Dubbo是阿里巴巴公司开源的一个高性能优秀的服务框架，使得应用可通过高性能的RPC实现服务的输出和输入功能，可以和Spring框架无缝集成。
Dubbo是一款高性能、轻量级的开源Java RPC框架，它提供了三大核心能力：面向接口的远程方法调用，智能容错和负载均衡，以及服务自动注册和发现。
对于Dubbo框架中，首先要了解其中涉及的三个基本的概念：provider(服务提供方)，consumer(服务消费方)和注册中心。接下来，本文从这几个角色的角度，分别实现一个小的demo，以便尽快对于dubbo框架有一个简单的入门。
0、准备
这里们采用的IDE是macOS下的IDEA。我们新健一个名为DubboDemoProj的空Java工程，只选JDK就行，别的都不用选。
new empty project
我们将在这个工程中，新建各个Module来实现Dubbo框架中的各个角色。
1、接口依赖模块dubbo-api
dubbo-api模块提供统一的接口，最终会打为jar包，供consumer和provider引用。
这里dubbo-api模块新建的时候，要选Maven，但是不要勾选任何archetype，只需要建一个空的Maven项目就行。建好之后，结构如下图。
dubbo-api structure
dubbo-api/pom.xml是Maven的配置文件。其中，定义了该Module依赖了dubbo框架，同时为了避免Dubbo自带的Spring框架过低，我们排除掉了dubbo自带的spring框架，并显示指定了spring依赖的版本。如下。
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.spacecat.dubbo</groupId>
<artifactId>dubbo-api</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>dubbo</artifactId>
<version>2.5.3</version>
<exclusions>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring</artifactId>
</exclusion>
</exclusions>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
<version>4.2.5.RELEASE</version>
<scope>provided</scope>
</dependency>
</dependencies>
</project>
user-references.xml文件是该Module的classpath路径下提供了一个xml配置，该配置文件其实就是dubbo消费者的相关配置，后边消费者项目引入api之后可以直接使用该文件。内容如下。
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:dubbo="http://code.alibabatech.com/schema/dubbo"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://code.alibabatech.com/schema/dubbo
http://code.alibabatech.com/schema/dubbo/dubbo.xsd">
<!-- 引用服务配置 -->
<dubbo:reference id="userService" interface="com.dubbo.api.UserService" cluster="failfast" check="false"/>
</beans>
UserService.java是一个接口，他定义了统一的接口让provider和consumer来引用，内容如下。
package com.dubbo.api;
/**
* Created by chengxia on 2019/5/3.
*/
public interface UserService {
String sayHi(String name);
}
编辑完上述源码文件之后，执行mvn install命令，将这个module装到mvn的本地仓库。这样，后面的项目就能够通过这个module的坐标在Maven的pom文件中，引用到这个模块。
$ mvn install
[INFO] Scanning for projects...
[INFO]
[INFO] --------------------< com.spacecat.dubbo:dubbo-api >--------------------
[INFO] Building dubbo-api 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ dubbo-api ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 1 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ dubbo-api ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!
[INFO] Compiling 1 source file to /Users/chengxia/Developer/Java/DubboDemoProj/dubbo-api/target/classes
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ dubbo-api ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /Users/chengxia/Developer/Java/DubboDemoProj/dubbo-api/src/test/resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ dubbo-api ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ dubbo-api ---
[INFO] No tests to run.
[INFO]
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ dubbo-api ---
[INFO] Building jar: /Users/chengxia/Developer/Java/DubboDemoProj/dubbo-api/target/dubbo-api-1.0-SNAPSHOT.jar
[INFO]
[INFO] --- maven-install-plugin:2.4:install (default-install) @ dubbo-api ---
[INFO] Installing /Users/chengxia/Developer/Java/DubboDemoProj/dubbo-api/target/dubbo-api-1.0-SNAPSHOT.jar to /Users/chengxia/Developer/Java/tools/apache-maven-3.6.0/repository/com/spacecat/dubbo/dubbo-api/1.0-SNAPSHOT/dubbo-api-1.0-SNAPSHOT.jar
[INFO] Installing /Users/chengxia/Developer/Java/DubboDemoProj/dubbo-api/pom.xml to /Users/chengxia/Developer/Java/tools/apache-maven-3.6.0/repository/com/spacecat/dubbo/dubbo-api/1.0-SNAPSHOT/dubbo-api-1.0-SNAPSHOT.pom
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.537 s
[INFO] Finished at: 2019-05-05T00:45:01+08:00
[INFO] ------------------------------------------------------------------------
ChengdeMacBook-Pro:dubbo-api chengxia$
2、服务提供方模块dubbo-provider
同样是一个在DubboDemoProj中的空Maven模块，建好之后，结构如下图。
dubbo-provider structure
pom.xml文件，其中，针对上面dubbo-api模块的依赖，具体如下。
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.spacecat.dubbo</groupId>
<artifactId>dubbo-provider</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>dubbo</artifactId>
<version>2.5.3</version>
<exclusions>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
<version>4.2.5.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context-support</artifactId>
<version>4.2.5.RELEASE</version>
</dependency>
<dependency>
<groupId>com.spacecat.dubbo</groupId>
<artifactId>dubbo-api</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>org.apache.zookeeper</groupId>
<artifactId>zookeeper</artifactId>
<version>3.4.10</version>
</dependency>
<dependency>
<groupId>com.github.sgroschupf</groupId>
<artifactId>zkclient</artifactId>
<version>0.1</version>
</dependency>
</dependencies>
</project>
UserServiceImpl.java是服务的实现类，如下。
package com.dubbo.provider;
import com.dubbo.api.UserService;
/**
* Created by chengxia on 2019/5/3.
