《how tomcat work》 搬运工 charpter2: A Simple Servlet Container

这一章介绍了servlet container,application中对应的类是主要是httpServer1,这个类是创建socket绑定端口，接受请求，然后创建request实例和response实例，根据request的uri来处理请求，如果是静态资源就创建StaticResourceProcessor实例来处理，如果是servlet请求则创建对应servlet来处理请求

这章节的request和response类继承了servletRequest接口，所以对应的pom要添加依赖项

　　　　<dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-web-api</artifactId>
            <version>6.0</version>
            <scope>provided</scope>
        </dependency>

 

request类

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.AsyncContext;
import javax.servlet.DispatcherType;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

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;
        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() {
        // 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());
    }

    /* implementation of the ServletRequest */
}

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 {
          /* 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();
        }
      }

　　　

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

/** implementation of ServletResponse  */
}

static字段类

import java.io.File;

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

}

处理请求的类

1.StaticResourceProcessor

import java.io.IOException;

public class StaticResourceProcessor {
    public void process(Request request, Response response) {
        try {
          response.sendStaticResource();
        }
        catch (IOException e) {
          e.printStackTrace();
        }
      }
}

2.ServletProcessor1

      这个类有一处是根据servlet的名称来加载class文件，class文件PrimitiveServlet已经在webroot文件中了

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);
        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();
            // 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);
            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());
        }

    }
}

 

 

绑定端口的类，函数入口

HttpServer1   

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);
        }

        // 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);

            // check if this is a request for a servlet or a static resource
            // a request for a servlet begins with "/servlet/"
            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);
          }
        }
      }
}

运行application

在浏览器输入http://localhost:8080/servlet/PrimitiveServlet 则会创建PrimitiveServlet来处理请求

浏览器接收到Hello. Roses are red.的结果

ps:

PrimitiveServlet.java代码

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

public class PrimitiveServlet implements Servlet {

  public void init(ServletConfig config) throws ServletException {
    System.out.println("init");
  }

  public void service(ServletRequest request, ServletResponse response)
    throws ServletException, IOException {
    System.out.println("from service");
    PrintWriter out = response.getWriter();
    out.println("Hello. Roses are red.");
    out.print("Violets are blue.");
  }

  public void destroy() {
    System.out.println("destroy");
  }

  public String getServletInfo() {
    return null;
  }
  public ServletConfig getServletConfig() {
    return null;
  }

}

 

 

但是上面的application有一个严重的缺陷，就是response实例和request实例在传递给两个处理实例StaticResourceProcessor和ServletProcessor1时，进行了upcast,就是 

try {

servlet = (Servlet) myClass.newInstance();

servlet.service((ServletRequest) request, (ServletResponse) response);

}

所以在servlet实例中，当执行service(ServletRequest,ServletResponse)函数时，会将

已经upcast的request和response进行现式的downcast，如何调用一些除了ServletRequest,ServletResponse定义以外的函数，这些函数是没有设计成在service中调用的。

这样就会出现一些意料之外的错误。

解决方法有很多种，现在采用的是添加facade类

RequestFacade类

ps. 由于how tomcat work书的出版是比较旧的，所以用的 serclerRequest接口也是旧的，一些新定义的

函数需要实现，具体实现对比着其他函数的实现，以下代码是原书的代码

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 RequestFacade implements ServletRequest {

  private ServletRequest request = null;

  public RequestFacade(Request request) {
    this.request = request;
  }

  /* implementation of the ServletRequest*/
  public Object getAttribute(String attribute) {
    return request.getAttribute(attribute);
  }

  public Enumeration getAttributeNames() {
    return request.getAttributeNames();
  }

  public String getRealPath(String path) {
    return request.getRealPath(path);
  }

  public RequestDispatcher getRequestDispatcher(String path) {
    return request.getRequestDispatcher(path);
  }

  public boolean isSecure() {
    return request.isSecure();
  }

  public String getCharacterEncoding() {
    return request.getCharacterEncoding();
  }

  public int getContentLength() {
    return request.getContentLength();
  }

  public String getContentType() {
    return request.getContentType();
  }

  public ServletInputStream getInputStream() throws IOException {
    return request.getInputStream();
  }

  public Locale getLocale() {
    return request.getLocale();
  }

  public Enumeration getLocales() {
    return request.getLocales();
  }

  public String getParameter(String name) {
    return request.getParameter(name);
  }

  public Map getParameterMap() {
    return request.getParameterMap();
  }

  public Enumeration getParameterNames() {
    return request.getParameterNames();
  }

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

  public String getProtocol() {
    return request.getProtocol();
  }

  public BufferedReader getReader() throws IOException {
    return request.getReader();
  }

  public String getRemoteAddr() {
    return request.getRemoteAddr();
  }

  public String getRemoteHost() {
    return request.getRemoteHost();
  }

  public String getScheme() {
   return request.getScheme();
  }

  public String getServerName() {
    return request.getServerName();
  }

  public int getServerPort() {
    return request.getServerPort();
  }

  public void removeAttribute(String attribute) {
    request.removeAttribute(attribute);
  }

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

  public void setCharacterEncoding(String encoding)
    throws UnsupportedEncodingException {
    request.setCharacterEncoding(encoding);
  }

}

ResponseFacade类

ps.同上

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Locale;
import javax.servlet.ServletResponse;
import javax.servlet.ServletOutputStream;

public class ResponseFacade implements ServletResponse {

  private ServletResponse response;
  public ResponseFacade(Response response) {
    this.response = response;
  }

  public void flushBuffer() throws IOException {
    response.flushBuffer();
  }

  public int getBufferSize() {
    return response.getBufferSize();
  }

  public String getCharacterEncoding() {
    return response.getCharacterEncoding();
  }

  public Locale getLocale() {
    return response.getLocale();
  }

  public ServletOutputStream getOutputStream() throws IOException {
    return response.getOutputStream();
  }

  public PrintWriter getWriter() throws IOException {
    return response.getWriter();
  }

  public boolean isCommitted() {
    return response.isCommitted();
  }

  public void reset() {
    response.reset();
  }

  public void resetBuffer() {
    response.resetBuffer();
  }

  public void setBufferSize(int size) {
    response.setBufferSize(size);
  }

  public void setContentLength(int length) {
    response.setContentLength(length);
  }

  public void setContentType(String type) {
    response.setContentType(type);
  }

  public void setLocale(Locale locale) {
    response.setLocale(locale);
  }

}

ServletProcessor2类

这个和ServletProcessor1的区别就是用request和response来创建

RequestFacade requestFacade = new RequestFacade(request);
ResponseFacade responseFacade = new ResponseFacade(response);

实例来实现servlet对request和response的超权限调用

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 ServletProcessor2 {

  public void process(Request request, Response response) {

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

  }
}

HttpServer2

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 HttpServer2 {

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

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

  public static void main(String[] args) {
    HttpServer2 server = new HttpServer2();
    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);

        //check if this is a request for a servlet or a static resource
        //a request for a servlet begins with "/servlet/"
        if (request.getUri().startsWith("/servlet/")) {
          ServletProcessor2 processor = new ServletProcessor2();
          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);
      }
    }
  }
}

 完整目录结构