tomcat4源码剖析（二）——简单的Servlet容器

最新推荐文章于 2022-05-24 11:42:34 发布

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本文介绍了一个简单的Servlet容器的构建过程，涵盖了容器的基本功能，如URL解析、请求处理、静态资源与Servlet的区分加载，以及核心类如HttpServer1、Request、Response等的实现细节。

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好久没有写博客了，最近要毕业了，写论文写的好烦。然后就又拿起了这本《深入剖析tomcat》来看一看。哎，希望今年能顺利毕业。

其实本篇也就是对《深入理解tomcat》中第二章第一个简单的servlet容器的代码进行分析。

一、简单Servlet容器的功能

本篇所构建的Servlet功能如下：
1，解析请求的url，将url封装成一个自定义的Request。解析包括对请求服务器资源名称的解析。
2，接收浏览器的请求，根据请求的URL的类型。选择是加载一个Servlet类还是返回系统的静态文件。当URL中包含/servlet/关键路径时，加载指定的Servlet，当不包含时，加载静态文件。
3，若加载的是Servlet调用该Servlet的service()方法，当是静态文件的时候，直接返回文件。在传输完成后，关闭socket

二、系统类简介

HttpServer1：程序启动的总入口
Request ：在接收到浏览器请求时，HttpServer1利用Request将请求进行包装
Response：对浏览器的回应封装
StaticResourceProcessor：处理静态资源的类
ServletProcessor1：处理请求是Servlet时的类
Constants：系统常量

三、代码结构

在src目录下，建立ex02.pyrmont包。同时在src同级目录下建立webroot目录，里面包含一个index.html静态资源以及一个编译好的Servlet。

三、源码解析

1,HttpServer1.java

package ex02.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;

public class HttpServer1 {
  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;
    int port = 8080;
    try {
      serverSocket =  new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));
    }
    catch (IOException e) {
      e.printStackTrace();
      System.exit(1);
    }

    while (!shutdown) {
      Socket socket = null;
      InputStream input = null;
      OutputStream output = null;
      try {
        socket = serverSocket.accept();
        input = socket.getInputStream();
        output = socket.getOutputStream();

        // 将浏览器的请求封装成一个自定义的Request
        Request request = new Request(input);
        request.parse();

        // 建立一个相应类
        Response response = new Response(output);
        response.setRequest(request);

        // 通过上面Request解析后的URl判断该URI中是否包含“/servlet/”路径，如果有，调用ServletProcessor1类相应
        //浏览器，如果没有，调用StaticResourceProcessor相应浏览器
        if (request.getUri().startsWith("/servlet/")) {
          ServletProcessor1 processor = new ServletProcessor1();
          processor.process(request, response);
        }
        else {
          StaticResourceProcessor processor = new StaticResourceProcessor();
          processor.process(request, response);
        }

        // 在回复浏览器后，关闭与浏览器产生联系的套接字
        socket.close();
        //判断一下浏览器指令是否为关闭服务器
        shutdown = request.getUri().equals(SHUTDOWN_COMMAND);
      }
      catch (Exception e) {
        e.printStackTrace();
        System.exit(1);
      }
    }
  }
}

在HttpServer1中启动后，主要是调用await()方法，在该方法中建立一个serverSocket。用来监控本地的8080端口，在接收到浏览器的请求后，创建Request对象将浏览器请求封装。然后通过请求的URL判断是请求的静态文件还是Servlet。最后关闭socket。

2,Request.java 源码如下

package ex02.pyrmont;

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.*;


public class Request implements ServletRequest {

  private InputStream input;
  private String uri;

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

  public String getUri() {
    return uri;
  }

  // 解析传递过来的URI，形如： GET /servlet/PrimitiveServlet HTTP/1.1
  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;
  }

// 从建立的socket中获取浏览器传送过来的信息，其实就是tomcat4源码剖析（一）中讲到的一般请求过程
  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]);
    }
    // request中就是浏览器传递过来的东西
    System.out.print(request.toString());
    uri = parseUri(request.toString()); // 解析浏览器传递过来的URI
  }

   //之后添加的是继承ServletRequest需要实现的方法，暂时不需要管
  /* implementation of the ServletRequest*/
  public Object getAttribute(String attribute) {
    return null;
  }

  public Enumeration getAttributeNames() {
    return null;
  }

  public String getRealPath(String path) {
    return null;
  }

  public RequestDispatcher getRequestDispatcher(String path) {
    return null;
  }

  public boolean isSecure() {
    return false;
  }

  public String getCharacterEncoding() {
    return null;
  }

  public int getContentLength() {
    return 0;
  }

  public String getContentType() {
    return null;
  }

  public ServletInputStream getInputStream() throws IOException {
    return null;
  }

  public Locale getLocale() {
    return null;
  }

  public Enumeration getLocales() {
    return null;
  }

  public String getParameter(String name) {
    return null;
  }

  public Map getParameterMap() {
    return null;
  }

  public Enumeration getParameterNames() {
    return null;
  }

  public String[] getParameterValues(String parameter) {
    return null;
  }

  public String getProtocol() {
    return null;
  }

  public BufferedReader getReader() throws IOException {
    return null;
  }

  public String getRemoteAddr() {
    return null;
  }

  public String getRemoteHost() {
    return null;
  }

  public String getScheme() {
   return null;
  }

  public String getServerName() {
    return null;
  }

  public int getServerPort() {
    return 0;
  }

  public void removeAttribute(String attribute) {
  }

  public void setAttribute(String key, Object value) {
  }

  public void setCharacterEncoding(String encoding)
    throws UnsupportedEncodingException {
  }

