diff --git a/java/libphonenumber/test/com/google/i18n/phonenumbers/RegionCode.java b/java/libphonenumber/test/com/google/i18n/phonenumbers/RegionCode.java
index 100cb29305..acd55ba0d0 100644
--- a/java/libphonenumber/test/com/google/i18n/phonenumbers/RegionCode.java
+++ b/java/libphonenumber/test/com/google/i18n/phonenumbers/RegionCode.java
@@ -20,8 +20,10 @@
 
 package com.google.i18n.phonenumbers;
 
+/**
+ * Class containing string constants of region codes for easier testing.
+ */
 final class RegionCode {
-  // Class containing string constants of region codes for easier testing.
   // Region code for global networks (e.g. +800 numbers).
   static final String UN001 = "001";
   static final String AD = "AD";
diff --git a/tools/java/java-build/pom.xml b/tools/java/java-build/pom.xml
index 120043dc1f..2548ac58c1 100644
--- a/tools/java/java-build/pom.xml
+++ b/tools/java/java-build/pom.xml
@@ -115,6 +115,31 @@
       <version>4.13.2</version>
       <scope>test</scope>
     </dependency>
+    <!-- https://mvnrepository.com/artifact/com.google.auto.value/auto-value -->
+    <dependency>
+        <groupId>com.google.auto.value</groupId>
+        <artifactId>auto-value</artifactId>
+        <version>1.11.0</version>
+        <scope>provided</scope>
+    </dependency>
+    <!-- https://mvnrepository.com/artifact/com.google.auto.value/auto-value-annotations -->
+    <dependency>
+        <groupId>com.google.auto.value</groupId>
+        <artifactId>auto-value-annotations</artifactId>
+        <version>1.11.0</version>
+    </dependency>
+    <!-- https://mvnrepository.com/artifact/com.google.code.findbugs/jsr305 -->
+    <dependency>
+        <groupId>com.google.code.findbugs</groupId>
+        <artifactId>jsr305</artifactId>
+        <version>3.0.2</version>
+    </dependency>
+    <!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
+    <dependency>
+        <groupId>com.google.guava</groupId>
+        <artifactId>guava</artifactId>
+        <version>33.3.0-jre</version>
+    </dependency>
   </dependencies>
 
 </project>
diff --git a/tools/java/java-build/src/com/google/i18n/phonenumbers/BuildMetadataProtoFromXml.java b/tools/java/java-build/src/com/google/i18n/phonenumbers/BuildMetadataProtoFromXml.java
index 748d263510..c4fdf92f41 100644
--- a/tools/java/java-build/src/com/google/i18n/phonenumbers/BuildMetadataProtoFromXml.java
+++ b/tools/java/java-build/src/com/google/i18n/phonenumbers/BuildMetadataProtoFromXml.java
@@ -16,6 +16,8 @@
 
 package com.google.i18n.phonenumbers;
 
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableSortedSet;
 import com.google.i18n.phonenumbers.Phonemetadata.PhoneMetadata;
 import com.google.i18n.phonenumbers.Phonemetadata.PhoneMetadataCollection;
 
@@ -35,6 +37,7 @@
 import java.util.TreeSet;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
+import javax.annotation.Nullable;
 
 /**
  * Tool to convert phone number metadata from the XML format to protocol buffer format.
@@ -101,9 +104,25 @@ public class BuildMetadataProtoFromXml extends Command {
       "/* This file is automatically generated by {@link " + CLASS_NAME + "}.\n" +
       " * Please don't modify it directly.\n" +
       " */\n\n";
+  
+  private static final String MAP_COMMENT =
+      "  // A mapping from a country code to the region codes which denote the\n" +
+      "  // country/region represented by that country code. In the case of multiple\n" +
+      "  // countries sharing a calling code, such as the NANPA countries, the one\n" +
+      "  // indicated with \"isMainCountryForCode\" in the metadata should be first.\n";
+  private static final String COUNTRY_CODE_SET_COMMENT =
+      "  // A set of all country codes for which data is available.\n";
+  private static final String REGION_CODE_SET_COMMENT =
+      "  // A set of all region codes for which data is available.\n";
+  private static final double CAPACITY_FACTOR = 0.75;
+  private static final String CAPACITY_COMMENT =
+      "    // The capacity is set to %d as there are %d different entries,\n" +
+      "    // and this offers a load factor of roughly " + CAPACITY_FACTOR + ".\n";
 
