一个简单的servlet容器

web服务器类：

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);
      }
    }
  }
}

servletRequest类：

包括parse与getUri方法。这方法为了对servlet类隐藏，需要实现修饰类RequestFacade。

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 {
    }

}

servletRequest修饰类：

当request传给servlet的service方法时隐藏request的一些私有方法。比如parse方法。

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);
    }

}

servletResopnse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();
        }
    }


    /**
     * 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) {
    }
}

servletResponse修饰类：

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);
    }

}

servlet处理器：

用于处理对servlet资源的http请求。提供process方法，该方法接受2个参数：javax.servlet.ServletRequest与ServletResponse。主要通过调用getRequestUri从URI里取出具体的servlet资源类名。

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());
        }

    }
}

servlet类：

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");
    }

    /**
     * HTTP/1.1 200 OK
     * Server: Microsoft-IIS/4.0
     * Date: Mon, 5 Jan 2004 13:13:33 GMT
     * Content-Type: text/html
     * Last-Modified: Mon, 5 Jan 2004 13:13:12 GMT
     * Content-Length: 125
     *
     * @param request
     * @param response
     * @throws ServletException
     * @throws IOException
     */
    public void service(ServletRequest request, ServletResponse response)
            throws ServletException, IOException {
        System.out.println("from service");
        PrintWriter out = response.getWriter();
        out.println("HTTP/1.1 200 OK");
        out.println("Server: Microsoft-IIS/4.0");
        out.println("Date: Mon, 5 Jan 2004 13:13:33 GMT");
        out.println("Content-Type: text/html");
        out.println("Last-Modified: Mon, 5 Jan 2004 13:13:12 GMT");
        out.println("Content-Length: 125");
        out.println();
        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;
    }

}