一個簡單的servlet容器實現

1. 服務類

創建一個ServerSocket接收客戶端請求，根據請求路徑判定是否爲servlet請求還是請求靜態資源，然後轉發給分別對應的process進行處理

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 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);
      }
    }
  }
}

2. Request請求類（處理客戶端請求數據）

接收Socket中的輸入流參數，然後讀取裏面的數據進行解析，拿到請求的url地址

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.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 {
  }

}

3. Response響應類（響應客戶端請求）

接收socket的輸出流，然後將服務器的一些處理數據通過輸出流返回給客戶端。目前這個類裏面有一個sendStaticResouce方法，目的是將用戶請求的靜態頁面返回給客戶端。

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) {
  }
}

4. Servlet服務類ServletProcessor2

處理來自客戶端的servlet的請求，首先根據當前服務的根目錄創建一個URLClassLoader用來加載servlet服務類，然後根據請求地址，將請求地址中servlet類名取下來，接着，通過URLClassLoader將servlet服務類加載並進行實例化，最後，將包裝過的request和response傳入servlet服務類的service方法進行服務處理操作。

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 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());
    }

  }
}

5. Request包裝類（主要目的就是封裝request對象，避免暴露太多內容）

package ex02.pyrmont;

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);
  }

}

6. Response包裝類（功能與request的相同）

package ex02.pyrmont;

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);
  }

}

7. 靜態資源處理類

package ex02.pyrmont;

import java.io.IOException;

public class StaticResourceProcessor {

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

8. 常量類

package ex02.pyrmont;

import java.io.File;

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