-  private static final String REGION_CODE_CONSTS_COMMENT =
-      "  // Class containing string constants of region codes for easier testing.\n";
+  private static final String REGION_CODE_CONSTS_JAVADOC =
+      "/**\n" +
+      " * Class containing string constants of region codes for easier testing.\n" +
+      " */\n";
 
   @Override
   public String getCommandName() {
@@ -241,20 +260,6 @@ private void deleteAllFilesForPrefix(String filePrefix) {
     System.out.println("Deleted " + counter + " old files");
   }
 
-  private static final String MAP_COMMENT =
-      "  // A mapping from a country code to the region codes which denote the\n" +
-      "  // country/region represented by that country code. In the case of multiple\n" +
-      "  // countries sharing a calling code, such as the NANPA countries, the one\n" +
-      "  // indicated with \"isMainCountryForCode\" in the metadata should be first.\n";
-  private static final String COUNTRY_CODE_SET_COMMENT =
-      "  // A set of all country codes for which data is available.\n";
-  private static final String REGION_CODE_SET_COMMENT =
-      "  // A set of all region codes for which data is available.\n";
-  private static final double CAPACITY_FACTOR = 0.75;
-  private static final String CAPACITY_COMMENT =
-      "    // The capacity is set to %d as there are %d different entries,\n" +
-      "    // and this offers a load factor of roughly " + CAPACITY_FACTOR + ".\n";
-
   private static void writeCountryCallingCodeMappingToJavaFile(
       Map<Integer, List<String>> countryCodeToRegionCodeMap,
       String outputDir, String mappingClass, String copyright) throws IOException {
@@ -269,7 +274,11 @@ private static void writeCountryCallingCodeMappingToJavaFile(
     }
     boolean hasCountryCodes = countryCodeToRegionCodeMap.size() > 1;
 
-    ClassWriter writer = new ClassWriter(outputDir, mappingClass, copyright);
+    ClassWriter.Builder writer = ClassWriter.builder()
+        .setOutputDir(outputDir)
+        .setCopyright(Integer.parseInt(copyright))
+        .setModifiers("public")
+        .setName(mappingClass);
 
     int capacity = (int) (countryCodeToRegionCodeMap.size() / CAPACITY_FACTOR);
     if (hasRegionCodes && hasCountryCodes) {
@@ -282,10 +291,10 @@ private static void writeCountryCallingCodeMappingToJavaFile(
       writeRegionCodeSet(writer, capacity, regionCodeList);
     }
 
-    writer.writeToFile();
+    writer.build().writeToFile();
   }
 
-  private static void writeMap(ClassWriter writer, int capacity,
+  private static void writeMap(ClassWriter.Builder writer, int capacity,
                                Map<Integer, List<String>> countryCodeToRegionCodeMap) {
     writer.addToBody(MAP_COMMENT);
 
@@ -319,7 +328,7 @@ private static void writeMap(ClassWriter writer, int capacity,
     writer.addToBody("  }\n");
   }
 
-  private static void writeRegionCodeSet(ClassWriter writer, int capacity,
+  private static void writeRegionCodeSet(ClassWriter.Builder writer, int capacity,
                                          List<String> regionCodeList) {
     writer.addToBody(REGION_CODE_SET_COMMENT);
 
@@ -340,7 +349,7 @@ private static void writeRegionCodeSet(ClassWriter writer, int capacity,
     writer.addToBody("  }\n");
   }
 
-  private static void writeCountryCodeSet(ClassWriter writer, int capacity,
+  private static void writeCountryCodeSet(ClassWriter.Builder writer, int capacity,
                                           Set<Integer> countryCodeSet) {
     writer.addToBody(COUNTRY_CODE_SET_COMMENT);
 
@@ -361,9 +370,15 @@ private static void writeCountryCodeSet(ClassWriter writer, int capacity,
     writer.addToBody("  }\n");
   }
 
-  private static void writeRegionCodeConstantsToJavaFile(Collection<String> regionCodeList, String outputDir, String copyright) throws IOException {
-    ClassWriter writer = new ClassWriter(outputDir, "RegionCode", copyright, "final");
-    writer.addToBody(REGION_CODE_CONSTS_COMMENT);
+  private static void writeRegionCodeConstantsToJavaFile(Collection<String> regionCodeList,
+                                                         String outputDir, String copyright) throws IOException {
+    ClassWriter.Builder writer = ClassWriter.builder()
+        .setOutputDir(outputDir)
+        .setName("RegionCode")
+        .setModifiers("final")
+        .setCopyright(Integer.parseInt(copyright));
+
+    writer.addToJavadoc(REGION_CODE_CONSTS_JAVADOC);
     
     for (String regionCode : regionCodeList) {
       String variableName = regionCode.toUpperCase();
@@ -376,60 +391,89 @@ private static void writeRegionCodeConstantsToJavaFile(Collection<String> region
       writer.addToBody("  static final String " + variableName + " = \"" + regionCode + "\";\n");
     }
     
