diff --git a/conformance/ConformanceJava.java b/conformance/ConformanceJava.java
new file mode 100644
index 0000000..a983ba3
--- /dev/null
+++ b/conformance/ConformanceJava.java
@@ -0,0 +1,142 @@
+
+import com.google.protobuf.conformance.Conformance;
+import com.google.protobuf.util.JsonFormat;
+import com.google.protobuf.util.JsonFormat.TypeRegistry;
+import com.google.protobuf.InvalidProtocolBufferException;
+
+class ConformanceJava {
+  private int testCount = 0;
+  private TypeRegistry typeRegistry;
+
+  private boolean readFromStdin(byte[] buf, int len) throws Exception {
+    int ofs = 0;
+    while (len > 0) {
+      int read = System.in.read(buf, ofs, len);
+      if (read == -1) {
+        return false;  // EOF
+      }
+      ofs += read;
+      len -= read;
+    }
+
+    return true;
+  }
+
+  private void writeToStdout(byte[] buf) throws Exception {
+    System.out.write(buf);
+  }
+
+  // Returns -1 on EOF (the actual values will always be positive).
+  private int readLittleEndianIntFromStdin() throws Exception {
+    byte[] buf = new byte[4];
+    if (!readFromStdin(buf, 4)) {
+      return -1;
+    }
+    return (buf[0] & 0xff)
+        | ((buf[1] & 0xff) << 8)
+        | ((buf[2] & 0xff) << 16)
+        | ((buf[3] & 0xff) << 24);
+  }
+
+  private void writeLittleEndianIntToStdout(int val) throws Exception {
+    byte[] buf = new byte[4];
+    buf[0] = (byte)val;
+    buf[1] = (byte)(val >> 8);
+    buf[2] = (byte)(val >> 16);
+    buf[3] = (byte)(val >> 24);
+    writeToStdout(buf);
+  }
+
+  private Conformance.ConformanceResponse doTest(Conformance.ConformanceRequest request) {
+    Conformance.TestAllTypes testMessage;
+
+    switch (request.getPayloadCase()) {
+      case PROTOBUF_PAYLOAD: {
+        try {
+          testMessage = Conformance.TestAllTypes.parseFrom(request.getProtobufPayload());
+        } catch (InvalidProtocolBufferException e) {
+          return Conformance.ConformanceResponse.newBuilder().setParseError(e.getMessage()).build();
+        }
+        break;
+      }
+      case JSON_PAYLOAD: {
+        try {
+          Conformance.TestAllTypes.Builder builder = Conformance.TestAllTypes.newBuilder();
+          JsonFormat.parser().usingTypeRegistry(typeRegistry)
+              .merge(request.getJsonPayload(), builder);
+          testMessage = builder.build();
+        } catch (InvalidProtocolBufferException e) {
+          return Conformance.ConformanceResponse.newBuilder().setParseError(e.getMessage()).build();
+        }
+        break;
+      }
+      case PAYLOAD_NOT_SET: {
+        throw new RuntimeException("Request didn't have payload.");
+      }
+
+      default: {
+        throw new RuntimeException("Unexpected payload case.");
+      }
+    }
+
+    switch (request.getRequestedOutputFormat()) {
+      case UNSPECIFIED:
+        throw new RuntimeException("Unspecified output format.");
+
+      case PROTOBUF:
+        return Conformance.ConformanceResponse.newBuilder().setProtobufPayload(testMessage.toByteString()).build();
+
+      case JSON:
+        try {
+          return Conformance.ConformanceResponse.newBuilder().setJsonPayload(
+              JsonFormat.printer().usingTypeRegistry(typeRegistry).print(testMessage)).build();
+        } catch (InvalidProtocolBufferException | IllegalArgumentException e) {
+          return Conformance.ConformanceResponse.newBuilder().setSerializeError(
+              e.getMessage()).build();
+        }
+
+      default: {
+        throw new RuntimeException("Unexpected request output.");
+      }
+    }
+  }
+
+  private boolean doTestIo() throws Exception {
+    int bytes = readLittleEndianIntFromStdin();
+
+    if (bytes == -1) {
+      return false;  // EOF
+    }
+
+    byte[] serializedInput = new byte[bytes];
+
+    if (!readFromStdin(serializedInput, bytes)) {
+      throw new RuntimeException("Unexpected EOF from test program.");
+    }
+
+    Conformance.ConformanceRequest request =
+        Conformance.ConformanceRequest.parseFrom(serializedInput);
+    Conformance.ConformanceResponse response = doTest(request);
+    byte[] serializedOutput = response.toByteArray();
+
+    writeLittleEndianIntToStdout(serializedOutput.length);
+    writeToStdout(serializedOutput);
+
+    return true;
+  }
+
+  public void run() throws Exception {
+    typeRegistry = TypeRegistry.newBuilder().add(
+        Conformance.TestAllTypes.getDescriptor()).build();
+    while (doTestIo()) {
+      // Empty.
+    }
+
+    System.err.println("ConformanceJava: received EOF from test runner after " +
+        this.testCount + " tests");
+  }
+
+  public static void main(String[] args) throws Exception {
+    new ConformanceJava().run();
+  }
+}