Spring兑现RMI调用

Spring实现RMI调用
传统的实现RMI，需要
1.服务接口必须从Remote派生，每个方法抛出RemoteException
2.实现类必须从UnicastRemoteObject派生
3.所有方法的参数和返回值，必须是基本类型，或者实现了Serializable接口

public class User implements Serializable {  private String username;  private String password;  public User(String username, String password) {    this.username = username;    this.password = password;  }  public String getUsername() {    return username;  }  public String getPassword() {    return password;  }}public interface RmiUserService extends Remote {  User login(String username, String password) throws RemoteException;  void create(String username, String password) throws RemoteException;}public class RmiUserServiceImpl extends UnicastRemoteObject implements RmiUserService {  protected RmiUserServiceImpl() throws RemoteException {  }  private Map<String, String> users = new HashMap<String, String>();  public void create(String username, String password) {    if (username == null || password == null)      throw new IllegalArgumentException("Invalid args.");    if (users.get(username) != null)      throw new RuntimeException("User exist!");    users.put(username, password);  }  public User login(String username, String password) {    if (username == null || password == null)      throw new IllegalArgumentException("Invalid args.");    if (password.equals(users.get(username)))      return new User(username, password);    throw new RuntimeException("Login failed.");  }  public static void main(String[] args) throws RemoteException, MalformedURLException, AlreadyBoundException {    LocateRegistry.createRegistry(1099);    Naming.bind("rmi://localhost:1099/UserService", new RmiUserServiceImpl());  }}public class Client {  public static void main(String[] args) throws RemoteException, MalformedURLException, NotBoundException {    RmiUserService service = (RmiUserService) Naming.lookup("rmi://localhost:1099/UserService");    service.create("xace", "1");    System.out.println(service.login("xace", "1"));  }}调用：>rmic RmiUserServiceImpl>java Client

Spring对RMI提供的支持
不用写一行代码，直接在Spring的配置文件中声明，就可以将一个传统的java类作为RMI服务输出

  <bean id="userService" />  <bean id="rmiService" value="UserService"/>    <property name="service" ref="userService"/>    <property name="serviceInterface" value="example.rmi.UserService"/>    <property name="registryPort" value="1099"/>  </bean>

唯一编写的代码是main()方法，启动Spring容器

    public static void main(String[] args) {        new ClassPathXmlApplicationContext("config.xml");    }

客户端代码

public class Client {  public static void main(String[] args) throws Exception {    RmiProxyFactoryBean factory = new RmiProxyFactoryBean();    factory.setServiceInterface(UserService.class);    factory.setServiceUrl("rmi://localhost:1099/UserService");    factory.afterPropertiesSet();    UserService service = (UserService) factory.getObject();    service.create("test", "password");    System.out.println(service.login("test", "password"));    try {      service.login("test", "bad-password");    } catch (Exception e) {      System.out.println(e.getMessage());    }  }}

如果客户端也在Spring容器中启动，完全可以在XML配置文件中定义UserService并直接使用

  <bean id="userServiceRmi" value="rmi://localhost:1099/UserService" />    <property name="serviceInterface" value="example.rmi.UserService" />  </bean>

RMI虽然是Java标准的远程调用模式，但是它使用特定的Java Remote Method Protocol二进制协议，很难穿透防火墙，如果要跨防火墙，应该使用HTTP协议为基础的远程调用。
Hessian; Burlap; Spring HTTP Invoker。使用私有协议的Http远程调用没有成为标准，实际应用较少，只能用于Java应用程序之间的远程调用。如果希望和异构平台实现远程调用，就必须使用标准的Web服务（Web Services）

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