com.google.protobuf.Descriptors.FileDescriptor#findExtensionByName ( )源码实例Demo

/**
 * Used in proto1 generated code only.
 *
 * After enabling bridge, we can define proto2 extensions (the extended type
 * is a proto2 mutable message) in a proto1 .proto file. For these extensions
 * we should generate proto2 GeneratedExtensions.
 */
public static <ContainingType extends Message, Type>
   GeneratedExtension<ContainingType, Type>
   newFileScopedGeneratedExtension(
       final Class singularType, final Message defaultInstance,
       final String descriptorOuterClass, final String extensionName) {
  // For extensions scoped within a file, we load the descriptor outer
  // class and rely on it to get the FileDescriptor which then can be
  // used to obtain the extension's FieldDescriptor.
  return new GeneratedExtension<ContainingType, Type>(
      new CachedDescriptorRetriever() {
        @Override
        protected FieldDescriptor loadDescriptor() {
          try {
            Class clazz = singularType.getClassLoader().loadClass(descriptorOuterClass);
            FileDescriptor file = (FileDescriptor) clazz.getField("descriptor").get(null);
            return file.findExtensionByName(extensionName);
          } catch (Exception e) {
            throw new RuntimeException(
                "Cannot load descriptors: "
                    + descriptorOuterClass
                    + " is not a valid descriptor class name",
                e);
          }
        }
      },
      singularType,
      defaultInstance,
      Extension.ExtensionType.MUTABLE);
}
 

/**
 * Used in proto1 generated code only.
 *
 * After enabling bridge, we can define proto2 extensions (the extended type
 * is a proto2 mutable message) in a proto1 .proto file. For these extensions
 * we should generate proto2 GeneratedExtensions.
 */
public static <ContainingType extends Message, Type>
   GeneratedExtension<ContainingType, Type>
   newFileScopedGeneratedExtension(
       final Class singularType, final Message defaultInstance,
       final String descriptorOuterClass, final String extensionName) {
  // For extensions scoped within a file, we load the descriptor outer
  // class and rely on it to get the FileDescriptor which then can be
  // used to obtain the extension's FieldDescriptor.
  return new GeneratedExtension<ContainingType, Type>(
      new CachedDescriptorRetriever() {
        protected FieldDescriptor loadDescriptor() {
          try {
            Class clazz =
                singularType.getClassLoader().loadClass(descriptorOuterClass);
            FileDescriptor file =
                (FileDescriptor) clazz.getField("descriptor").get(null);
            return file.findExtensionByName(extensionName);
          } catch (Exception e) {
            throw new RuntimeException(
                "Cannot load descriptors: " + descriptorOuterClass +
                " is not a valid descriptor class name", e);
          }
        }
      },
      singularType,
      defaultInstance,
      Extension.ExtensionType.MUTABLE);
}