-    writer.writeToFile();
+    writer.build().writeToFile();
   }
 
-  private static final class ClassWriter {
-    private final String name;
-    private final String copyright;
-    private final String modifiers;
-
-    private final SortedSet<String> imports;
-    private final StringBuffer body;
-    private final Formatter formatter;
-    private final Writer writer;
-
-    ClassWriter(String outputDir, String name, String copyright, String modifiers) throws IOException {
-      this.name = name;
-      this.copyright = copyright;
-      this.modifiers = modifiers;
-
-      imports = new TreeSet<String>();
-      body = new StringBuffer();
-      formatter = new Formatter(body);
-      writer = new BufferedWriter(new FileWriter(new File(outputDir, name + ".java")));
-    }
 
-    ClassWriter(String outputDir, String name, String copyright) throws IOException {
-      this(outputDir, name, copyright, "public");
+  @AutoValue
+  abstract static class ClassWriter {
+    abstract String outputDir();
+    
+    abstract Integer copyright();
+    abstract ImmutableSortedSet<String> imports();
+    abstract String javadoc();
+    abstract String modifiers();
+    abstract String name();
+    abstract String body();
+
+    static Builder builder() {
+      return new AutoValue_BuildMetadataProtoFromXml_ClassWriter.Builder()
+          .setModifiers("");
     }
 
-    void addToImports(String name) {
-      imports.add(name);
-    }
+    @AutoValue.Builder
+    abstract static class Builder {
+      abstract Builder setOutputDir(String outputDir);
+      
+      abstract Builder setCopyright(Integer copyright);
+      
+      abstract ImmutableSortedSet.Builder<String> importsBuilder();
+      final Builder addToImports(String name) {
+        importsBuilder().add(name);
+        return this;
+      }
 
-    void addToBody(CharSequence text) {
-      body.append(text);
-    }
+      abstract Builder setJavadoc(String javadoc);
+      private final StringBuilder javadocBuilder = new StringBuilder();
+      final Builder addToJavadoc(String text) {
+        javadocBuilder.append(text);
+        return this;
+      }
+      
+      abstract Builder setName(String name);
+      abstract Builder setModifiers(String modifiers);
+      
+      abstract Builder setBody(String body);
+      private final StringBuilder bodyBuilder = new StringBuilder();
+      final Builder addToBody(String text) {
+        bodyBuilder.append(text);
+        return this;
+      }
+      final Builder formatToBody(String format, Object... args) {
+        Formatter formatter = new Formatter(bodyBuilder);
+        formatter.format(format, args);
+        return this;
+      }
 
-    void formatToBody(String format, Object... args) {
-      formatter.format(format, args);
+      abstract ClassWriter autoBuild();
+      
+      final ClassWriter build() {
+        setJavadoc(javadocBuilder.toString());
+        setBody(bodyBuilder.toString());
+        return autoBuild();
+      }
     }
 
     void writeToFile() throws IOException {
-      CopyrightNotice.writeTo(writer, Integer.valueOf(copyright));
+      Writer writer = new BufferedWriter(new FileWriter(new File(outputDir(), name() + ".java")));
+
+      CopyrightNotice.writeTo(writer, copyright());
       writer.write(GENERATION_COMMENT);
       writer.write("package " + PACKAGE_NAME + ";\n\n");
 
-      if (!imports.isEmpty()) {
-        for (String item : imports) {
+      if (!imports().isEmpty()) {
+        for (String item : imports()) {
           writer.write("import " + item + ";\n");
         }
         writer.write("\n");
       }
 
-      writer.write((modifiers.isEmpty() ? "" : modifiers + " ") + "class " + name + " {\n");
-      writer.write(body.toString());
+      writer.write(javadoc());
+      if (!modifiers().isEmpty()) {
+        writer.write(modifiers() + " ");
+      }
+      writer.write("class " + name() + " {\n");
+      writer.write(body());
       writer.write("}\n");
 
       writer.flush();