGetSetting_WithoutOption() {
         Assertions.assertFalse(this.builder.getSetting(Option.DEFINITIONS_FOR_ALL_OBJECTS));
     }
 
+    @Test
+    public void testWithObjectMapper() {
+        ObjectMapper currMapper = this.builder.getObjectMapper();
+        ObjectMapper newMapper = new ObjectMapper();
+        this.builder.withObjectMapper(newMapper);
+        Assertions.assertSame(newMapper, this.builder.getObjectMapper());
+        Assertions.assertNotEquals(currMapper, this.builder.getObjectMapper());
+    }
+
     @Test
     public void testForFields() {
         Assertions.assertNotNull(this.builder.forFields());

jsonschema-maven-plugin/src/main/java/com/github/victools/jsonschema/plugin/maven/SchemaGeneratorMojo.java

@@ -17,6 +17,7 @@
 package com.github.victools.jsonschema.plugin.maven;
 
 import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
 import com.github.victools.jsonschema.generator.Module;
 import com.github.victools.jsonschema.generator.Option;
 import com.github.victools.jsonschema.generator.OptionPreset;
@@ -626,9 +627,10 @@ private void addJacksonModule(SchemaGeneratorConfigBuilder configBuilder, Genera
      * @throws MojoExecutionException In case of problems when writing the targeted file
      */
     private void writeToFile(JsonNode jsonSchema, File file) throws MojoExecutionException {
+        ObjectMapper mapper = getGenerator().getConfig().getObjectMapper();
         try (FileOutputStream outputStream = new FileOutputStream(file);
                 PrintWriter writer = new PrintWriter(new OutputStreamWriter(outputStream, StandardCharsets.UTF_8))) {
-            writer.print(jsonSchema.toPrettyString());
+            writer.print(mapper.writeValueAsString(jsonSchema));
         } catch (IOException e) {
             throw new MojoExecutionException("Error: Can not write to file " + file, e);
         }

jsonschema-maven-plugin/src/test/java/com/github/victools/jsonschema/plugin/maven/SchemaGeneratorMojoTest.java

@@ -75,7 +75,12 @@ public void testGeneration(String testCaseName) throws Exception {
         File referenceFile = new File(testCaseLocation, testCaseName + "-reference.json");
         Assertions.assertTrue(referenceFile.exists());
         Assertions.assertTrue(FileUtils.contentEqualsIgnoreEOL(resultFile, referenceFile, CHARSET_NAME),
-                "Generated schema for " + testCaseName + " is not equal to the expected reference.");
+                "Generated schema for " + testCaseName + " is not equal to the expected reference.\n"
+                        + "Generated:\n"
+                        + FileUtils.readFileToString(resultFile)
+                        + "\n----------\n"
+                        + "Expected:\n"
+                        + FileUtils.readFileToString(referenceFile));
     }
 
     /**