*/
public class UserServiceImpl implements UserService {
public String sayHi(String s) {
return "hello " + s + "!";
}
}
com.dubbo.provider.Main是启动dubbo服务的，内容如下。
package com.dubbo.provider;
/**
* Created by chengxia on 2019/5/3.
*/
public class Main {
public static void main(String[] args) {
com.alibaba.dubbo.container.Main.main(args);
}
}
这个类调是dubbo框架提供的方法来启动dubbo服务。dubbo会在启动服务时，会读取classpath下一个名为dubbo.properties文件的属性配置。这里我们只要按照dubbo的规则配置相关参数即可，如下：
dubbo.properties：
dubbo.container=spring
#set dubbo Sping load setting xmls
dubbo.spring.config=classpath:dubbo-provider.xml
dubbo.protocol.name=dubbo
dubbo.protocol.port=28511
dubbo.container指定了dubbo的容器使用spring，dubbo内部有四种容器实现，SpringContainer是其中一种，也是默认的容器。dubbo.spring.config指定了dubbo在启动服务时加载的spring配置文件。dubbo.protocol.name和dubbo.protocol.port分别指定使用的协议名和端口。
dubbo source example
上图是Spring源码的截图。SpringContainer类中定义了两个常量，SPRING_CONFIG和DEFAULT_SPRING_CONFIG，大概读一下代码就可以知道，start方法在执行时，会读取dubbo.spring.config属性值，该值指定的就是spring的配置文件，如果没读到，则使用默认的配置。默认配置为classpath*;META-INF/spring/*.xml，意思是读取classpath下META-INF文件夹下的spring文件夹中的所有xml文件。所以，我们也可以不配置dubbo.spring.config，但是要遵循dubbo默认的读取路径，将spring配置文件放置在META-INF/spring文件夹下。
dubbo-provider.xml是一个spring配置文件，只不过引入了dubbo相关的配置：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:dubbo="http://code.alibabatech.com/schema/dubbo"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://code.alibabatech.com/schema/dubbo
http://code.alibabatech.com/schema/dubbo/dubbo.xsd">
<dubbo:application name="dubbo-provider"/>
<dubbo:registry address="zookeeper://127.0.0.1:2181"/>
<dubbo:provider cluster="failfast"/>
<bean id="userService" class="com.dubbo.provider.UserServiceImpl"/>
<dubbo:service interface="com.dubbo.api.UserService" ref="userService"/>
</beans>
其中：
-
<dubbo:application>指定了程序名称，我们可以在dubbo管理后台中通过该名称更清晰的区分服务 -
<dubbo:registry>指定了注册中心的地址，这里用的是本地的zookeeper。 -
<dubbo:provider>指定了集群容错模式，此处为快速失败 -
<bean>普通的spring依赖注入 -
<dubbo:service>服务导出，引用<bean>标签注入的类
3、注册中心
这里的注册中心，我们使用的是zookeeper。
3.1 zookeeper安装
$ brew info zookeeper
zookeeper: stable 3.4.13 (bottled), HEAD
Centralized server for distributed coordination of services
https://zookeeper.apache.org/
Not installed
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/zookeeper.rb
==> Options
--HEAD
Install HEAD version
==> Caveats
To have launchd start zookeeper now and restart at login:
brew services start zookeeper
Or, if you don't want/need a background service you can just run:
zkServer start
==> Analytics
install: 5,018 (30 days), 14,429 (90 days), 58,577 (365 days)
install_on_request: 1,733 (30 days), 4,463 (90 days), 19,783 (365 days)
build_error: 0 (30 days)
$
执行brew安装命令：
$ brew install zookeeper
Updating Homebrew...
==> Auto-updated Homebrew!
Updated 2 taps (homebrew/core and homebrew/cask).
... ...
