Java之Socket

• 介绍

网络编程是Java中很重要的一块，实现的是应用层的网络协议。本文介绍如何使用socket开发，包括有TCP和UDP的代码实现。 关于UDP广播相关的内容，可以点击这里查看另外一篇文章。 普通的Socket是使用明文来传输的，那怎么才能加密这个传输通道呢？赶快下面的例子吧。

• TCP

下面的代码实现一个服务端监听，然后打印接收到的字符串数据，最后再给客户端返回一个字符串。 [codesyntax lang="java"]

1/**
2 * http://surenpi.com
3 */
4package org.suren.test;
5
6import java.io.InputStream;
7import java.io.OutputStream;
8import java.net.ServerSocket;
9import java.net.Socket;
10import java.net.SocketAddress;
11
12/**
13 * @author suren
14 * @date 2015年9月2日 上午8:09:54
15 */
16public class TcpServer
17{
18	public static void main(String[] args) throws Exception
19	{
20		ServerSocket server = null;
21		
22		try
23		{
24			server = new ServerSocket(8090);
25			
26			while(true)
27			{
28				Socket client = server.accept();
29				
30				SocketAddress remoteAddr = client.getRemoteSocketAddress();
31				InputStream input = client.getInputStream();
32				OutputStream output = client.getOutputStream();
33				
34				System.out.println(remoteAddr);
35				
36				byte[] buf = new byte[1024];
37				int length = -1;
38				
39				StringBuffer stringBuf = new StringBuffer();
40				while((length = input.read(buf)) > 0)
41				{
42					stringBuf.append(new String(buf, 0, length));
43					
44					if(length < buf.length)
45					{
46						break;
47					}
48				}
49				
50				System.out.println(stringBuf.toString());
51				
52				output.write("done".getBytes());
53				
54				System.out.println("server round over.");
55				
56				client.close();
57			}
58		}
59		finally
60		{
61			if(server != null)
62			{
63				server.close();
64				
65				System.out.println("server closed.");
66			}
67		}
68	}
69}

[/codesyntax] 下面是客户端的实现： [codesyntax lang="java"]

1/**
2 * http://surenpi.com
3 */
4package org.suren.test;
5
6import java.io.IOException;
7import java.io.InputStream;
8import java.io.OutputStream;
9import java.net.InetSocketAddress;
10import java.net.Socket;
11import java.net.SocketAddress;
12
13/**
14 * @author suren
15 * @date 2015年9月2日 上午8:14:42
16 */
17public class TcpClient
18{
19
20	/**
21	 * @param args
22	 * @throws IOException 
23	 */
24	public static void main(String[] args) throws IOException
25	{
26		Socket client = new Socket();
27
28		SocketAddress addr = new InetSocketAddress("127.0.0.1", 8090);
29		
30		client.connect(addr);
31		
32		InputStream input = client.getInputStream();
33		OutputStream output = client.getOutputStream();
34		
35		output.write("hello from client".getBytes());
36		
37		byte[] buf = new byte[1024];
38		int length = -1;
39		
40		System.out.println("client write over.");
41		
42		StringBuffer stringBuf = new StringBuffer();
43		while((length = input.read(buf)) > 0)
44		{
45			stringBuf.append(new String(buf, 0, length));
46			
47			if(length < buf.length)
48			{
49				break;
50			}
51		}
52		
53		System.out.println(stringBuf.toString());
54		
55		client.close();
56	}
57
58}

[/codesyntax]

• UDP

这里首先要提醒的是，UDP协议是不保证数据传输的完整性的，所以说如果对数据完整性要求很高的话，不建议采用这种协议。UDP相比TCP的优点是传输效率高，可以用在视频传输上。 [codesyntax lang="java"]

1/**
2 * http://surenpi.com
3 */
4package org.suren.test;
5
6import java.io.IOException;
7import java.net.DatagramPacket;
8import java.net.DatagramSocket;
9
10/**
11 * @author suren
12 * @date 2015年9月2日 上午9:44:39
13 */
14public class UdpServer
15{
16
17	/**
18	 * @param args
19	 * @throws IOException 
20	 */
21	public static void main(String[] args) throws IOException
22	{
23		try(DatagramSocket server = new DatagramSocket(9999))
24		{
25			while(true)
26			{
27				int length = 1024;
28				byte[] buf = new byte[length];
29				DatagramPacket packet = new DatagramPacket(buf, length);
30				
31				server.receive(packet);
32				
33				System.out.println("receive from client.");
34				
35				buf = packet.getData();
36				
37				System.out.println(new String(buf, packet.getOffset(), packet.getLength()));
38
39				packet.setData("server replly".getBytes());
40				server.send(packet);
41			}
42		}
43	}
44}

