一个简单的Servlet容器实现

　　上篇写了一个简单的Java web服务器实现，只能处理一些静态资源的请求，本篇文章实现的Servlet容器基于前面的服务器做了个小改造，增加了Servlet请求的处理。

1. 创建一个ServerSocket对象；
2. 调用ServerSocket对象的accept方法，等待连接，连接成功会返回一个Socket对象，否则一直阻塞等待；
3. 从Socket对象中获取InputStream和OutputStream字节流，这两个流分别对应request请求和response响应；
4. 处理请求：读取InputStream字节流信息，转成字符串形式，并解析，这里的解析比较简单，仅仅获取uri(统一资源标识符)信息;
5. 处理响应（分两种类型，静态资源请求响应或servlet请求响应）：如果是静态资源请求，则根据解析出来的uri信息，从WEB_ROOT目录中寻找请求的资源资源文件, 读取资源文件，并将其写入到OutputStream字节流中；如果是Servlet请求，则首先生成一个URLClassLoader类加载器，加载请求的servlet类，创建servlet对象，执行service方法（往OutputStream写入响应的数据）；
6. 关闭Socket对象；
7. 转到步骤2，继续等待连接请求；

代码实现：

添加依赖：

        <!-- https://mvnrepository.com/artifact/javax.servlet/servlet-api -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.3</version>
        </dependency>

服务器代码：

package ex02.pyrmont.first;

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

import ex02.pyrmont.Request;
import ex02.pyrmont.Response;
import ex02.pyrmont.StaticResourceProcessor;

public class HttpServer1 {

    // 关闭服务命令
    private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";

    public static void main(String[] args) {
        HttpServer1 server = new HttpServer1();
        //等待连接请求
        server.await();
    }

    public void await() {
        ServerSocket serverSocket = null;
        int port = 8080;
        try {
            //服务器套接字对象
            serverSocket = new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }

        // 循环等待请求
        while (true) {
            Socket socket = null;
            InputStream input = null;
            OutputStream output = null;
            try {
                //等待连接，连接成功后，返回一个Socket对象
                socket = serverSocket.accept();
                input = socket.getInputStream();
                output = socket.getOutputStream();

                // 创建Request对象并解析
                Request request = new Request(input);
                request.parse();
                // 检查是否是关闭服务命令
                if (request.getUri().equals(SHUTDOWN_COMMAND)) {
                    break;
                }
                
                // 创建 Response 对象
                Response response = new Response(output);
                response.setRequest(request);

                if (request.getUri().startsWith("/servlet/")) {
                    //请求uri以/servlet/开头，表示servlet请求
                    ServletProcessor1 processor = new ServletProcessor1();
                    processor.process(request, response);
                } else {
                    //静态资源请求
                    StaticResourceProcessor processor = new StaticResourceProcessor();
                    processor.process(request, response);
                }

                // 关闭 socket
                socket.close();

            } catch (Exception e) {
                e.printStackTrace();
                System.exit(1);
            }
        }
    }
}

常量类：

package ex02.pyrmont;

import java.io.File;

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

Request：

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;
    }
    /**
     * 
     * requestString形式如下：
     * GET /index.html HTTP/1.1
     * Host: localhost:8080
     * Connection: keep-alive
     * Cache-Control: max-age=0
     * ...
     * 该函数目的就是为了获取/index.html字符串
     */
    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;
    }
    //从InputStream中读取request信息，并从request中获取uri值
    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 {
    }

}

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