Descriptors.java 文件源码

/**
 * Construct a {@code FileDescriptor}.
 *
 * @param proto The protocol message form of the FileDescriptor.
 * @param dependencies {@code FileDescriptor}s corresponding to all of
 *                     the file's dependencies.
 * @param allowUnknownDependencies If true, non-exist dependenncies will be
 *           ignored and undefined message types will be replaced with a
 *           placeholder type.
 * @throws DescriptorValidationException {@code proto} is not a valid
 *           descriptor.  This can occur for a number of reasons, e.g.
 *           because a field has an undefined type or because two messages
 *           were defined with the same name.
 */
public static FileDescriptor buildFrom(
    final FileDescriptorProto proto, final FileDescriptor[] dependencies,
    final boolean allowUnknownDependencies)
    throws DescriptorValidationException {
  // Building descriptors involves two steps:  translating and linking.
  // In the translation step (implemented by FileDescriptor's
  // constructor), we build an object tree mirroring the
  // FileDescriptorProto's tree and put all of the descriptors into the
  // DescriptorPool's lookup tables.  In the linking step, we look up all
  // type references in the DescriptorPool, so that, for example, a
  // FieldDescriptor for an embedded message contains a pointer directly
  // to the Descriptor for that message's type.  We also detect undefined
  // types in the linking step.
  final DescriptorPool pool = new DescriptorPool(
      dependencies, allowUnknownDependencies);
  final FileDescriptor result = new FileDescriptor(
      proto, dependencies, pool, allowUnknownDependencies);
  result.crossLink();
  return result;
}