一个简单的servlet容器

 HttpServer

package com.whatsmars.tomcat.servlet;

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

/**
 * Created by shenhongxi on 16/3/21.
 */
public class HttpServer {

    private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";

    private boolean shutdown = false;

    public static void main(String[] args) {
        HttpServer server = new HttpServer();
        server.await();
    }

    private void await() {
        ServerSocket serverSocket = null;
        int port = 8080;
        try {
            serverSocket = new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));
            System.out.println("Server started!");
        } 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();
                Request request = new Request(input);
                request.parse();

                Response response = new Response(output);
                response.setRequest(request);

                // check if this is a request for a servlet or a static resource
                if (request.getUri().startsWith("/servlet/")) {
                    ServletProcessor processor = new ServletProcessor();
                    processor.process(request, response);
                } else {
                    StaticResourceProcessor processor = new StaticResourceProcessor();
                    processor.process(request, response);
                }

                socket.close();

                shutdown = request.getUri().equals(SHUTDOWN_COMMAND);
            } catch (Exception e) {
                e.printStackTrace();
                continue;
            }
        }
    }
}

  Request

package com.whatsmars.tomcat.servlet;

import javax.servlet.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.util.Enumeration;
import java.util.Locale;
import java.util.Map;

/**
 * Created by shenhongxi on 16/3/21.
 */
public class Request implements ServletRequest {

    private InputStream input;

    private String uri; // 性能考虑，用byte[]

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

    public void parse() {
        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.println(request.toString());
        uri = parseUri(request.toString());
    }

    private String parseUri(String requestStr) {
        // GET /index.html HTTP/1.1
        // Accept: text/plain; text/html
        // ...
        int index1 = requestStr.indexOf(' ');
        int index2;
        if (index1 != -1) {
            index2 = requestStr.indexOf(' ', index1 + 1);
            if (index2 > index1) {
                return requestStr.substring(index1 + 1, index2);
            }
        }
        return null;
    }

    public String getUri() {
        return uri;
    }

    public Object getAttribute(String name) {
        return null;
    }

    public Enumeration<String> getAttributeNames() {
        return null;
    }

    public String getCharacterEncoding() {
        return null;
    }

    public void setCharacterEncoding(String env) throws UnsupportedEncodingException {

    }

    public int getContentLength() {
        return 0;
    }

}

 Response

package com.whatsmars.tomcat.servlet;

import javax.servlet.ServletOutputStream;
import javax.servlet.ServletResponse;
import java.io.*;
import java.util.Locale;

/**
 * Created by shenhongxi on 16/3/21.
 */
public class Response implements ServletResponse {

    private static final int BUFFER_SIZE = 1024;

    Request request;

    OutputStream output;

    PrintWriter writer;

    public void sendStaticResource() throws IOException {
        byte[] bytes = new byte[BUFFER_SIZE];
        FileInputStream fis = null;
        try {
            File file = new File(Constants.WEB_ROOT, request.getUri());
            if (file.exists()) {
                fis = new FileInputStream(file);
                int ch = fis.read(bytes, 0, BUFFER_SIZE);
                while (ch != -1) {
                    output.write(bytes, 0, ch);
                    ch = fis.read(bytes, 0, BUFFER_SIZE);
                }
            } else {
                String errorMsg = "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(errorMsg.getBytes());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fis != null) {
                fis.close();
            }
        }
    }

    public Response(OutputStream output) {
        this.output = output;
    }

    public void setRequest(Request request) {
        this.request = request;
    }

    public String getCharacterEncoding() {
        return null;
    }

    public String getContentType() {
        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;
    }

}

 RequestFacade

package com.whatsmars.tomcat.servlet;

import javax.servlet.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.Enumeration;
import java.util.Locale;
import java.util.Map;

/**
 * Created by shenhongxi on 2016/4/12.
 */
public class RequestFacade implements ServletRequest {

    private ServletRequest request;

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

    public Object getAttribute(String name) {
        return request.getAttribute(name);
    }

    public Enumeration<String> getAttributeNames() {
        return request.getAttributeNames();
    }

}

 ResponseFacade

package com.whatsmars.tomcat.servlet;

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

/**
 * Created by shenhongxi on 2016/4/12.
 */
public class ResponseFacade implements ServletResponse {

    private ServletResponse response;

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

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

    public String getContentType() {
        return null;
    }

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

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

}

 ServletProcessor

package com.whatsmars.tomcat.servlet;

import javax.servlet.Servlet;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.net.URLStreamHandler;

/**
 * Created by shenhongxi on 2016/4/12.
 */
public class ServletProcessor {

    public void process(Request request, Response response) {
        String uri = request.getUri();
        String servletName = uri.substring(uri.lastIndexOf("/") + 1);
        URLClassLoader loader = null;
        try {
            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) {
            E.printStackTrace();
        }

        Class myClass = null;
        try {
            myClass = loader.loadClass(servletName);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

        Servlet servlet = null;
        try {
            servlet = (Servlet) myClass.newInstance();
            RequestFacade requestFacade = new RequestFacade(request);
            ResponseFacade responseFacade = new ResponseFacade(response);
            // 为了安全考虑，除了实现ServletRequest/ServletResponse的方法，
            // Request/Response中的其他公共方法需对servlet隐藏，所以用外观类
            servlet.service((ServletRequest) requestFacade, (ServletResponse) responseFacade);
        } catch (Exception e) {
            e.printStackTrace();
        } catch (Throwable e) {
            e.printStackTrace();
        }
    }
}

 StaticResourceProcessor

package com.whatsmars.tomcat.servlet;

import java.io.IOException;

/**
 * Created by shenhongxi on 2016/4/12.
 */
public class StaticResourceProcessor {

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

  PrimitiveServlet

package com.whatsmars.tomcat.servlet;

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

/**
 * Created by shenhongxi on 2016/4/12.
 */
public class PrimitiveServlet implements Servlet {
    public void init(ServletConfig config) throws ServletException {
        System.out.println("init");
    }

    public ServletConfig getServletConfig() {
        return null;
    }

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

    public String getServletInfo() {
        return null;
    }

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

  Constants

package com.whatsmars.tomcat.servlet;

import java.io.File;

/**
 * Created by shenhongxi on 2016/4/12.
 */
public class Constants {

    public static final String WEB_ROOT = System.getProperty("user.dir") + File.separator + "whatsmars-tomcat/src/main/webapp"; // 资源文件，class文件等
}