通过GWT RPC实现客户端与服务器端的交互

GWT有两种与服务端进行交互的技术：GWT RPC和基于普通AJAX的远程交互技术。这里只介绍GWT RPC技术。

一个完整的RPC服务至少包含三个Java文件：

     1、客户端远程接口类，需要继承RemoteService类

     2、客户端远程接口类的异步类，异步类的名称格式是： 客户端远程接口类名 + Async 后缀

     3、服务器端的远程接口类，需要继承RemoteServiceServlet类和实现客户端远程接口类

    

     客户端相关的类必须位于client包及其子包下，服务器端相关的类必须位于server包及其子包下。

1、客户端远程接口类 源码

/**
 * 客户端远程接口类需要继承RemoteService类
 */
public interface PersonService extends RemoteService {
    public Person getPerson(String name, int age) throws RuntimeException;

    //使用内部类创建客户端远程接口类的异步类
    public static class Utils{
        private static PersonServiceAsync serviceAsync;

        public static PersonServiceAsync getInstance(){
            if(serviceAsync==null){
                serviceAsync = (PersonServiceAsync) GWT.create(PersonService.class);
            }
            return serviceAsync;
        }
    }
}

/**
 * 客户端远程接口类需要继承RemoteService类
 */
public interface PersonService extends RemoteService {
	public Person getPerson(String name, int age) throws RuntimeException;
	
	//使用内部类创建客户端远程接口类的异步类
	public static class Utils{
		private static PersonServiceAsync serviceAsync;
		
		public static PersonServiceAsync getInstance(){
			if(serviceAsync==null){
				serviceAsync = (PersonServiceAsync) GWT.create(PersonService.class);
			}
			return serviceAsync;
		}
	}
}

2、客户端远程接口类的异步类 源码

/**
 * 异步接口的方法返回值均为void，并且其对应的每个方法都比原接口多一个类型为AsyncCallback的参数
 */
public interface PersonServiceAsync {
    public void getPerson(String name, int age, AsyncCallback callback) throws RuntimeException;
}

/**
 * 异步接口的方法返回值均为void，并且其对应的每个方法都比原接口多一个类型为AsyncCallback的参数
 */
public interface PersonServiceAsync {
	public void getPerson(String name, int age, AsyncCallback callback) throws RuntimeException;
}

3、服务器端的远程接口类 源码

/**
 * 实现类要继承RemoteServiceServlet类
 */
public class PersonServiceImpl extends RemoteServiceServlet implements PersonService {
    public Person getPerson(String name, int age) throws RuntimeException {
        //与HTTP的交互
        HttpServletRequest request = this.getThreadLocalRequest();
        HttpServletResponse response = this.getThreadLocalResponse();
        HttpSession session = request.getSession();

        return new Person(name, age);
    }
}

/**
 * 实现类要继承RemoteServiceServlet类
 */
public class PersonServiceImpl extends RemoteServiceServlet implements PersonService {
	public Person getPerson(String name, int age) throws RuntimeException {
		//与HTTP的交互
		HttpServletRequest request = this.getThreadLocalRequest();
		HttpServletResponse response = this.getThreadLocalResponse();
		HttpSession session = request.getSession();
		
		return new Person(name, age);
	}
}

4、交互过程中传递的对象

/**
 * 在GWT RPC中，如果要交互的数据（方法的参数和返回值）是一个复杂类型的话，
 * 那么这个类要实现IsSerializable接口，来使该类能被正常序列化和反序列化。
 */
public class Person implements IsSerializable {
    private String name;
    private int age;

    public Person(){

    }

    public Person(String name, int age){
        this.name = name;
        this.age = age;
    }

    //省略getter、setter方法
}

/**
 * 在GWT RPC中，如果要交互的数据（方法的参数和返回值）是一个复杂类型的话，
 * 那么这个类要实现IsSerializable接口，来使该类能被正常序列化和反序列化。
 */
public class Person implements IsSerializable {
	private String name;
	private int age;
	
	public Person(){
		
	}
	
	public Person(String name, int age){
		this.name = name;
		this.age = age;
	}
	
	//省略getter、setter方法
}

5、GWT应用入口点类需要实现EntryPoint接口，其源码如下

public class Index implements EntryPoint {
    public void onModuleLoad() {
        Button button = new Button("Click me");

        VerticalPanel vPanel = new VerticalPanel();
        vPanel.setWidth("100%");
        vPanel.setHorizontalAlignment(VerticalPanel.ALIGN_CENTER);
        vPanel.add(button);

        RootPanel.get().add(vPanel);

        //按钮的单击事件
        button.addClickListener(new ClickListener() {
            public void onClick(Widget sender) {
                //初始化Service接口
                PersonServiceAsync personService = PersonService.Utils.getInstance();

                //为Service代理描述Service接入点的URL
                ServiceDefTarget target = (ServiceDefTarget)personService;
                String path = GWT.getModuleBaseURL() + "PersonService";
                target.setServiceEntryPoint(path);

                //发出RPC请求
                personService.getPerson("cjm", 100, new AsyncCallback(){
                    public void onSuccess(Object result) {
                        Person person = (Person)result;
                        Window.alert(person.getName());
                    }

                    public void onFailure(Throwable caught) {
                        Window.alert(caught.getMessage());
                    }
                });

            }
        });

    }
}

public class Index implements EntryPoint {
	public void onModuleLoad() {
		Button button = new Button("Click me");
    
		VerticalPanel vPanel = new VerticalPanel();
		vPanel.setWidth("100%");
		vPanel.setHorizontalAlignment(VerticalPanel.ALIGN_CENTER);
		vPanel.add(button);

		RootPanel.get().add(vPanel);
		
		//按钮的单击事件
		button.addClickListener(new ClickListener() {
			public void onClick(Widget sender) {
				//初始化Service接口
				PersonServiceAsync personService = PersonService.Utils.getInstance();
        
				//为Service代理描述Service接入点的URL
				ServiceDefTarget target = (ServiceDefTarget)personService;
				String path = GWT.getModuleBaseURL() + "PersonService";
				target.setServiceEntryPoint(path);
        
				//发出RPC请求
				personService.getPerson("cjm", 100, new AsyncCallback(){
					public void onSuccess(Object result) {
						Person person = (Person)result;
						Window.alert(person.getName());
					}
					
					public void onFailure(Throwable caught) {
						Window.alert(caught.getMessage());
					}
				});
        
			}
		});
		
	}
}

6、在Index.gwt.xml文件中增加以下配置信息

    将RPC服务与GWT应用入口点类关联起来

<servlet path="/PersonService" class="com.cjm.server.PersonServiceImpl"/>

<servlet path="/PersonService" class="com.cjm.server.PersonServiceImpl"/>

7、在web.xml文件增加以下配置信息

<!-- 在宿主模式下启动应用时，此servlet是必须的 -->
<servlet>
    <servlet-name>shell</servlet-name>
    <servlet-class>com.google.gwt.dev.shell.GWTShellServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>shell</servlet-name>
    <url-pattern>/*</url-pattern>
</servlet-mapping>

<!-- RPC服务配置 -->
<servlet>
    <servlet-name>PersonService</servlet-name>
    <servlet-class>com.cjm.server.PersonServiceImpl</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>PersonService</servlet-name>
    <url-pattern>/PersonService</url-pattern>
</servlet-mapping>