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add dubbo notify sample
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‎dubbo-notify-sample/.gitignore

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HELP.md
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target/
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!.mvn/wrapper/maven-wrapper.jar
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!**/src/main/**/target/
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!**/src/test/**/target/
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### STS ###
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.apt_generated
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.classpath
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.factorypath
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.project
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.settings
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.springBeans
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.sts4-cache
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### IntelliJ IDEA ###
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.idea
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*.iws
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*.iml
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*.ipr
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### NetBeans ###
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/nbproject/private/
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/nbbuild/
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/dist/
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/nbdist/
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/.nb-gradle/
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build/
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!**/src/main/**/build/
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!**/src/test/**/build/
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### VS Code ###
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.vscode/

‎dubbo-notify-sample/.mvn/wrapper/MavenWrapperDownloader.java

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/*
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* Copyright 2007-present the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* https://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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import java.net.*;
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import java.io.*;
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import java.nio.channels.*;
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import java.util.Properties;
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public class MavenWrapperDownloader {
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private static final String WRAPPER_VERSION = "0.5.6";
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/**
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* Default URL to download the maven-wrapper.jar from, if no 'downloadUrl' is provided.
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*/
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private static final String DEFAULT_DOWNLOAD_URL = "https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/"
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+ WRAPPER_VERSION + "/maven-wrapper-" + WRAPPER_VERSION + ".jar";
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/**
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* Path to the maven-wrapper.properties file, which might contain a downloadUrl property to
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* use instead of the default one.
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*/
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private static final String MAVEN_WRAPPER_PROPERTIES_PATH =
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".mvn/wrapper/maven-wrapper.properties";
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/**
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* Path where the maven-wrapper.jar will be saved to.
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*/
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private static final String MAVEN_WRAPPER_JAR_PATH =
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".mvn/wrapper/maven-wrapper.jar";
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/**
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* Name of the property which should be used to override the default download url for the wrapper.
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*/
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private static final String PROPERTY_NAME_WRAPPER_URL = "wrapperUrl";
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public static void main(String args[]) {
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System.out.println("- Downloader started");
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File baseDirectory = new File(args[0]);
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System.out.println("- Using base directory: " + baseDirectory.getAbsolutePath());
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// If the maven-wrapper.properties exists, read it and check if it contains a custom
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// wrapperUrl parameter.
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File mavenWrapperPropertyFile = new File(baseDirectory, MAVEN_WRAPPER_PROPERTIES_PATH);
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String url = DEFAULT_DOWNLOAD_URL;
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if(mavenWrapperPropertyFile.exists()) {
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FileInputStream mavenWrapperPropertyFileInputStream = null;
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try {
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mavenWrapperPropertyFileInputStream = new FileInputStream(mavenWrapperPropertyFile);
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Properties mavenWrapperProperties = new Properties();
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mavenWrapperProperties.load(mavenWrapperPropertyFileInputStream);
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url = mavenWrapperProperties.getProperty(PROPERTY_NAME_WRAPPER_URL, url);
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} catch (IOException e) {
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System.out.println("- ERROR loading '" + MAVEN_WRAPPER_PROPERTIES_PATH + "'");
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} finally {
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try {
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if(mavenWrapperPropertyFileInputStream != null) {
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mavenWrapperPropertyFileInputStream.close();
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}
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} catch (IOException e) {
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// Ignore ...
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}
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}
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}
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System.out.println("- Downloading from: " + url);
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File outputFile = new File(baseDirectory.getAbsolutePath(), MAVEN_WRAPPER_JAR_PATH);
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if(!outputFile.getParentFile().exists()) {
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if(!outputFile.getParentFile().mkdirs()) {
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System.out.println(
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"- ERROR creating output directory '" + outputFile.getParentFile().getAbsolutePath() + "'");
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}
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}
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System.out.println("- Downloading to: " + outputFile.getAbsolutePath());
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try {
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downloadFileFromURL(url, outputFile);
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System.out.println("Done");
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System.exit(0);
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} catch (Throwable e) {
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System.out.println("- Error downloading");
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e.printStackTrace();
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System.exit(1);
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}
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}
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private static void downloadFileFromURL(String urlString, File destination) throws Exception {
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if (System.getenv("MVNW_USERNAME") != null && System.getenv("MVNW_PASSWORD") != null) {
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String username = System.getenv("MVNW_USERNAME");
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char[] password = System.getenv("MVNW_PASSWORD").toCharArray();
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Authenticator.setDefault(new Authenticator() {
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@Override
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protected PasswordAuthentication getPasswordAuthentication() {
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return new PasswordAuthentication(username, password);
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}
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});
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}
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URL website = new URL(urlString);
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ReadableByteChannel rbc;
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rbc = Channels.newChannel(website.openStream());
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FileOutputStream fos = new FileOutputStream(destination);
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fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
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fos.close();
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rbc.close();
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}
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}