[/codesyntax] 以下是客户端代码（理论上udp是没有客户端和服务端之分的，从下面的代码就可以看出来，客户端和服务端没什么区别）： [codesyntax lang="java"]

1/**
2 * http://surenpi.com
3 */
4package org.suren.test;
5
6import java.io.IOException;
7import java.net.DatagramPacket;
8import java.net.DatagramSocket;
9import java.net.InetSocketAddress;
10
11/**
12 * @author suren
13 * @date 2015年9月2日 上午9:51:40
14 */
15public class UdpClient
16{
17	public static void main(String[] args) throws IOException
18	{
19		try(DatagramSocket client = new DatagramSocket())
20		{
21			byte[] buf = "hello from udp client message.".getBytes();
22			int length = buf.length;
23			DatagramPacket packet = new DatagramPacket(buf, length);
24			packet.setSocketAddress(new InetSocketAddress("localhost", 9999));
25			
26			client.send(packet);
27			
28			client.receive(packet);
29			
30			System.out.println(new String(packet.getData(), packet.getOffset(), packet.getLength()));
31		}
32	}
33}

[/codesyntax]

• 安全的TCP

上面介绍的TCP连接，发送的都是明文的数据，通过数据包拦截工具就可以完全看到发送和接收的内容。当然，我们可以通过把要发送的数据先做加密，然后再发送。这就需要自己来编写加密和解密的逻辑了，安全性完全在于你的加密算法。另外，我们还可以使用SSL的TCP连接来发送明文或者密文数据，这是一种可以和普通TCP连接无缝对接的方式——和上面的写法几乎完全一样，只是在获取Socket的方式上有所区别。 既然是一种安全的通讯方式，肯定少不了相应的机制了。我们这里需要 使用keytool工具来生成一个证书文件，下面的代码中会用到。 下面是服务端代码： [codesyntax lang="java"]

1/**
2 * http://surenpi.com
3 */
4package org.suren.test;
5
6import java.io.File;
7import java.io.FileInputStream;
8import java.io.IOException;
9import java.io.InputStream;
10import java.io.OutputStream;
11import java.net.Socket;
12import java.security.KeyManagementException;
13import java.security.KeyStore;
14import java.security.KeyStoreException;
15import java.security.NoSuchAlgorithmException;
16import java.security.SecureRandom;
17import java.security.UnrecoverableKeyException;
18import java.security.cert.CertificateException;
19import java.security.cert.X509Certificate;
20
21import javax.net.ssl.KeyManagerFactory;
22import javax.net.ssl.SSLContext;
23import javax.net.ssl.SSLServerSocket;
24import javax.net.ssl.SSLServerSocketFactory;
25import javax.net.ssl.TrustManager;
26import javax.net.ssl.X509TrustManager;
27
28/**
29 * @author suren
30 * @date 2015年9月2日 上午10:11:54
31 */
32public class SSLTcpServer
33{
34
35	/**
36	 * @param args
37	 * @throws KeyStoreException 
38	 * @throws IOException 
39	 * @throws CertificateException 
40	 * @throws NoSuchAlgorithmException 
41	 * @throws UnrecoverableKeyException 
42	 * @throws KeyManagementException 
43	 */
44	public static void main(String[] args) throws KeyStoreException, NoSuchAlgorithmException, CertificateException, IOException, UnrecoverableKeyException, KeyManagementException
45	{
46		//证书加载
47		char[] pwd = "123456".toCharArray();
48		KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
49		
50		try(InputStream input = new FileInputStream(new File("D:/suren")))
51		{
52			keyStore.load(input, pwd);
53		}
54		
55		KeyManagerFactory keyMgr = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
56		keyMgr.init(keyStore, pwd);
57		
58		//初始化ssl上下文
59	    X509TrustManager x509m = new X509TrustManager(){
60
61			@Override
62			public void checkClientTrusted(X509Certificate[] chain,
63					String authType) throws CertificateException
64			{
65				System.out.println("checkClientTrusted");
66			}
67
68			@Override
69			public void checkServerTrusted(X509Certificate[] chain,
70					String authType) throws CertificateException
71			{
72				System.out.println("checkServerTrusted");
73			}
74
75			@Override
76			public X509Certificate[] getAcceptedIssuers()
77			{
78				System.out.println("getAcceptedIssuers");
79				return null;
80			}
81		};
82	    
83		SSLContext sslContext = SSLContext.getInstance("SSL");
84		sslContext.init(keyMgr.getKeyManagers(),
85				new TrustManager[]{x509m},
86				new SecureRandom());
87		
88		SSLServerSocketFactory factory = sslContext.getServerSocketFactory();
89		
90		try(SSLServerSocket server = (SSLServerSocket) factory.createServerSocket(8900))
91		{
92			System.out.println("ssl server socket created.");
93			
94			while(true)
95			{
96				try(Socket client = server.accept())
97				{
98					InputStream input = client.getInputStream();
99					OutputStream output = client.getOutputStream();
100					
101					StringBuffer strBuf = new StringBuffer();
102					
103					int length = 1024;
104					byte[] buf = new byte[length];			
105					
106					while((length = input.read(buf)) > 0)
107					{
108						strBuf.append(new String(buf, 0, length));
109						
110						if(length < buf.length)
111						{
112							break;
113						}
114					}
115					
116					System.out.println(strBuf.toString());
117					
118					output.write("ssl server say done.".getBytes());
119				}
120			}
121		}
122	}
123}

