HTTP协议属于应用层协议，它构建于TCP和IP协议之上，处于TCP/IP协议架构层的顶端，所以，它不用处理下层协议间诸如丢包补发、握手及数据的分段及重新组装等繁琐的细节，使开发人员可以专注于应用业务。
协议是通信的规范，为了更好的理解HTTP协议，我们可以基于Java的Socket API接口，通过设计一个简单的应用层通信协议，来简单分析下协议实现的过程和细节。
在我们今天的示例程序中，客户端会向服务端发送一条命令，服务端在接收到命令后，会判断命令是否是“HELLO”，如果是“HELLO”， 则服务端返回给客户端的响应为“hello”，否则，服务端返回给客户端的响应为“bye bye”。
我们接下来用Java实现这个简单的应用层通信协议，说干就干，走起~~
协议请求的定义
协议的请求主要包括：编码、命令和命令长度三个字段。
package com.binghe.params; /** * 协议请求的定义 * @author binghe * */ public class Request { /** * 协议编码 */ private byte encode; /** * 命令 */ private String command; /** * 命令长度 */ private int commandLength; public Request() { super(); } public Request(byte encode, String command, int commandLength) { super(); this.encode = encode; this.command = command; this.commandLength = commandLength; } public byte getEncode() { return encode; } public void setEncode(byte encode) { this.encode = encode; } public String getCommand() { return command; } public void setCommand(String command) { this.command = command; } public int getCommandLength() { return commandLength; } public void setCommandLength(int commandLength) { this.commandLength = commandLength; } @Override public String toString() { return "Request [encode=" + encode + ", command=" + command + ", commandLength=" + commandLength + "]"; } }
响应协议的定义
协议的响应主要包括：编码、响应内容和响应长度三个字段。
package com.binghe.params; /** * 协议响应的定义 * @author binghe * */ public class Response { /** * 编码 */ private byte encode; /** * 响应内容 */ private String response; /** * 响应长度 */ private int responseLength; public Response() { super(); } public Response(byte encode, String response, int responseLength) { super(); this.encode = encode; this.response = response; this.responseLength = responseLength; } public byte getEncode() { return encode; } public void setEncode(byte encode) { this.encode = encode; } public String getResponse() { return response; } public void setResponse(String response) { this.response = response; } public int getResponseLength() { return responseLength; } public void setResponseLength(int responseLength) { this.responseLength = responseLength; } @Override public String toString() { return "Response [encode=" + encode + ", response=" + response + ", responseLength=" + responseLength + "]"; } }
编码常量定义
编码常量的定义主要包括UTF-8和GBK两种编码。
package com.binghe.constant; /** * 常量类 * @author binghe * */ public final class Encode { //UTF-8编码 public static final byte UTF8 = 1; //GBK编码 public static final byte GBK = 2; }
客户端的实现
客户端先构造一个request请求，通过Socket接口将其发送到远端，并接收远端的响应信息，并构造成一个Response对象。
package com.binghe.protocol.client; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.net.Socket; import com.binghe.constant.Encode; import com.binghe.params.Request; import com.binghe.params.Response; import com.binghe.utils.ProtocolUtils; /** * 客户端代码 * @author binghe * */ public final class Client { public static void main(String[] args) throws IOException{ //请求 Request request = new Request(); request.setCommand("HELLO"); request.setCommandLength(request.getCommand().length()); request.setEncode(Encode.UTF8); Socket client = new Socket("127.0.0.1", 4567); OutputStream out = client.getOutputStream(); //发送请求 ProtocolUtils.writeRequest(out, request); //读取响应数据 InputStream in = client.getInputStream(); Response response = ProtocolUtils.readResponse(in); System.out.println("获取的响应结果信息为: " + response.toString()); } }
服务端的实现
服务端接收客户端的请求，根据接收命令的不同，响应不同的消息信息，如果是“HELLO”命令，则响应“hello”信息，否则响应“bye bye”信息。
package com.binghe.protocol.server; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.net.ServerSocket; import java.net.Socket; import com.binghe.constant.Encode; import com.binghe.params.Request; import com.binghe.params.Response; import com.binghe.utils.ProtocolUtils; /** * Server端代码 * @author binghe * */ public final class Server { public static void main(String[] args) throws IOException{ ServerSocket server = new ServerSocket(4567); while (true) { Socket client = server.accept(); //读取请求数据 InputStream input = client.getInputStream(); Request request = ProtocolUtils.readRequest(input); System.out.println("收到的请求参数为: " + request.toString()); OutputStream out = client.getOutputStream(); //组装响应数据 Response response = new Response(); response.setEncode(Encode.UTF8); if("HELLO".equals(request.getCommand())){ response.setResponse("hello"); }else{ response.setResponse("bye bye"); } response.setResponseLength(response.getResponse().length()); ProtocolUtils.writeResponse(out, response); } } }
