一、题目描述

编写Java程序，实现RMI远程调用。客户端指定某个http网站，把这个网址传递给服务器端，服务器端提供http下载服务，通过http get 请求访问http网站，把对应的html文件返回给客户端

二、实现思路

1. 客户端

在GUI界面输入访问的网址，按下按钮提交请求\
监听按钮点击事件，引用远程访问的类，将处理结果反馈到文本框中

2. 服务器端

定义服务接口，需要继承自Remote类\
定义实现服务接口的类，在类中编写业务逻辑，需要继承 UnicastRemoteObject 类\
在主函数中注册服务

三、实现过程

1. 客户端

编写基本的GUI界面(不熟。。要是写前端三件套就好了

public class RMIClient extends JFrame {  
  
    public static void main(String[] args) {  
        new RMIClient("Client");  
    }  
    public RMIClient(String var){  
        super(var);  
        this.setSize(1000, 1500);  
        this.setTitle("RAMClient");  

        JPanel jp1 = new JPanel();  
        JLabel jl1 = new JLabel("Please type the URL you want to visit: ");  
        JTextField jt1 = new JTextField(30);  
        JButton jb1 = new JButton("Confirm");  
        jp1.add(jl1);  
        jp1.add(jt1);  
        jp1.add(jb1);  

        JTextArea jTextArea = new JTextArea();  
        jTextArea.setSize(250, 1200);  
        jTextArea.setEditable(false);  
        JScrollPane sp =new JScrollPane();  
        sp.setViewportView(jTextArea);

监听JButton事件，将返回数据逐行添加到JTextArea

jb1.addActionListener((e)->{  
    String input = jt1.getText();  
    File htmlFile;  
    // lookup method to find reference  
    try{  
        DownloadService access = (DownloadService) Naming.lookup("rmi://localhost:1099/download");  
        htmlFile = access.getHTMLfile(input);  
        if(htmlFile != null){  
            BufferedReader bufferedReader = new BufferedReader(new FileReader(htmlFile));  
            String temp = null;  
            while((temp = bufferedReader.readLine()) != null){  
                jTextArea.append(temp+'\n');  
                //System.out.println(temp+'\n');  
            }  
            bufferedReader.close();  
        }  
    }catch (Exception err){  
        err.printStackTrace();  
    }  
});

将组件添加到JFrame中并显示

        this.setLayout(new GridLayout(3, 4));  
        this.add(jp1);  
        this.add(sp);  
        this.setVisible(true);  
        this.pack();  
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
    }  
}

2. 服务器端

定义服务接口DownloadService

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public interface DownloadService extends Remote {  
    File getHTMLfile(String urlStr) throws RemoteException, MalformedURLException;  
}

定义实现上述接口的服务类

public class DownloadServiceImpl extends UnicastRemoteObject implements DownloadService {  
    protected DownloadServiceImpl() throws RemoteException{  
        super();  
    }

初始化Http连接对象以及响应文件对象

@Override  
public File getHTMLfile(String urlStr) throws RemoteException, MalformedURLException {  
    // initialization  
    File file = new File("result.html");  
    FileWriter fileWriter = null;  
    try {  
        if(!file.exists()){  
            file.createNewFile();  
        }  
        fileWriter = new FileWriter(file);  
    }catch (IOException e){  
        e.printStackTrace();  
    }  
    HttpURLConnection conn = null;  
    InputStream inputStream = null;  
    BufferedReader bufferedReader = null;

建立连接，逐行读取返回的HTML响应，保存到文件中

        // create connection  
        try{  
            URL url = new URL(urlStr);  
            conn = (HttpURLConnection) url.openConnection();  
            conn.setRequestMethod("GET");  
            conn.setConnectTimeout(12000);  
            conn.connect();  
            System.out.println("Wait for response");  
            if(conn.getResponseCode() == 200){  
                // if conn success  
                inputStream = conn.getInputStream();  
                if (inputStream != null){  
                    bufferedReader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"));  
                    String temp = null;  
                    while((temp = bufferedReader.readLine())!= null){  
                        fileWriter.write(temp);  
                        fileWriter.write('\n');  
                    }  
                    fileWriter.close();  
                }  
            }  
        }catch (IOException e){  
            e.printStackTrace();  
        }  
        return file;  
    }  
}

在主函数中注册服务

public class RMIServer {  
    public static void main(String[] args){  
        try{  
            DownloadService downloadService = new DownloadServiceImpl();  
            LocateRegistry.createRegistry(1099);  
            Naming.rebind("rmi://localhost:1099/download", downloadService);  
            System.out.println("Server is ready!");  
        }catch (Exception e){  
            e.printStackTrace();  
        }  
    }  
}