[/codesyntax] 下面是客户端代码： [codesyntax lang="java"]

1/**
2 * http://surenpi.com
3 */
4package org.suren.test;
5
6import java.io.IOException;
7import java.io.InputStream;
8import java.io.OutputStream;
9import java.net.UnknownHostException;
10import java.security.KeyManagementException;
11import java.security.KeyStoreException;
12import java.security.NoSuchAlgorithmException;
13import java.security.SecureRandom;
14import java.security.UnrecoverableKeyException;
15import java.security.cert.CertificateException;
16import java.security.cert.X509Certificate;
17
18import javax.net.ssl.SSLContext;
19import javax.net.ssl.SSLSocket;
20import javax.net.ssl.SSLSocketFactory;
21import javax.net.ssl.TrustManager;
22import javax.net.ssl.X509TrustManager;
23
24/**
25 * @author suren
26 * @date 2015年9月2日 上午10:52:31
27 */
28public class SSLTcpClient
29{
30
31	/**
32	 * @param args
33	 * @throws IOException 
34	 * @throws UnknownHostException 
35	 * @throws NoSuchAlgorithmException 
36	 * @throws KeyManagementException 
37	 * @throws KeyStoreException 
38	 * @throws CertificateException 
39	 * @throws UnrecoverableKeyException 
40	 */
41	public static void main(String[] args) throws UnknownHostException, IOException, NoSuchAlgorithmException, KeyManagementException, KeyStoreException, CertificateException, UnrecoverableKeyException
42	{
43		SSLContext context = SSLContext.getInstance("SSL");
44		context.init(null,
45				new TrustManager[]{new X509TrustManager(){
46
47					@Override
48					public void checkClientTrusted(X509Certificate[] chain,
49							String authType) throws CertificateException
50					{
51					}
52
53					@Override
54					public void checkServerTrusted(X509Certificate[] chain,
55							String authType) throws CertificateException
56					{
57					}
58
59					@Override
60					public X509Certificate[] getAcceptedIssuers()
61					{
62						return null;
63					}
64				}},
65				new SecureRandom());
66		
67		SSLSocketFactory factory = context.getSocketFactory();
68		
69		try(SSLSocket client = (SSLSocket) factory.createSocket("localhost", 8900))
70		{
71			InputStream input = client.getInputStream();
72			OutputStream output = client.getOutputStream();
73			
74			output.write("from ssl client.".getBytes());
75			
76			StringBuffer strBuf = new StringBuffer();
77			byte[] buf = new byte[1024];
78			int len = -1;
79			while((len = input.read(buf)) > 0)
80			{
81				strBuf.append(new String(buf, 0, len));
82				
83				if(len < buf.length)
84				{
85					break;
86				}
87			}
88			
89			System.out.println(strBuf);
90		}
91	}
92}

[/codesyntax]

• 参考

http://410063005.iteye.com/blog/1751243 http://www.ibm.com/developerworks/cn/java/j-lo-ssltls/