  @Override
  public long getContentLengthLong() {
    return 0;
  }

  @Override
  public int getRemotePort() {
    return 0;
  }

  @Override
  public String getLocalName() {
    return null;
  }

  @Override
  public String getLocalAddr() {
    return null;
  }

  @Override
  public int getLocalPort() {
    return 0;
  }

  @Override
  public ServletContext getServletContext() {
    return null;
  }

  @Override
  public AsyncContext startAsync() throws IllegalStateException {
    return null;
  }

  @Override
  public AsyncContext startAsync(ServletRequest servletRequest, ServletResponse servletResponse) throws IllegalStateException {
    return null;
  }

  @Override
  public boolean isAsyncStarted() {
    return false;
  }

  @Override
  public boolean isAsyncSupported() {
    return false;
  }

  @Override
  public AsyncContext getAsyncContext() {
    return null;
  }

  @Override
  public DispatcherType getDispatcherType() {
    return null;
  }
}

在Request类中，主要就做了一件事将如下字符串进行解析，并将其中的URI赋值给Request类中的uri变量。

GET /servlet/PrimitiveServlet HTTP/1.1
Host: localhost:8080
Connection: keep-alive
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.121 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
Accept-Encoding: gzip, deflate, br
Accept-Language: zh-CN,zh;q=0.9,en;q=0.8

3, Response.java

package ex02.pyrmont;

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 {
      /* request.getUri has been replaced by request.getRequestURI */
      File file = new File(Constants.WEB_ROOT, request.getUri());
      fis = new FileInputStream(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
      */
      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();
    }
  }


  /** implementation of ServletResponse  */
  public void flushBuffer() throws IOException {
  }

  public int getBufferSize() {
    return 0;
  }

  public String getCharacterEncoding() {
    return null;
  }

  public Locale getLocale() {
    return null;
  }

  public ServletOutputStream getOutputStream() throws IOException {
    return null;
  }

  public PrintWriter getWriter() throws IOException {
    // autoflush is true, println() will flush,
    // but print() will not.
    writer = new PrintWriter(output, true);
    return writer;
  }

  public boolean isCommitted() {
    return false;
  }

  public void reset() {
  }

  public void resetBuffer() {
  }

  public void setBufferSize(int size) {
  }

  public void setContentLength(int length) {
  }

  public void setContentType(String type) {
  }

  public void setLocale(Locale locale) {
  }

    public String getContentType() {
        return null;
    }

    public void setCharacterEncoding(String s) {

    }

    public void setContentLengthLong(long l) {

    }
}

Response类中最主要的就是sendStaticResource()方法，主要是在根据浏览器请求的是静态文件时，供StaticResourceProcessor类调用。在查找静态资源时，如果没有找到，则返回404页面。
4，ServletProcessor1.java

package ex02.pyrmont;

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) {

    String uri = request.getUri();
    String servletName = uri.substring(uri.lastIndexOf("/") + 1); //找到具体所要请求的servlet名字
    URLClassLoader loader = null; //类加载器

    try {
      // 创建类加载器
      URL[] urls = new URL[1];
      URLStreamHandler streamHandler = null;
      File classPath = new File(Constants.WEB_ROOT);
      String repository = (new URL("file", null, classPath.getCanonicalPath() + File.separator)).toString() ;
      urls[0] = new URL(null, repository, streamHandler);
      loader = new URLClassLoader(urls);
    }
    catch (IOException e) {
      System.out.println(e.toString() );
    }
    Class myClass = null;
    try {
      //加载相应的servlet.class文件
      myClass = loader.loadClass(servletName);
    }
    catch (ClassNotFoundException e) {
      System.out.println(e.toString());
    }

    Servlet servlet = null;

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

  }
}

ServletProcessor1的主要作用是根据指定的servlet名称找到对应的资源利用反射创建对应的servlet实例。然后调用实例的service()方法。
5，StaticResourceProcessor.java

package ex02.pyrmont;

import java.io.IOException;

public class StaticResourceProcessor {

  public void process(Request request, Response response) {
    try {
      response.sendStaticResource();// 调用response的静态方法
    }
    catch (IOException e) {
      e.printStackTrace();
    }
  }
}

6，Constants.java

package ex02.pyrmont;

import java.io.File;

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

WEB_ROOT 在本机上就是D:\F\IDEA程序\Tomcat\webroot路径。

6，PrimitiveServlet.java

import javax.servlet.*;
import java.io.IOException;
import java.io.PrintWriter;

public class PrimitiveServlet implements Servlet {
    @Override
    public void init(ServletConfig servletConfig) throws ServletException {

    }

    @Override
    public ServletConfig getServletConfig() {
        return null;
    }

    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        PrintWriter out = servletResponse.getWriter();
        out.println("HTTP/1.1 200 OK"); // 记住一定要加上这一句哦
        out.println("Server: zkw");
        out.println();
        out.println("<html>");
        out.println("Learning how tomcat works");
        out.println("</html>");
    }

    @Override
    public String getServletInfo() {
        return null;
    }

    @Override
    public void destroy() {

    }
}

7，index.html

HTTP/1.1 200 OK
Date: Fri, 22 May 2009 06:07:21 GMT
Content-Type: text/html; charset=UTF-8

<html>
<head>
<title>Welcome to BrainySoftware</title>
</head>
<body>
<br>
Welcome to BrainySoftware.
</body>
</html>

注意要加上前面的三行。

四、其他

1，运行
在浏览器输入
http://localhost:8080/servlet/PrimitiveServlet 之后，出现如下图片
在这里插入图片描述
在浏览器输入http://localhost:8080/index.html 后出现如下图片

2 建议
第三节中代码为完整代码，可以直接复制到自己工程项目中运行。同时也上传了项目的完整代码，下载地址：https://download.youkuaiyun.com/download/tyoukai_/11019831