手动模拟一个很简单的web server服务器实现_websocketserver模拟器

新建一个普通的Java Project项目

创建三个普通类

类的作用

• HttpServer ：使用 java.net.ServerSocket 监听客户端的请求，与客户端（浏览器）建立连接，获取 java.net.Socket对象以及java.io.InputStream 输入流对象和 java.io.OutputStream 输出流对象。
• Request 将客户端请求的数据封装成一个request对象。
• Response将服务器端响应的数据封装成一个Response对象。

代码

HttpServer的核心代码

• 创建一个SeverSokcet对象监听到指定端口上

int port = 8080;
    try {
      serverSocket =  new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));
    }
    catch (IOException e) {
      e.printStackTrace();
      System.exit(1);
    }
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• 使用serverSocket监听客户端（浏览器）的连接请求，监听到连接后生成Socket对象

Socket socket = null;
      InputStream input = null;
      OutputStream output = null;
      try {
        socket = serverSocket.accept();
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• 根据连接的Socket对象获取输入input/输出output流对象，将输入流InputStream对象传递给Request对象，将输入流OutputStream对象传递给Response对象。

 try {
        socket = serverSocket.accept();
        input = socket.getInputStream();
        output = socket.getOutputStream();

        // create Request object and parse
        Request request = new Request(input);
        request.parse();

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

        // Close the socket
        socket.close();

        //check if the previous URI is a shutdown command
        shutdown = request.getUri().equals(SHUTDOWN_COMMAND);
      }
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HttpServer的完整代码

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 =
    System.getProperty("user.dir") + File.separator  + "webroot";

  // shutdown command
  private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";

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

  public static void main(String[] args) {
    HttpServer server = new HttpServer();
    server.await();
  }

  public void await() {
    ServerSocket serverSocket = null;
    int port = 8080;
    try {
      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 {
        socket = serverSocket.accept();
        input = socket.getInputStream();
        output = socket.getOutputStream();

        // create Request object and parse
        Request request = new Request(input);
        request.parse();

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

        // 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();
        continue;
      }
    }
  }
}

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Request的核心代码：将输入流中的数据读取/解析出来

  public void parse() {
    // Read a set of characters from the socket
    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());
  }
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举例：在浏览器中输入：http://localhost:8080/test.html，上面的代码System.out.print(request.toString());就会打印出来如下请求信息：

GET /test.html HTTP/1.1
Host: localhost:8080
Connection: keep-alive
Cache-Control: max-age=0
sec-ch-ua: "Chromium";v="92", " Not A;Brand";v="99", "Google Chrome";v="92"
sec-ch-ua-mobile: ?0
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.107 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Sec-Fetch-Site: none
Sec-Fetch-Mode: navigate
Sec-Fetch-User: ?1
Sec-Fetch-Dest: document
Accept-Encoding: gzip, deflate, br
Accept-Language: zh-CN,zh;q=0.9
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以上就是request解析出来的请求信息，可以看到包括请求的地址（资源文件）/test.html 、请求头信息等。

Request的完整代码

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 = input;
  }

  public void parse() {
    // Read a set of characters from the socket
    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());
  }

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

  public String getUri() {
    return uri;
  }

}
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Response核心代码：封装响应信息，如响应头信息（协议名称http,Content-Type:Text/html等）以及读取请求的文件/资源，如test.html文件，然后放到输出流OutputStream里面，最后在返回给请求的客户端。请求的文件/资源会提前放在服务器的指定目录下，这里是webroot目录

public void sendStaticResource() throws IOException {
		byte[] bytes = new byte[BUFFER_SIZE];
		FileInputStream fis = null;
		try {
			File file = new File(HttpServer.WEB_ROOT, request.getUri());
			if (file.exists()) {

//				String responseHeader = "HTTP/1.1 200 success\r\n" + "Content-Type: text/html\r\n" + "\r\n";
				String responseHeader = "HTTP/1.1 200 success\r\n" + "\r\n";
				output.write(responseHeader.getBytes());

				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);
				}
			} else {
				// file not found
				String errorMessage = "HTTP/1.1 404 File Not Found\r\n" + "Content-Type: text/html\r\n"
						+ "Content-Length: 26\r\n" + "\r\n" + "<h1>File Not Found555</h1>";
				output.write(errorMessage.getBytes());
			}
		} catch (Exception e) {
			// thrown if cannot instantiate a File object
			System.out.println(e.toString());
		} finally {
			if (fis != null)
				fis.close();
		}
	}
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Response完整代码

package ex01.pyrmont;

import java.io.OutputStream;
import java.io.IOException;
import java.io.FileInputStream;
import java.io.File;

/*
  HTTP Response = Status-Line
    *(( general-header | response-header | entity-header ) CRLF)
    CRLF
    [ message-body ]
    Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
*/

public class Response {

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

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

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

	public void sendStaticResource() throws IOException {
		byte[] bytes = new byte[BUFFER_SIZE];
		FileInputStream fis = null;
		try {
			File file = new File(HttpServer.WEB_ROOT, request.getUri());
			if (file.exists()) {

//				String responseHeader = "HTTP/1.1 200 success\r\n" + "Content-Type: text/html\r\n" + "\r\n";
				String responseHeader = "HTTP/1.1 200 success\r\n" + "\r\n";
				output.write(responseHeader.getBytes());

				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);
				}
			} else {
				// file not found
				String errorMessage = "HTTP/1.1 404 File Not Found\r\n" + "Content-Type: text/html\r\n"
						+ "Content-Length: 26\r\n" + "\r\n" + "<h1>File Not Found555</h1>";
				output.write(errorMessage.getBytes());
			}
		} catch (Exception e) {
			// thrown if cannot instantiate a File object
			System.out.println(e.toString());
		} finally {
			if (fis != null)
				fis.close();
		}
	}
}
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测试

随便找一个test.html文件放到工程（服务器）指定的目录里，根据上面的代码可知，指定的目录为webroot.

注：这里的test.html文件就相当于是服务器的一个资源，远程的客户端可以请求该资源。

启动HttpServer类，运行main方法

浏览器中输入请求地址http://localhost:8080/test.html

结果

截图显示浏览器获取的了服务器端的资源文件test.html，完成了模拟一个简单的web server。

参考 ： 《how tomcat works》