一個簡單的servlet容器

時間  2019-12-15
標籤 一個 簡單 servlet 容器 欄目 Tomcat 简体版
原文   原文鏈接

【0】READMEhtml

0.1）本文部分文字轉自　「深刻剖析Tomcat」，旨在學習  一個簡單的servlet容器  的基礎知識；java

0.2）for complete source code, please visit  https://github.com/pacosonTang/HowTomcatWorks/tree/master/chapter2git

0.3）文件目錄以下：程序員

 

 

【1】javax.servlet.Servlet接口github

1）intro Servlet：Servlet編程須要使用到 javax.servlet 和 javax.servlet.http 兩個包下的接口和類。在全部的類和接口中， javax.servlet.servlet 接口是最爲重要的。全部的servlet 程序都必須實現該接口或繼承自實現了該接口的類；
2）Servlet接口中聲明瞭5個方法： init， service， destroy， getServletConfig， getServletInfo 方法；
2.0）init， service， destroy方法是與 servlet的生命週期相關的方法；
2.1）init方法：當實例化某個servlet類後；servlet容器會調用其 init() 方法進行初始化，servlet只調用該方法一次；且servlet 程序員能夠覆蓋此方法，在其中編寫僅須要執行一次的初始化代碼；
2.2）service方法：當一個servlet客戶端請求到達後，servlet容器就調用相應的servlet的service方法，並將 servletRequest 和 servletResponse 對象做爲參數傳入；
2.3）destroy方法：當servlet容器關閉或servlet容器要釋放內存時，纔會將 servlet實例移除，並且只有當servlet實例的service方法中的全部線程都退出或執行超時後，纔會調用 destroy方法；
3）看個荔枝：
 
【2】應用程序1
1）一個功能齊全的 servlet容器有如下幾件事情要作（things）：
t1）當第一次調用某個 servlet 時，要載入該 servlet類，並調用其 init() 方法；（僅此一次）
t2）針對每一個request請求， 建立一個 javax.servlet.ServletRequest 實例 和 一個 javax.servlet.ServletResponse 實例；
t3）調用該 servlet 的 service() 方法，將 servletRequest對象和 servletResponse對象做爲參數傳入；
t4）當關閉該servlet類時，調用其 destroy() 方法，並卸載該servlet類；
2）servlet容器的實現源碼和訪問結果
2.1）printing results
2.2）source code at a glance 
package com.tomcat.chapter2;

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

// HttpServer1 類 既能夠對靜態資源請求，也能夠對servlet資源請求
public class HttpServer1 {

  /** 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.
   */
  // 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;
    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/")) { // 若HTTP請求的是servlet(以servlet打頭)
          ServletProcessor1 processor = new ServletProcessor1();
          processor.process(request, response);
        } // 若http請求的是靜態資源
        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);
      }
    }
  }
}
package com.tomcat.chapter2;

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;

// 用於處理對servlet 資源的HTTP 請求
public class ServletProcessor1 {

  public void process(Request request, Response response) {

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

    try {
      // create a URLClassLoader, 建立類載入器（類加載器是乾貨代碼 ）
      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() ;
      // file:E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\webroot\
      // 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);
      // urls[0] = file:E:/bench-cluster/cloud-data-preprocess/HowTomcatWorks/webroot/
      loader = new URLClassLoader(urls);
    }
    catch (IOException e) {
      System.out.println(e.toString() );
    }
    Class myClass = null;
    try {
      myClass = loader.loadClass("servlet."+servletName); // 載入 servlet類
    }
    catch (ClassNotFoundException e) {
      System.out.println(e.toString());
    }

    Servlet servlet = null;

    try {
      servlet = (Servlet) myClass.newInstance(); // 會建立已載入的servlet類的一個實例
      servlet.service((ServletRequest) request, (ServletResponse) response);
    }
    catch (Exception e) {
      System.out.println(e.toString());
    }
    catch (Throwable e) {
      System.out.println(e.toString());
    }

  }
}
package com.tomcat.chapter2;

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;
    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*/
  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 {
  }

}
package com.tomcat.chapter2;

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) {
  }
}
package com.tomcat.chapter2;

import java.io.IOException;

public class StaticResourceProcessor {

  public void process(Request request, Response response) {
    try {
      response.sendStaticResource();
    }
    catch (IOException e) {
      e.printStackTrace();
    }
  }
}
package com.tomcat.chapter2;

import java.io.File;

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

 

【3】應用程序2
1）problem：ServletProcessor1 中必須將Request 轉型爲 javax.servlet.ServletRequest，將Response 轉型爲 javax.servlet.ServletResponse 實例，將它們做爲參數傳遞給 service方法；
1.1）這是不安全的作法： 一旦咱們有了Request 實例後，咱們就能夠調用其parse方法，而有了Response實例後，咱們就能夠調用其 sendStaticResource方法。不能將parse() 和 sendStaticResource() 設置爲私有方法，由於它們會被其餘類調用，但這兩個方法在servlet中不該該是可用的；
2）solution：使用外觀類（Facade）來解決
2.1）構建外觀類 RequestFacade 和 ResponseFacade：分別實現 ServletRequest 和 ServletResponse ，而後在其構造函數中指定Request 和 Response對象（private私有訪問權限） ，外觀類中的實現方法均調用 Request 或 Response對象的相應方法；
3）Conclusion：引入外觀類的目的是， 不向外界提供訪問到Request 和 Response 的接口；
4）源代碼實現和打印結果
4.1）打印結果同 HttpServer1，故 omit it；
4.2）源代碼實現（我這裏給給出外觀類代碼，其餘和HttpServer1 中的相似） 
package com.tomcat.chapter2;

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);
      }
    }
  }
}
package com.tomcat.chapter2;

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);
  }

}
package com.tomcat.chapter2;

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);
  }

}
package com.tomcat.chapter2;

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("servlet." + servletName);
    }
    catch (ClassNotFoundException e) {
      System.out.println(e.toString());
    }

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

  }
}
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