==> Deleted Formulae
safe
==> Downloading https://homebrew.bintray.com/bottles/zookeeper-3.4.13.mojave.bottle.tar.gz
==> Downloading from https://akamai.bintray.com/d1/d1e4e7738cd147dceb3d91b32480c20ac5da27d129905f336ba51c0c01b8a476?__gda__=exp=1556685597~hmac=2a06d1cd6581464fdc9510af3179137ee9754a2d28f1fe423eafaebf5fb6aec9&re
######################################################################## 100.0%
==> Pouring zookeeper-3.4.13.mojave.bottle.tar.gz
==> Caveats
To have launchd start zookeeper now and restart at login:
brew services start zookeeper
Or, if you don't want/need a background service you can just run:
zkServer start
==> Summary
🍺 /usr/local/Cellar/zookeeper/3.4.13: 244 files, 33.4MB
==> `brew cleanup` has not been run in 30 days, running now...
Removing: /Users/chengxia/Library/Caches/Homebrew/fontconfig--2.13.1.mojave.bottle.tar.gz... (1.2MB)
Removing: /Users/chengxia/Library/Caches/Homebrew/freetype--2.9.1.mojave.bottle.tar.gz... (874.5KB)
Removing: /Users/chengxia/Library/Caches/Homebrew/gd--2.2.5.mojave.bottle.tar.gz... (290KB)
Removing: /Users/chengxia/Library/Caches/Homebrew/jpeg--9c.mojave.bottle.tar.gz... (300.8KB)
Removing: /Users/chengxia/Library/Caches/Homebrew/libtool--2.4.6_1.mojave.bottle.tar.gz... (1003.4KB)
Removing: /Users/chengxia/Library/Logs/Homebrew/tree... (64B)
$
安装后，在/usr/local/etc/zookeeper/目录下，已经有了缺省的配置文件。查看zookeeper配置文件：
$ ls /usr/local/etc/zookeeper
defaults log4j.properties zoo.cfg zoo_sample.cfg
$
缺省配置/usr/local/etc/zookeeper/zoo.cfg 内容如下：
$ cat /usr/local/etc/zookeeper/zoo.cfg
# The number of milliseconds of each tick
tickTime=2000
# The number of ticks that the initial
# synchronization phase can take
initLimit=10
# The number of ticks that can pass between
# sending a request and getting an acknowledgement
syncLimit=5
# the directory where the snapshot is stored.
# do not use /tmp for storage, /tmp here is just
# example sakes.
dataDir=/usr/local/var/run/zookeeper/data
# the port at which the clients will connect
clientPort=2181
# the maximum number of client connections.
# increase this if you need to handle more clients
#maxClientCnxns=60
#
# Be sure to read the maintenance section of the
# administrator guide before turning on autopurge.
#
# http://zookeeper.apache.org/doc/current/zookeeperAdmin.html#sc_maintenance
#
# The number of snapshots to retain in dataDir
#autopurge.snapRetainCount=3
# Purge task interval in hours
# Set to "0" to disable auto purge feature
#autopurge.purgeInterval=1
$
3.2 zookeeper启动
启动zookeeper：
$ zkServer
ZooKeeper JMX enabled by default
Using config: /usr/local/etc/zookeeper/zoo.cfg
Usage: ./zkServer.sh {start|start-foreground|stop|restart|status|upgrade|print-cmd}
ChengdeMacBook-Pro:~ chengxia$ zkServer status
ZooKeeper JMX enabled by default
Using config: /usr/local/etc/zookeeper/zoo.cfg
Error contacting service. It is probably not running.
$ zkServer start
ZooKeeper JMX enabled by default
Using config: /usr/local/etc/zookeeper/zoo.cfg
Starting zookeeper ... STARTED
$ zkServer status
ZooKeeper JMX enabled by default
Using config: /usr/local/etc/zookeeper/zoo.cfg
Mode: standalone
$
3.3 zookeeper简单操作
查看zookeeper的运行状态：
$ zkCli
Connecting to localhost:2181
Welcome to ZooKeeper!
JLine support is enabled
WATCHER::
WatchedEvent state:SyncConnected type:None path:null
[zk: localhost:2181(CONNECTED) 0] ls
[zk: localhost:2181(CONNECTED) 1] ls /
[zookeeper]
[zk: localhost:2181(CONNECTED) 2] ls /zookeeper
[quota]
[zk: localhost:2181(CONNECTED) 3] ls /zookeeper/quota
[]
[zk: localhost:2181(CONNECTED) 4] quit
Quitting...
