一、先说一个结论：单元测试与主项目的spring容器是隔离的，也就是说，单元测试无法访问主项目spring容器，需要自己加载spring容器。

接下来是代码实例，WEB主项目出于运行状态，单元测试中可能会看到如下这样的代码：

代码一：当前类加载式

public class TestSpring {

    @Test

    public void testSpring(){

        LoginService loginService = this.getBean("loginService");

    }

    //以下为容器实例声明及初始化、销毁

    private ClassPathXmlApplicationContext context;

    @Before

    public void before(){

        //加载spring容器

        context = new ClassPathXmlApplicationContext("spring-context.xml");

    }

    @After

    public void after(){

        context.destroy();

    }

    //从静态变量applicationContext中取得Bean, 自动转型为所赋值对象的类型.

    public <T> T getBean(String name) {

        return (T) context.getBean(name);

    }

    //从静态变量applicationContext中取得Bean, 自动转型为所赋值对象的类型.

    public <T> T getBean(Class<T> requiredType) {

        return context.getBean(requiredType);

    }

}

代码二：继承加载式

/**

 * @Description: 登录单元测试类

 */

public class LoginTest extends SpringJunitSupport{

    @Autowired

    private LoginService loginService;

    @Test

    public void testLogin(){

        loginService.login();

    }

//让单元测试运行于spring环境，保证拥有spring框架相关支持

@RunWith(SpringJUnit4ClassRunner.class)

//加载spring容器

@ContextConfiguration("classpath:/spring-context.xml")

public class SpringJunitSupport {

}

代码三：动态添加spring配置文件式

/**

 * @Description: 登录单元测试类

 */

public class LoginTest{

    //使用@Before注解方式加载spring容器配置文件，就不能通过自动装配的方式注入bean，因为自动装配注解执行要早于@Before

    //@Autowired

    private LoginService loginService;

    private TestSpringContextSupport springContextSupport = null;

    @Before

    public void setUp() throws Exception {

        springContextSupport = new TestSpringContextSupport();

        //初始化spring容器时，再动态添加spring bean配置文件

        springContextSupport.init(new String[] { "classpath:/support-quartz.xml" });

        loginService = springContextSupport.getBean("loginService");

    }

    @Test

    public void testLogin(){

        loginService.login();

    }

}

public class TestSpringContextSupport {

    //通过静态语句块初始化一个静态变量，用于存放spring容器配置文件

    public static List<String> contextList = new ArrayList<String>();

    static {

        contextList.add("classpath:/spring-context.xml");

    }

    private ApplicationContext context;

    //定义初始化方法，动态添加spring配置文件到静态配置文件集合

    public void init(String[] contextFile) {

        List<String> list = new ArrayList<String>();

        list.addAll(contextList);

        for (int i = 0; contextFile != null && i < contextFile.length; i++) {

            list.add(contextFile[i]);

        }

        String[] x = new String[list.size()];

        list.toArray(x);

        //加载spring容器

        context = new ClassPathXmlApplicationContext(x);

    }

    //从静态变量applicationContext中取得Bean, 自动转型为所赋值对象的类型.

    public <T> T getBean(String name) {

        return (T) context.getBean(name);

    }

    //从静态变量applicationContext中取得Bean, 自动转型为所赋值对象的类型.

    public <T> T getBean(Class<T> requiredType) {

        return context.getBean(requiredType);

    }

}

如上面三种方式，有一个共同点，就是在单元测试方法执行前，都大费周章的去加载了spring容器。 
web主项目出于运行状态，单元测试为什么还要单独加载spring容器，因为web主项目的spring容器对单元测试是隔离的，通过如下手段验证：

验证1：

把单元测试所有加载spring容器的代码去掉，保证主项目出于运行状态，通过@Autowired注解(@Autowired注解可以装配spring内部bean)，获取spring应用上下文的bean，然后再通过其获取业务bean，代码如下：

/**

 * @Description: 登录单元测试类

 */

public class LoginTest{

    //自动装配spring应用上下文bean

    @Autowired

    private ApplicationContext context;

    @Test

    public void testLogin(){

        //通过应用上下文bean，获取业务bean

        LoginService loginService = (LoginService)context.getBean("loginService");

        loginService.login();

