实现协议处理框架

本节将为用户自定义的 ECHO 协议实现处理框架，共创建了以下类：

• EchoURLConnection 类：继承自 URLConnection 类
• EchoURLStreamHandler 类：继承自 URLStreamHandler 类
• EchoURLStreamHandlerFactory 类：实现 URLStreamHandlerFactory 接口
• EchoContentHandler 类：继承自 ContentHandler 类
• EchoContentHandlerFactory 类：实现 ContentHandlerFactory 接口

1. 创建 EchoURLConnection 类

EchoURLConnection 类封装了一个 Socket，在 connect() 方法中创建与远程服务器连接的 Socket 对象

public class EchoURLConnection extends URLConnection {
    
    private Socket connection = null;
    public final static int DEFAULT PORT = 8000;
    
    public EchoURLConnection(URL url) {
        super(url);
    }
    
    public synchronized InputStream getInputStream() throws IOException {
        if(!connected) connect();
        return connection.getInputStream();
    }
    
    public synchronized OutputStream getOutputStream() throws IOException {
        if(!connected) connect();
        return connection.getOutputStream();
    }
    
    public String getContentType() {
        return "text/plain";
    }
    
    public synchronized void connect() throws IOException {
        if(!connected) {
            int port = url.getPort();
            if(port < 0 || port > 65535) port = DEFAULT_PORT;
            this.connection = new Socket(url.getHost(), port);
            this.connected = true;
        }
    }
    
    public synchronized void disconnect() throws IOException {
        if(connected) {
            //断开连接
            this.connection.close();
            this.connected = false;
        }
    }
}

2. 创建 EchoURLStreamHandler 及工厂类

EchoURLStreamHandler 类的 openConnection() 方法负责创建一个 EchoURLConnection 对象

public class EchoURLStreamHandler extends URLStreamHandler {
    
    public int getDefaultPort() {
        return 8000;
    }
    
    protected URLConnection openConnection(URL url) throws IOException {
        return new EchoURLConnection(url);
    }
}

EchoURLStreamHandlerFactory 类的 createURLStreamHandle() 方法负责构造 EchoURLStreamHandler 实例

public class EchoURLStreamHandlerFactory implements URLStreamhandlerFactory {
    
    public URLStreamHandler createURLStreamHandler(String protocol) {
        if(protocol.equals("echo"))
            return new EchoURLStreamHandler();
        else
            return null;
    }
}

在客户程序中，可以通过以下方式设置 EchoURLStreamHandlerFactory

URL.setURLStreamHandlerFactory(new EchoURLStreamHandlerFactory());
URL url=new URL("echo://localhost:8000");

3. 创建 EchoContentHandler 类及工厂类

URLConnection 类还提供了 getContent() 方法，它有两种重载形式：

public Object getContent();
public Object getContent(Class[] classes);

第二个 getContent() 方法把服务器发送的数据优先转换为 classes 数组第一个元素指定的类型，如果转换失败，再尝试转换第二个元素指定的类型，以此类推

下例 HttpClient 演示处理服务器发送的数据

public class HttpClient {
    
    public static void main(String args[]) throws IOException {
        URL url = new URL("http://www,javathinker.net/hello.htm");
        URlConnection connection = url.openConnection();
        //接收响应结果
        InputStream in = connection.getInputStream();
        Class[] types = {String.class, InputStream.class};
        Object obj = connection.getContent(types);
        
        if(obj instanceof String) {
            System.out.println(obj);
        } else if(obj instanceof InputStream) {
            in = (InputStream) obj;
            FileOutputStream file = new FileOutputStream("data");
            byte[] buff = new byte[1024];
            int len = -l;
            
            while((len = in.read(buff)) != -1) {
                file.write(buff, 0 ,len);
            }
            
            System.out.println("正文保存完毕");
        } else {
            System.out.println("未知的响应正文类型");
        }
    }
}