HTTP协议的主要特点可概括如下&＃xff1a;

1.支持客户/服务器模式。
2.简单快速&＃xff1a;客户向服务器请求服务时&＃xff0c;只需传送请求方法和路径。请求方法常用的有GET、HEAD、POST。每种方法规定了客户与服务器联系的类型不同。由于HTTP协议简单&＃xff0c;使得HTTP服务器的程序规模小&＃xff0c;因而通信速度很快。
3.灵活&＃xff1a;HTTP允许传输任意类型的数据对象。正在传输的类型由Content-Type加以标记。
4.无连接&＃xff1a;无连接的含义是限制每次连接只处理一个请求。服务器处理完客户的请求&＃xff0c;并收到客户的应答后&＃xff0c;即断开连接。采用这种方式可以节省传输时间。
5.无状态&＃xff1a;HTTP协议是无状态协议。无状态是指协议对于事务处理没有记忆能力。缺少状态意味着如果后续处理需要前面的信息&＃xff0c;则它必须重传&＃xff0c;这样可能导致每次连接传送的数据量增大。另一方面&＃xff0c;在服务器不需要先前信息时它的应答就较快。

请求方法&＃xff08;所有方法全为大写&＃xff09;有多种&＃xff0c;各个方法的解释如下&＃xff1a;
GET     请求获取Request-URI所标识的资源
POST    在Request-URI所标识的资源后附加新的数据
HEAD    请求获取由Request-URI所标识的资源的响应消息报头
PUT     请求服务器存储一个资源&＃xff0c;并用Request-URI作为其标识
DELETE  请求服务器删除Request-URI所标识的资源
TRACE   请求服务器回送收到的请求信息&＃xff0c;主要用于测试或诊断
CONNECT 保留将来使用
OPTIONS 请求查询服务器的性能&＃xff0c;或者查询与资源相关的选项和需求

HTTP Request

由3部分组成:

• Method URI (Uniform resource identifier) protocol/version
• Request headers
• Entity body

Http Request 例子&＃xff1a;

POST /examples/default.jsp HTTP/1.1 //请求方法 统一资源定位符 协议/版本Accept: text/plain; text/html
Accept-Language: en-gb
Connection: Keep-Alive
Host: localhost
User-Agent: Mozilla/4.0 (compatible; MSIE 4.01; Windows 98)
Content-Length: 33
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip, deflate // 头lastName&＃61;Franks&firstName&＃61;Michael //实体

HTTP Responses 
也是由3部分组成&＃xff1a;

• 协议版本 状态 描述
• 响应头
• 实体

响应的例子: 

HTTP/1.1 200 OK
Server: Microsoft-IIS/4.0
Date: Mon, 5 Jan 2004 13:13:33 GMT
Content-Type: text/html
Last-Modified: Mon, 5 Jan 2004 13:13:12 GMT
Content-Length: 112




Welcome to Brainy Software



The Socket Class

Socket 是网络连接的终端&＃xff0c;它可以用来实现程序对网络资源的读写。创建一个Socket

public Socket(java.lang.String host, int port)

例如连接到yahoo&＃xff0c; new Socket("yahoo",80);

如下代码创建了一个套接字&＃xff0c;来与本地的HTTP服务器进行通信&＃xff0c;并接受服务器的响应。 

Socket socket &＃61; new Socket("127.0.0.1", "8080"); OutputStream os &＃61; socket.getOutputStream(); boolean autoflush &＃61; true; PrintWriter out &＃61; new PrintWriter( socket.getOutputStream(), autoflush); BufferedReader in &＃61; new BufferedReader( new InputStreamReader( socket.getInputstream() )); // send an HTTP request to the web server out.println("GET /index.jsp HTTP/1.1"); out.println("Host: localhost:8080"); out.println("Connection: Close"); out.println(); // read the response boolean loop &＃61; true; StringBuffer sb &＃61; new StringBuffer(8096); while (loop) { if ( in.ready() ) { int i&＃61;0; while (i!&＃61;-1) { i &＃61; in.read(); sb.append((char) i); } loop &＃61; false; } Thread.currentThread().sleep(50); } // display the response to the out console System.out.println(sb.toString()); socket.close(); The ServerSocket class

new ServerSocket(8080, 1, InetAddress.getByName("127.0.0.1"));

The Application

我们的服务器端程序由3部分组成&＃xff1a;

• HttpServer  
• Request  
• Response  

The HttpServer class

Listing 1.1: The HttpServer class package ex01.pyrmont; import java.net.Socket;
import java.net.ServerSocket;
import java.net.InetAddress;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.IOException;
import java.io.File; public class HttpServer { /** WEB_ROOT is the directory where our HTML and other files reside. * For this package, WEB_ROOT is the "webroot" directory under the * working directory. * The working directory is the location in the file system * from where the java command was invoked. */ public static final String WEB_ROOT &＃61; System.getProperty("user.dir") &＃43; File.separator &＃43; "webroot"; // shutdown command private static final String SHUTDOWN_COMMAND &＃61; "/SHUTDOWN"; // the shutdown command received private boolean shutdown &＃61; false; public static void main(String[] args) { HttpServer server &＃61; new HttpServer(); server.await(); } public void await() { ... }
}