ProtocolUtils工具类的实现
ProtocolUtils的readRequest方法将从传递进来的输入流中读取请求的encode、command和commandLength三个参数，进行相应的编码转化，构造成Request对象返回。而writeResponse方法则是将response对象的字段根据对应的编码写入到响应的输出流中。
有一个细节需要重点注意：OutputStream中直接写入一个int类型，会截取其低8位，丢弃其高24位，所以，在传递和接收数据时，需要进行相应的转化操作。
package com.binghe.utils; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import com.binghe.constant.Encode; import com.binghe.params.Request; import com.binghe.params.Response; /** * 协议工具类 * @author binghe * */ public final class ProtocolUtils { /** * 从输入流中反序列化Request对象 * @param input * @return * @throws IOException */ public static Request readRequest(InputStream input) throws IOException{ //读取编码 byte[] encodeByte = new byte[1]; input.read(encodeByte); byte encode = encodeByte[0]; //读取命令长度 byte[] commandLengthBytes = new byte[4]; input.read(commandLengthBytes); int commandLength = ByteUtils.byte2Int(commandLengthBytes); //读取命令 byte[] commandBytes = new byte[commandLength]; input.read(commandBytes); String command = ""; if(Encode.UTF8 == encode){ command = new String(commandBytes, "UTF-8"); }else if(Encode.GBK == encode){ command = new String(commandBytes, "GBK"); } //组装请求返回 Request request = new Request(encode, command, commandLength); return request; } /** * 从输入流中反序列化Response对象 * @param input * @return * @throws IOException */ public static Response readResponse(InputStream input) throws IOException{ //读取编码 byte[] encodeByte = new byte[1]; input.read(encodeByte); byte encode = encodeByte[0]; //读取响应长度 byte[] responseLengthBytes = new byte[4]; input.read(responseLengthBytes); int responseLength = ByteUtils.byte2Int(responseLengthBytes); //读取命令 byte[] responseBytes = new byte[responseLength]; input.read(responseBytes); String response = ""; if(Encode.UTF8 == encode){ response = new String(responseBytes, "UTF-8"); }else if(Encode.GBK == encode){ response = new String(responseBytes, "GBK"); } //组装请求返回 Response resp = new Response(encode, response, responseLength); return resp; } /** * 序列化请求信息 * @param output * @param response */ public static void writeRequest(OutputStream output, Request request) throws IOException{ //将response响应返回给客户端 output.write(request.getEncode()); //output.write(response.getResponseLength());直接write一个int类型会截取低8位传输丢弃高24位 output.write(ByteUtils.int2ByteArray(request.getCommandLength())); if(Encode.UTF8 == request.getEncode()){ output.write(request.getCommand().getBytes("UTF-8")); }else if(Encode.GBK == request.getEncode()){ output.write(request.getCommand().getBytes("GBK")); } output.flush(); } /** * 序列化响应信息 * @param output * @param response */ public static void writeResponse(OutputStream output, Response response) throws IOException{ //将response响应返回给客户端 output.write(response.getEncode()); //output.write(response.getResponseLength());直接write一个int类型会截取低8位传输丢弃高24位 output.write(ByteUtils.int2ByteArray(response.getResponseLength())); if(Encode.UTF8 == response.getEncode()){ output.write(response.getResponse().getBytes("UTF-8")); }else if(Encode.GBK == response.getEncode()){ output.write(response.getResponse().getBytes("GBK")); } output.flush(); } }
ByteUtils类的实现
package com.binghe.utils; /** * 字节转化工具类 * @author binghe * */ public final class ByteUtils { /** * 将byte数组转化为int数字 * @param bytes * @return */ public static int byte2Int(byte[] bytes){ int num = bytes[3] & 0xFF; num |= ((bytes[2] << 8) & 0xFF00); num |= ((bytes[1] << 16) & 0xFF0000); num |= ((bytes[0] << 24) & 0xFF000000); return num; } /** * 将int类型数字转化为byte数组 * @param num * @return */ public static byte[] int2ByteArray(int i){ byte[] result = new byte[4]; result[0] = (byte)(( i >> 24 ) & 0xFF); result[1] = (byte)(( i >> 16 ) & 0xFF); result[2] = (byte)(( i >> 8 ) & 0xFF); result[3] = (byte)(i & 0xFF); return result; } }
至此，我们这个应用层通信协议示例代码开发完成，怎么样，小伙伴们，是不是很简单呢？赶紧打开你的环境，手撸个Http协议吧！！
