用java开发一个简单的web服务器

本文会初步介绍web应用中的服务器，客户端模型，帮助新人大致了解一个网络中处理请求的框架，最后用java实现了一个简单服务器(处理静。

首先指出客户端与用户端的实质，它们都是进程。(一台主机自然可以运行多个不同的客户端与服务器)

下图是客户端与服务器交互的一个基本模型

发送请求

客户端--------------------------> 服务器<--------------------------------------->资源

<------------------------      调用资源处理请求

响应请求

我们用一个例子来说明这个模型

若我们在网站中输入一个网址(也就是一个请求)如www.google.com:80/index.html,分为三个部分。

1.www.google.com 服务器所在的主机

2.:80   80指端口号：用于与前面隔开,计算机中一个端口对应一个进程，这也再次说明服务器就是一个进程。

3./index.html 主机中的资源文件，每条由服务器返回的内容都与其管理的某个文件相关联。

有了这些基本了解我们就着手实现一个服务器。

首先创建一个服务器入口

import java.net.Socket;
import java.net.ServerSocket;
import java.net.InetAddress;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.IOException;

public class HttpServer1 {

//服务器入口处
// shutdown command
private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";

// the shutdown command received
private boolean shutdown = false;

public static void main(String[] args) {

HttpServer1 server = new HttpServer1();
server.await();
}

public void await() {
ServerSocket serverSocket = null; //由于我们的服务器端要一直等待,所以用了ServerSocket这个类一直等待直到接收消息
int port = 8080;
try {
//设置端口号及服务器主机地址
serverSocket = 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 = null;
InputStream input = null;
OutputStream output = null;
try {
//一个服务器必须要有一个接收流对象与一个输出流对象
socket = serverSocket.accept();
input = socket.getInputStream();
output = socket.getOutputStream();

// create Request object and parse
Request request = new Request(input);
//解析浏览器中输入的网址
request.parse();

// create Response object
Response response = new Response(output);
response.setRequest(request);

//检查是否以"/servlet/"开头(也可以以其它字母开头再对应去处理，这便是动态处理)，否则处理静态资源
if (request.getUri().startsWith("/servlet/")) {
ServletProcessor1 processor = new ServletProcessor1();
processor.process(request, response);

}
else {
StaticResourceProcessor processor = new StaticResourceProcessor();
processor.process(request, response);
}

// Close the socket
socket.close();
//check if the previous URI is a shutdown command
shutdown = request.getUri().equals(SHUTDOWN_COMMAND);
}
catch (Exception e) {
e.printStackTrace();
System.exit(1);
}
}
}
}

Constants用来存储我们的文件目录

import java.io.File;

public class Constants {
public static final String WEB_ROOT =
System.getProperty("user.dir") + File.separator  + "webroot";
}

Request，服务器请求类的实现,还有许多接口方法没有列举出来，因为此处仅是实现一个最基本的Request故暂不实现它们。

import java.io.InputStream;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.UnsupportedEncodingException;
import java.util.Enumeration;
import java.util.Locale;
import java.util.Map;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletRequest;

public class Request implements ServletRequest {

private InputStream input;
private String uri;

public Request(InputStream input) {
this.input = input;
}

public String getUri() {
return uri;
}

private String parseUri(String requestString) {
int index1, index2;

4000
index1 = requestString.indexOf(' ');
if (index1 != -1) {
index2 = requestString.indexOf(' ', index1 + 1);
if (index2 > index1)
return requestString.substring(index1 + 1, index2);
}
return null;
}

public void parse() {
// 读取请求的信息
StringBuffer request = new StringBuffer(2048);
int i;
byte[] buffer = new byte[2048];
try {
i = input.read(buffer);
}
catch (IOException e) {
e.printStackTrace();
i = -1;
}
for (int j=0; j<i; j++) {
request.append((char) buffer[j]);
}
System.out.print(request.toString());
uri = parseUri(request.toString());
}

}

同样Response类.
import java.io.OutputStream;
import java.io.IOException;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.File;
import java.io.PrintWriter;
import java.util.Locale;

import javax.servlet.ServletResponse;
import javax.servlet.ServletOutputStream;

public class Response implements ServletResponse {

private static final int BUFFER_SIZE = 1024;
Request request;
OutputStream output;
PrintWriter writer;

public Response(OutputStream output) {
this.output = output;
}

public void setRequest(Request request) {
this.request = request;
}

/* This method is used to serve a static page */
public void sendStaticResource() throws IOException {
byte[] bytes = new byte[BUFFER_SIZE];
FileInputStream fis = null;
try {
//根据我们Constant中指定目录与浏览器解析的地址去初始化一个文件。
File file = new File(Constants.WEB_ROOT, request.getUri());
fis = new FileInputStream(file);
int ch = fis.read(bytes, 0, BUFFER_SIZE);
while (ch!=-1) {
output.write(bytes, 0, ch);
ch = fis.read(bytes, 0, BUFFER_SIZE);
}
}
catch (FileNotFoundException e) {
String errorMessage = "HTTP/1.1 404 File Not Found\r\n" +
"Content-Type: text/html\r\n" +
"Content-Length: 23\r\n" +
"\r\n" +
"<h1>File Not Found</h1>";
output.write(errorMessage.getBytes());
}
finally {
if (fis!=null)
fis.close();
}
}
动态处理类
import java.net.URL;

import java.net.URLClassLoader;
import java.net.URLStreamHandler;
import java.io.File;
import java.io.IOException;
import javax.servlet.Servlet;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class ServletProcessor1 {

public void process(Request request, Response response) {
// TODO Auto-generated method stub

String uri = request.getUri();
String servletName = uri.substring(uri.lastIndexOf("/") + 1);
URLClassLoader loader = null;

try {
// create a URLClassLoader
URL[] urls = new URL[1];
URLStreamHandler streamHandler = null;
File classPath = new File(Constants.WEB_ROOT);
// the forming of repository is taken from the createClassLoader method in
// org.apache.catalina.startup.ClassLoaderFactory

String repository = (new URL("file", null, classPath.getCanonicalPath() + File.separator)).toString() ;
System.out.println("repository="+repository);
// the code for forming the URL is taken from the addRepository method in
// org.apache.catalina.loader.StandardClassLoader class.
urls[0] = new URL(null, repository, streamHandler);
System.out.println("urls="+urls[0].toString());
// System.out.print(urls[0].toString());
loader = new URLClassLoader(urls);
}
catch (IOException e) {
System.out.println(e.toString() );
}
Class myClass = null;
try {
myClass = loader.loadClass(servletName);
}
catch (ClassNotFoundException e) {
System.out.println(e.toString());
}

Servlet servlet = null;

try {
servlet = (Servlet) myClass.newInstance();
servlet.service((ServletRequest) request, (ServletResponse) response);
}
catch (Exception e) {
System.out.println(e.toString());
}
catch (Throwable e) {
System.out.println(e.toString());
}

}
}

静态处理类
import java.io.IOException;

public class StaticResourceProcessor {

public void process(Request request, Response response) {
// TODO Auto-generated method stub
try {
response.sendStaticResource();
}
catch (IOException e) {
e.printStackTrace();
}
}
}