Listing 1.2: The HttpServer class&＃39;s await method public void await() { ServerSocket serverSocket &＃61; null; int port &＃61; 8080; try { serverSocket &＃61; new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1")); } catch (IOException e) { e.printStackTrace(); System.exit(1); } // Loop waiting for a request while (!shutdown) { Socket socket &＃61; null; InputStream input &＃61; null; OutputStream output &＃61; null; try { socket &＃61; serverSocket.accept(); input &＃61; socket.getInputStream(); output &＃61; socket.getOutputStream(); // create Request object and parse Request request &＃61; new Request(input); request.parse(); // create Response object Response response &＃61; new Response(output); response.setRequest(request); response.sendStaticResource(); // Close the socket socket.close(); //check if the previous URI is a shutdown command shutdown &＃61; request.getUri().equals(SHUTDOWN_COMMAND); } catch (Exception e) { e.printStackTrace (); continue; } }
}

这个web服务器可以提供静态资源服务。 
public static final WEB_ROOT and all subdirectories under it. WEB_ROOT is 
initialized as follows: 
public static final String WEB_ROOT &＃61;   System.getProperty("user.dir") &＃43; File.separator &＃43; "webroot"; 
这行代码列出webroot的目录&＃xff0c;包含许多静态资源&＃xff0c;如果想请求一个静态资源&＃xff0c;你在浏览器中可以输入 
http://machineName:port/staticResource 例如&＃xff1a;http://localhost:8080/index.html 

The Request Class

Listing 1.3: The Request class package ex01.pyrmont; import java.io.InputStream;
import java.io.IOException; public class Request { private InputStream input; private String uri; public Request(InputStream input) { this.input &＃61; input; } public void parse() { ... } private String parseUri(String requestString) { ... } public String getUri() { return uri; }
}

Listing 1.4: The Request class&＃39;s parse method public void parse() { // Read a set of characters from the socket StringBuffer request &＃61; new StringBuffer(2048); int i; byte[] buffer &＃61; new byte[2048]; try { i &＃61; input.read(buffer); } catch (IOException e) { e.printStackTrace(); i &＃61; -1; } for (int j&＃61;0; j}

Listing 1.5: the Request class&＃39;s parseUri method private String parseUri(String requestString) { int index1, index2; index1 &＃61; requestString.indexOf(&＃39; &＃39;); if (index1 !&＃61; -1) { index2 &＃61; requestString.indexOf(&＃39; &＃39;, index1 &＃43; 1); if (index2 > index1) return requestString.substring(index1 &＃43; 1, index2); } return null;
}

The Response class

Listing 1.6: The Response class package ex01.pyrmont; import java.io.OutputStream;
import java.io.IOException;
import java.io.FileInputStream;
import java.io.File; /* HTTP Response &＃61; Status-Line *(( general-header | response-header | entity-header ) CRLF) CRLF [ message-body ] Status-Line &＃61; HTTP-Version SP Status-Code SP Reason-Phrase CRLF
*/ public class Response { private static final int BUFFER_SIZE &＃61; 1024; Request request; OutputStream output; public Response(OutputStream output) { this.output &＃61; output; } public void setRequest(Request request) { this.request &＃61; request; } public void sendStaticResource() throws IOException { byte[] bytes &＃61; new byte[BUFFER_SIZE]; FileInputStream fis &＃61; null; try { File file &＃61; new File(HttpServer.WEB_ROOT, request.getUri()); if (file.exists()) { fis &＃61; new FileInputStream(file); int ch &＃61; fis.read(bytes, 0, BUFFER_SIZE); while (ch!&＃61;-1) { output.write(bytes, 0, ch); ch &＃61; fis.read(bytes, 0, BUFFER_SIZE); } } else { // file not found String errorMessage &＃61; "HTTP/1.1 404 File Not Found\r\n" &＃43; "Content-Type: text/html\r\n" &＃43; "Content-Length: 23\r\n" &＃43; "\r\n" &＃43; "

File Not Found

Run the application

在浏览器中输入http://localhost:8080/index.html  

在控制台&＃xff0c;你会看到&＃xff1a;

GET /index.html HTTP/1.1 
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, 
application/vnd.ms-excel, application/msword, application/vnd.ms- 
powerpoint, application/x-shockwave-flash, application/pdf, */* 
Accept-Language: en-us 
Accept-Encoding: gzip, deflate 
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; .NET CLR 
1.1.4322) 
Host: localhost:8080 
Connection: Keep-Alive 
 
GET /images/logo.gif HTTP/1.1 
Accept: */* 
Referer: http://localhost:8080/index.html 
Accept-Language: en-us 
Accept-Encoding: gzip, deflate 
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; .NET CLR 
1.1.4322) 
Host: localhost:8080 
Connection: Keep-Alive