    }

}

结果一定是空指针异常，context对象为null。

验证二，把web主项目停掉，单元测试使用上面第二种继承的方式加载spring容器，其它同上，代码如下：

/**

 * @Description: 登录单元测试类，继承SpringJunitSupport加载spring容器

 */

public class LoginTest extends SpringJunitSupport{

    //自动装配spring应用上下文bean

    @Autowired

    private ApplicationContext context;

    @Test

    public void testLogin(){

        //通过应用上下文bean，获取业务bean

        LoginService loginService = (LoginService)context.getBean("loginService");

        loginService.login();

    }

}

@RunWith(SpringJUnit4ClassRunner.class)

//加载spring容器

@ContextConfiguration("classpath:/spring-context.xml")

public class SpringJunitSupport {

}

结果一切正常，如此就验证了单元测试与主项目的spring容器是隔离的，单元测试必须自己加载spring容器。

上面一直在说加载spring容器，其实就是加载配置文件，把配置文件里面的bean加载到spring容器中，上面的验证也一直通过在spring容器中搜索bean对象进行的，理解并应用这一点是非常重要的。

最后的彩蛋，理解是因为项目中有困惑，探究之后才能领悟透彻，比如一个实例：

1、主项目运行，提供服务接口，采用的方式为dubbo+zookeeper方式；

2、单元测试，调用提供者提供的服务，采用继承式加载spring配置文件；

3、抛出异常：地址已经被绑定使用(Address already in use: bind)

java.lang.IllegalStateException: Failed to load ApplicationContext

......

Caused by: com.alibaba.dubbo.rpc.RpcException: Fail to start server(url: dubbo://127.0.0.1:20880/......

......

Caused by: com.alibaba.dubbo.remoting.RemotingException: Failed to bind NettyServer on /127.0.0.1:20880, cause: Failed to bind to: /0.0.0.0:20880

......

Caused by: org.jboss.netty.channel.ChannelException: Failed to bind to: /0.0.0.0:20880

......

Caused by: java.net.BindException: Address already in use: bind

......

4、异常原因：因为采用的是dubbo+zookeeper方式，主项目spring提供者注册了127.0.0.1:20880，单元测试加载spring配置文件想要注册0.0.0.0:20880地址，但是20880已经被主容器占用，所以单元测试无法正常加载。

5、解决办法：将主容器停掉，单独使用单元测试，即作为服务端又作为客户端

6、再次抛出异常：

DEBUG [2016-08-18 18:30:26,603] - ZkClient.java                            () - Closing ZkClient...

INFO  [2016-08-18 18:30:26,603] - ZkEventThread.java                       () - Terminate ZkClient event thread.

DEBUG [2016-08-18 18:30:26,603] - ZkConnection.java                        () - Closing ZooKeeper connected to 119.254.166.167:2181

DEBUG [2016-08-18 18:30:26,603] - ZooKeeper.java                           () - Closing session: 0x15678a538f900ef

DEBUG [2016-08-18 18:30:26,603] - ClientCnxn.java                          () - Closing client for session: 0x15678a538f900ef

......

DEBUG [2016-08-18 18:30:26,808] - ZkClient.java                            () - Closing ZkClient...done

INFO  [2016-08-18 18:30:26,810] - DubboProtocol.java                       () -  [DUBBO] Close dubbo server: /127.0.0.1:20880, dubbo version: 2.5.4, current host: 127.0.0.1

INFO  [2016-08-18 18:30:26,812] - AbstractServer.java                      () -  [DUBBO] Close NettyServer bind /0.0.0.0:20880, export /127.0.0.1:20880, dubbo version: 2.5.4, current host: 127.0.0.1

INFO  [2016-08-18 18:30:26,812] - ClientCnxn.java                          () - EventThread shut down for session: 0x15678a538f900ef

ERROR [2016-08-18 18:30:26,813] - FailbackRegistry.java                    () -  [DUBBO] Failed to uregister dubbo://127.0.0.1:20880/......

com.alibaba.dubbo.rpc.RpcException: Failed to unregister dubbo://127.0.0.1:20880/业务方法......