$
停止运行zookeeper：
$ zkServer stop
ZooKeeper JMX enabled by default
Using config: /usr/local/etc/zookeeper/zoo.cfg
Stopping zookeeper ... STOPPED
$
4、服务消费方
到这里，我们在本地启动zookeeper，然后，在IDEA中运行上面的com.dubbo.provider.Main，我们就将上面的服务注册到了本机的注册中心(zookeeper)。接下来，可以调用这个服务。
4.1 写一个简单的Spring项目来当做服务消费方
项目结构如下图。
spring-consumer structure
dubbo-consumer/pom.xml：
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.spacecat.dubbo</groupId>
<artifactId>dubbo-consumer</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<!-- Spring Core -->
<!-- http://mvnrepository.com/artifact/org.springframework/spring-core -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>4.1.4.RELEASE</version>
</dependency>
<!-- Spring Context -->
<!-- http://mvnrepository.com/artifact/org.springframework/spring-context -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>4.1.4.RELEASE</version>
</dependency>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>dubbo</artifactId>
<version>2.5.3</version>
<exclusions>
<exclusion>
<groupId>org.springframework</groupId>
<artifactId>spring</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>com.spacecat.dubbo</groupId>
<artifactId>dubbo-api</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>org.apache.zookeeper</groupId>
<artifactId>zookeeper</artifactId>
<version>3.4.10</version>
</dependency>
<dependency>
<groupId>com.github.sgroschupf</groupId>
<artifactId>zkclient</artifactId>
<version>0.1</version>
</dependency>
</dependencies>
</project>
这个Module中，依赖了dubbo-api。
dubbo-consumer.xml：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:dubbo="http://code.alibabatech.com/schema/dubbo"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://code.alibabatech.com/schema/dubbo http://code.alibabatech.com/schema/dubbo/dubbo.xsd">
<dubbo:application name="dubbo-consumer"/>
<dubbo:registry address="zookeeper://127.0.0.1:2181"/>
<dubbo:consumer check="false"/>
<!-- 导入dubbo配置，dubbo-api模块打包后自带的配置文件 -->
<import resource="classpath*:user-references.xml"/>
</beans>
这个文件中，直接引用了dubbo-api模块打包后自带的配置文件user-references.xml。
com.dubbo.consumer.UserServiceCaller：
package com.dubbo.consumer;
import com.dubbo.api.UserService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
/**
* Created by chengxia on 2019/5/5.
*/
public class UserServiceCaller {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("dubbo-consumer.xml");
UserService service = (UserService) context.getBean("userService");
System.out.print("Got service bean:");
System.out.println(service);
System.out.println("RPC call output:");
System.out.println(service.sayHi("Kobe"));
}
}
该文件完成了对服务的调用，可见dubbo框架已经把服务注入到一个本地可以直接调用的bean中了。直接调用bean的方法即可完成对于服务的远程调用(其实，已经和调本地一样了)。
启动zookeeper，运行前面的dubbo-provider模块中的启动类，然后再运行com.dubbo.consumer.UserServiceCaller，可以得到如下输出。
log4j:WARN No appenders could be found for logger (org.springframework.core.env.StandardEnvironment).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Got service bean:com.alibaba.dubbo.common.bytecode.proxy0@49dc7102
RPC call output:
hello Kobe!
Process finished with exit code 0
4.2 通过命令行调用服务
通过命令行调用服务适用于对dubbo服务做个简单的测试的情况。可以直接在命令行通过telnet的方式来查看和调用dubbo服务。
新版本的MacOS默认没有telnet，可以通过如下步骤安装。
4.2.1 MacOS安装telnet
$ telnet
-bash: telnet: command not found
$ brew install telnet
Updating Homebrew...
==> Auto-updated Homebrew!
Updated 2 taps (homebrew/core and homebrew/cask).
==> New Formulae
pipx
==> Updated Formulae
allureofthestars bluepill dovecot glib-networking gupnp mercurial php@7.2 pulumi qt translate-shell
bettercap bzt faas-cli gmic hugo pdftoipe poppler pumba taskell
bit diff-pdf ghq gssdp imagemagick@6 php prototool pushpin tmux
==> Deleted Formulae
node@6
==> Downloading https://homebrew.bintray.com/bottles/telnet-60.mojave.bottle.tar.gz
######################################################################## 100.0%
==> Pouring telnet-60.mojave.bottle.tar.gz
🍺 /usr/local/Cellar/telnet/60: 4 files, 138.2KB
ChengdeMacBook-Pro:~ chengxia$ telnet
telnet> quit
$
4.2.2 通过telnet查看和调用dubbo服务。
方法如下示例，这里的端口就是前面dubbo-provider模块中dubbo.properties文件中配置的端口，这个端口应该就是服务提供方的端口。
$ telnet 127.0.0.1 28511
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
ls
com.dubbo.api.UserService
dubbo>invoke com.dubbo.api.UserService.sayHi("Kobe")
"hello Kobe!"
elapsed: 1 ms.
dubbo>
