add dubbo attachment readme

Author: ipipman

README.md

@@ -17,4 +17,6 @@
 - ##### [分布式服务框架Dubbo（缓存策略）](https://github.com/ipipman/JavaSpringBootSamples/tree/master/dubbo-cache-sample "分布式服务框架Dubbo（缓存策略）")
 - ##### [分布式服务框架Dubbo（参数回调）](https://github.com/ipipman/JavaSpringBootSamples/tree/master/dubbo-callback-sample "分布式服务框架Dubbo（参数回调）")
 - ##### [分布式服务框架Dubbo（基于HTTP传输协议）](https://github.com/ipipman/JavaSpringBootSamples/tree/master/dubbo-http-sample "分布式服务框架Dubbo（基于HTTP传输协议）")
-- ##### [分布式服务框架Dubbo（本地调用）](https://github.com/ipipman/JavaSpringBootSamples/tree/master/dubbo-local-sample "分布式服务框架Dubbo（本地调用）")
+- ##### [分布式服务框架Dubbo（本地调用）](https://github.com/ipipman/JavaSpringBootSamples/tree/master/dubbo-local-sample "分布式服务框架Dubbo（本地调用）")
+- ##### [分布式服务框架Dubbo（隐式参数）](https://github.com/ipipman/JavaSpringBootSamples/tree/master/dubbo-attachment-sample "分布式服务框架Dubbo（隐式参数）")
+

dubbo-attachment-sample/README.md

@@ -0,0 +1,43 @@
+# 分布式服务框架之Dubbo（隐式参数）
+
+### 隐式参数
+通过 Dubbo 中的 Attachment 在服务消费方和提供方之间隐式传递参数。
+注意：path, group, version, dubbo, token, timeout 几个 key 是保留字段，请使用其它值。
+
+<img src="https://ipman-blog-1304583208.cos.ap-nanjing.myqcloud.com/dubbo/1031608635201_.pic_hd.jpg" width = "620" height = "160" alt="图片名称" align=center />
+
+### Dubbo隐式参数实战
+##### 1.客户端通过setAttachment设置隐式参数，在完成下面一次远程调用会被清空，即多次远程调用要多次设置
+```java
+public class AttachmentConsumer {
+
+    public static void main(String[] args) {
+        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring/attachment-consumer.xml");
+        AttachmentService attachmentService = context.getBean("attachmentService", AttachmentService.class);
+        // 隐式传参，后面的远程调用都会隐式将这些参数发送到服务器端，类似cookie
+        RpcContext.getContext().setAttachment("index", "1");
+
+        // 业务，远程调用
+        // Hello ipman, response from provider: 10.13.224.253:20880, attachment - index: 1
+        System.out.println(attachmentService.sayHello("ipman"));
+    }
+}
+```
+
+##### 2.服务端通过getAttachment获取隐式参数
+```java
+public class AttachmentServiceImpl implements AttachmentService {
+    @Override
+    public String sayHello(String name) {
+
+        RpcContext context = RpcContext.getContext();
+        //获取客户端隐式传入的参数
+        String index = (String) context.getAttachment("index");
+
+        System.out.println("[" + new SimpleDateFormat("HH:mm:ss").format(new Date()) + "] Hello " + name +
+                ", request from consumer: " + context.getRemoteAddress());
+        return "Hello " + name + ", response from provider: " + context.getLocalAddress() +
+                ", attachment - index: " + index;
+    }
+}
+```