‎dubbo-notify-sample/.mvn/wrapper/maven-wrapper.jar

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‎dubbo-notify-sample/.mvn/wrapper/maven-wrapper.properties

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distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.6.3/apache-maven-3.6.3-bin.zip
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wrapperUrl=https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/0.5.6/maven-wrapper-0.5.6.jar

‎dubbo-notify-sample/README.md

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# 分布式服务框架之Dubbo（事件通知）
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### Dubbo实现的几种调用方式
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Dubbo协议采用单一长连接，底层实现是Netty的NIO异步通讯机制；基于这种机制，Dubbo实现了以下几种调用方式：
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> - 同步调用；
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> - 异步调用；
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> - 参数回调；
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> - 事件通知；
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### 同步调用
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同步调用是一种阻塞的调用方式，即Consumer端代码一直阻塞等待，直到Provider端返回为止；
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通常，一个典型的同步调用过程如下：
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1. Consumer业务线程调用远程接口，向Provider发送请求，同时当前线程处于阻塞状态；
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2. Provider接到Consumer的请求后，开始处理请求，将结果返回给Consumer；
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3. Consumer收到结果后，当前线程继续往后执行；
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这里有2个问题：
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1. Consumer业务线程是怎么进入阻塞状态的？
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2. Consumer收到结果后，如何唤醒业务线程往后执行的？
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其实，Dubbo的底层IO操作都是异步的。Consumer端发起调用后，得到一个Future对象。对于同步调用，业务线程通过Future.get(timeout)，阻塞等待Provider端将结果返回。timeout则是Consumer定义的超时时间。当结果返回后，会设置到此Future，并且唤醒阻塞的业务线程，当超时时间到结果还未返回时，业务线将会异步返回。
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### 异步调用
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给予Dubbo底层的异步NIO实现异步调用，对于Provider响应时间较长的场景是必须的，它能有效的利用Consumer的资源，相对于Consumer端使用多线程来说开销较小；
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### 参数回调
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参数回调有点类似本地Callback机制，但Callback并不是Dubbo内部的类或接口，而是由Provider端自定义的。Dubbo将基于长连接生成反向代理，从而实现从Provider端调用Consumer端逻辑。
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### 事件通知
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事件通知允许Consumer端在调用之前、之后或出现异常时，触发oninvoke、onreturn、onthrow三个事件
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自定义Notify接口中三个方法的参数规则如下：
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1. oninvoke 方法参数与调用方法的参数相同；
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2. onreturn 方法第一个参数为调用方法的返回值，其余为调用方法的参数；
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3. onthrow 方法第一个参数为调用异常，其余为调用方法的参数；
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### Dubbo事件通知实战
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#### 1、Provider配置，创建分组
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
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xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context"
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xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
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http://dubbo.apache.org/schema/dubbo http://dubbo.apache.org/schema/dubbo/dubbo.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
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<context:property-placeholder/>
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<dubbo:application name="notify-provider"/>
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<dubbo:registry address="zookeeper://${zookeeper.address:127.0.0.1}:2181"/>
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<dubbo:protocol name="dubbo" port="20880"/>
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<bean id="demoService" class="com.ipman.dubbo.notify.sample.impl.DemoServiceImpl"/>
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<dubbo:service interface="com.ipman.dubbo.notify.sample.api.DemoService" ref="demoService" version="1.0.0"
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group="cn"/>
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</beans>
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```
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#### 2、Consumer配置，绑定分组，绑定onreturn、onthrow事件
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
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xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context"
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xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
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http://dubbo.apache.org/schema/dubbo http://dubbo.apache.org/schema/dubbo/dubbo.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
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<context:property-placeholder/>
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<dubbo:application name="notify-consumer"/>
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<dubbo:registry address="zookeeper://${zookeeper.address:127.0.0.1}:2181"/>
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<bean id="demoCallback" class="com.ipman.dubbo.notify.sample.impl.NotifyImpl"/>
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<dubbo:reference id="demoService" check="false" interface="com.ipman.dubbo.notify.sample.api.DemoService"
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version="1.0.0" group="cn">
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<!-- 绑定事件 -->
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<dubbo:method name="sayHello" async="false" onreturn="demoCallback.onReturn" onthrow="demoCallback.onThrow"/>
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</dubbo:reference>
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</beans>
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```
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#### 3、测试onreturn、onthrow事件
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```java
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public class NotifyConsumer {
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public static void main(String[] args) {
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ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring/notify-consumer.xml");
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DemoService demoService = context.getBean("demoService", DemoService.class);
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//onReturn：name=sayHello.ok，id=1
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demoService.sayHello(1);
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//onThrow：ex=java.lang.RuntimeException: runtime exception from id > 5，id=6
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demoService.sayHello(6);
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}
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}
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```

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