add java doc

java/README.md

-## Java Demo
+## Tutorial of Java Client for Paddle Serving
+
+(English|[简体中文](./README_CN.md))
+
+### Development Environment
+
+In order to facilitate users to use java for development, we provide the compiled Serving project to be placed in the java mirror. The way to get the mirror and enter the development environment is
+
+```
+docker pull hub.baidubce.com/paddlepaddle/serving:0.4.0-java
+docker run --rm -dit --name java_serving hub.baidubce.com/paddlepaddle/serving:0.4.0-java
+docker exec -it java_serving bash
+cd Serving/java
+```
+
+The Serving folder is at the develop branch when the docker image is generated. You need to git pull to the latest version or git checkout to the desired branch.
+
+### Install client dependencies
+
+Due to the large number of dependent libraries, the image has been compiled once at the time of generation, and the user can perform the following operations
 
-### Install package
 ```
 mvn compile
 mvn install
@@ -9,18 +27,49 @@ mvn compile
 mvn install
 ```
 
-### Start Server
+### Start the server
 
-take the fit_a_line demo as example
+Take the fit_a_line model as an example, the server starts
 
 ```
- python -m paddle_serving_server.serve --model uci_housing_model --thread 10 --port 9393 --use_multilang #CPU
-python -m paddle_serving_server_gpu.serve --model uci_housing_model --thread 10 --port 9393 --use_multilang #GPU
+cd ../../python/examples/fit_a_line
+sh get_data.sh
+python -m paddle_serving_server.serve --model uci_housing_model --thread 10 --port 9393 --use_multilang &
 ```
 
-### Client Predict
+Client prediction
+
 ```
+cd ../../../java/examples/target
 java -cp paddle-serving-sdk-java-examples-0.0.1-jar-with-dependencies.jar PaddleServingClientExample fit_a_line
 ```
 
-The Java example also contains the prediction client of Bert, Model_enaemble, asyn_predict, batch_predict, Cube_local, Cube_quant, and Yolov4 models.
+Take yolov4 as an example, the server starts
+
+```
+python -m paddle_serving_app.package --get_model yolov4
+tar -xzvf yolov4.tar.gz
+python -m paddle_serving_server_gpu.serve --model yolov4_model --port 9393 --gpu_ids 0 --use_multilang & #It needs to be executed in GPU Docker, otherwise the execution method of CPU must be used.
+```
+
+Client prediction
+
+```
+# in /Serving/java/examples/target
+java -cp paddle-serving-sdk-java-examples-0.0.1-jar-with-dependencies.jar PaddleServingClientExample yolov4 ../../../python/examples/yolov4/000000570688.jpg
+# The case of yolov4 needs to specify a picture as input
+```
+
+### Customization guidance
+
+The above example is running in CPU mode. If GPU mode is required, there are two options.
+
+The first is that GPU Serving and Java Client are in the same image. After starting the corresponding image, the user needs to move /Serving/java in the java image to the corresponding image.
+
+The second is to deploy GPU Serving and Java Client separately. If they are on the same host, you can learn the IP address of the corresponding container through ifconfig, and then when you connect to client.connect in `examples/src/main/java/PaddleServingClientExample.java` Make changes to the endpoint, and then compile it again. Or select `--net=host` to bind the network device of docker and host when docker starts, so that it can run directly without customizing java code.
+
+**It should be noted that in the example, all models need to use `--use_multilang` to start GRPC multi-programming language support, and the port number is 9393. If you need another port, you need to modify it in the java file**
+
+**Currently Serving has launched the Pipeline mode (see [Pipeline Serving](../doc/PIPELINE_SERVING.md) for details). The next version (0.4.1) of the Pipeline Serving Client for Java will be released. **
+
+

java/README_CN.md

-## Java 示例
+## 用于Paddle Serving的Java客户端
+
+([English](./README.md)|简体中文)
+
+### 开发环境
+
+为了方便用户使用java进行开发，我们提供了编译好的Serving工程放置在java镜像当中，获取镜像并进入开发环境的方式是
+
+```
+docker pull hub.baidubce.com/paddlepaddle/serving:0.4.0-java
+docker run --rm -dit --name java_serving hub.baidubce.com/paddlepaddle/serving:0.4.0-java
+docker exec -it java_serving bash
+cd Serving/java
+```
+
+Serving文件夹是镜像生成时的develop分支工程目录，需要git pull 到最新版本，或者git checkout 到想要的分支。
 
 ### 安装客户端依赖
+
+由于依赖库数量庞大，因此镜像已经在生成时编译过一次，用户执行以下操作即可
+
 ```
 mvn compile
 mvn install
@@ -11,16 +29,47 @@ mvn install
 
 ### 启动服务端
 
-以fit_a_line模型为例
+以fit_a_line模型为例，服务端启动
 
 ```
- python -m paddle_serving_server.serve --model uci_housing_model --thread 10 --port 9393 --use_multilang #CPU
-python -m paddle_serving_server_gpu.serve --model uci_housing_model --thread 10 --port 9393 --use_multilang #GPU
+cd ../../python/examples/fit_a_line
+sh get_data.sh
+python -m paddle_serving_server.serve --model uci_housing_model --thread 10 --port 9393 --use_multilang &
 ```
 
-### 客户端预测
+客户端预测
+
 ```
+cd ../../../java/examples/target
 java -cp paddle-serving-sdk-java-examples-0.0.1-jar-with-dependencies.jar PaddleServingClientExample fit_a_line
 ```
 
-java示例中还包含了bert、model_enaemble、asyn_predict、batch_predict、cube_local、cube_quant、yolov4模型的预测客户端。
+以yolov4为例子，服务端启动
+
+```
+python -m paddle_serving_app.package --get_model yolov4
+tar -xzvf yolov4.tar.gz
+python -m paddle_serving_server_gpu.serve --model yolov4_model --port 9393 --gpu_ids 0 --use_multilang &  #需要在GPU Docker当中执行，否则要使用CPU的执行方式。
+```
+
+客户端预测
+
+```
+# in /Serving/java/examples/target
+java -cp paddle-serving-sdk-java-examples-0.0.1-jar-with-dependencies.jar PaddleServingClientExample yolov4 ../../../python/examples/yolov4/000000570688.jpg
+# yolov4的案例需要指定一个图片作为输入
+```
+
+### 二次开发指导
+
+上述示例是在CPU模式下运行，如果需要GPU模式，可以有两种选择。
+
+第一种是GPU Serving和Java Client在同一个镜像，需要用户在启动对应的镜像后，把java镜像当中的/Serving/java移动到对应的镜像中。
+
+第二种是GPU Serving和Java Client分开部署，如果在同一台宿主机，可以通过ifconfig了解对应容器的IP地址，然后在`examples/src/main/java/PaddleServingClientExample.java`当中对client.connect时的endpoint做修改，然后再编译一次。 或者在docker启动时选择 `--net=host`来绑定docker和宿主机的网络设备，这样不需要定制java代码可以直接运行。
+
+**需要注意的是，在示例中，所有模型都需要使用`--use_multilang`来启动GRPC多编程语言支持，以及端口号都是9393，如果需要别的端口，需要在java文件里修改**
+
+**目前Serving已推出Pipeline模式（详见[Pipeline Serving](../doc/PIPELINE_SERVING_CN.md)），下个版本（0.4.1）面向Java的Pipeline Serving Client将会发布，敬请期待。**
+
+