    at com.alibaba.dubbo.registry.zookeeper.ZookeeperRegistry.doUnregister(ZookeeperRegistry.java:108)

    at com.alibaba.dubbo.registry.support.FailbackRegistry.unregister(FailbackRegistry.java:160)

    at com.alibaba.dubbo.registry.integration.RegistryProtocol$1.unexport(RegistryProtocol.java:130)

    at com.alibaba.dubbo.config.ServiceConfig.unexport(ServiceConfig.java:270)

    at com.alibaba.dubbo.config.spring.ServiceBean.destroy(ServiceBean.java:255)

    at org.springframework.beans.factory.support.DisposableBeanAdapter.destroy(DisposableBeanAdapter.java:258)

    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroyBean(DefaultSingletonBeanRegistry.java:538)

    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingleton(DefaultSingletonBeanRegistry.java:514)

    at org.springframework.beans.factory.support.DefaultListableBeanFactory.destroySingleton(DefaultListableBeanFactory.java:831)

    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingletons(DefaultSingletonBeanRegistry.java:483)

    at org.springframework.context.support.AbstractApplicationContext.destroyBeans(AbstractApplicationContext.java:923)

    at org.springframework.context.support.AbstractApplicationContext.doClose(AbstractApplicationContext.java:897)

    at org.springframework.context.support.AbstractApplicationContext$1.run(AbstractApplicationContext.java:811)

Caused by: java.lang.NullPointerException

    at org.I0Itec.zkclient.ZkClient$8.call(ZkClient.java:720)

    at org.I0Itec.zkclient.ZkClient.retryUntilConnected(ZkClient.java:675)

    at org.I0Itec.zkclient.ZkClient.delete(ZkClient.java:716)

    at com.alibaba.dubbo.remoting.zookeeper.zkclient.ZkclientZookeeperClient.delete(ZkclientZookeeperClient.java:57)

    at com.alibaba.dubbo.registry.zookeeper.ZookeeperRegistry.doUnregister(ZookeeperRegistry.java:106)

    ... 12 more

上面需要注意的关键信息可以归结为：zookeeper客户端关闭(Closing ZkClient…)、dubbo服务关闭(Close dubbo server….)、注销dubbo的某个方法失败(Failed to uregister dubbo://127.0.0.1:20880/…) 
虽然没细探究到底怎么回事，但是感觉应该是单元测试同时加载服务端和客户端(即加载spring配置文件)，当测试方法执行完毕需要关闭服务的时候，由于先后顺序问题引发的异常。

7、再次解决办法：提供者由主容器启动，至于单元测试，就到了上面最后的彩蛋那句话了，单元测试作为客户端，只需要拿到服务端提供者的bean对象，就可以完成对提供者服务端的调用。

那么这个对象从哪里来，dubbo+zookeeper方式会在客户端配置订阅服务的配置文件，这个里面有提供者对应的bean，所以单元测试只需要加载客户端订阅配置文件即可，代码如下：

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration({ "classpath:/spring/test-dubbo-consumer.xml" })

public class CodeRuleRPCImplDubboTest {

    @Autowired

    private UserRPC UserRPC;

    @Test

    public void testGetUserByCode() {

        bizCode = userRPC.getUserByCode("001");

    }

}

客户端订阅者配置文件：

<?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:context="http://www.springframework.org/schema/context"

    xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:jee="http://www.springframework.org/schema/jee"

    xmlns:tx="http://www.springframework.org/schema/tx" xmlns:util="http://www.springframework.org/schema/util"

    xmlns:task="http://www.springframework.org/schema/task" xmlns:dubbo="http://code.alibabatech.com/schema/dubbo"

    xsi:schemaLocation="

        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd

        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd

        http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-4.0.xsd

        http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-4.0.xsd

        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd

        http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.0.xsd

        http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-4.0.xsd

        http://code.alibabatech.com/schema/dubbo http://code.alibabatech.com/schema/dubbo/dubbo.xsd">

    <!-- 消费方应用名称信息，这个相当于起一个名字，我们dubbo管理页面比较清晰是哪个应用暴露出来的 -->

    <dubbo:application name="SPRING_DUBBO_CONSUMER"></dubbo:application>

    <!-- 使用zookeeper注册中心暴露服务地址 -->

    <dubbo:registry address="zookeeper://127.0.0.1:2181"

        check="true"></dubbo:registry>

    <!-- 要引用的用户管理服务 -->

    <dubbo:reference interface="com.test.rpc.UserRPC"

        id="userRPC"></dubbo:reference>

</beans>

至此以上问题解决，同时深入理解spring容器，单元测试，spring-bean之间的关系，同时也对dubbo和zookeeper加深了了解。