实现一个简单的Tomcat

1. Tomcat作用

我们的web应用会运行在Tomcat中，那么显然请求必定是先到达Tomcat的，Tomcat对于请求实际上会进行如下的处理：

• 提供Socket服务：Tomcat的启动，必然是Socket服务，支持http协议。
• 进行请求的分发：一个Tomcat可以为多个web应用提供服务，那么就需要把url下发到不同的web应用。
• 需要将请求和响应封装成request和response：我们在写后端代码的时候都是直接使用request和response的，这是因为Tomcat已经做好了。

下面我们就自己来实现这三步。

2. 实现代码

项目结构：

  src└─mytomcatBookServlet.javaCarServlet.javaMyRequest.javaMyResponse.javaMyServlet.javaMyTomcat.javaServletMapping.javaServletMappingConfig.java

2.1 封装http请求和响应

package mytomcat;import java.io.IOException;
import java.io.InputStream;/*** 封装http请求*/
public class MyRequest {private String url;private String method;public MyRequest(InputStream inputStream) throws IOException {String httpRequest = "";byte[] httpRequestBytes = new byte[1024];int length = 0;if((length = inputStream.read(httpRequestBytes)) > 0) {httpRequest = new String(httpRequestBytes, 0, length);}String httpHead = httpRequest.split("\n")[0];url = httpHead.split("\\s")[1];method = httpHead.split("\\s")[0];System.out.println(this.toString());}public String getUrl() {return url;}public void setUrl(String url) {this.url = url;}public String getMethod() {return method;}public void setMethod(String method) {this.method = method;}@Overridepublic String toString() {return "MyRequest -- url:" + url + ",method:" + method;}}

package mytomcat;import java.io.IOException;
import java.io.OutputStream;/*** 封装http响应*/
public class MyResponse {private OutputStream outputStream;public MyResponse (OutputStream outputStream) {this.outputStream = outputStream;}public void write(String content) throws IOException {StringBuffer httpResponse = new StringBuffer();httpResponse.append("HTTP/1.1 200 OK\n").append("Content-Type: text/html\n").append("\r\n").append(content);outputStream.write(httpResponse.toString().getBytes());outputStream.close();}}

2.2 实现不同的Servlet

package mytomcat;
/*** Servlet抽象类*/
public abstract class MyServlet {public abstract void doGet(MyRequest myRequest, MyResponse myResponse);public abstract void doPost(MyRequest myRequest, MyResponse myResponse);public void service(MyRequest myRequest, MyResponse myResponse) {if(myRequest.getMethod().equalsIgnoreCase("POST")) {doPost(myRequest, myResponse);}else if(myRequest.getMethod().equalsIgnoreCase("GET")) {doGet(myRequest, myResponse);}}
}

package mytomcat;import java.io.IOException;/*** 处理操作'书'的http请求*/
public class BookServlet extends MyServlet {@Overridepublic void doGet(MyRequest myRequest, MyResponse myResponse) {try {myResponse.write("[get] book...");}catch(IOException e) {e.printStackTrace();}}@Overridepublic void doPost(MyRequest myRequest, MyResponse myResponse) {try {myResponse.write("[post] book...");}catch(IOException e) {e.printStackTrace();}}}

package mytomcat;import java.io.IOException;/*** 处理操作'车'的http请求*/
public class CarServlet extends MyServlet {@Overridepublic void doGet(MyRequest myRequest, MyResponse myResponse) {try {myResponse.write("[get] car...");}catch(IOException e) {e.printStackTrace();}}@Overridepublic void doPost(MyRequest myRequest, MyResponse myResponse) {try {myResponse.write("[post] car...");}catch(IOException e) {e.printStackTrace();}}}

2.3 定义Servlet映射POJO类

package mytomcat;public class ServletMapping {private String servletName;private String url;private String className;public ServletMapping(String servletName, String url, String className) {super();this.servletName = servletName;this.url = url;this.className = className;}public String getServletName() {return servletName;}public void setServletName(String servletName) {this.servletName = servletName;}public String getUrl() {return url;}public void setUrl(String url) {this.url = url;}public String getClassName() {return className;}public void setClassName(String className) {this.className = className;}}

2.4 配置Servlet映射关系

package mytomcat;import java.util.ArrayList;
import java.util.List;/*** 配置请求url和处理的servlet的对应关系*/
public class ServletMappingConfig {public static List<ServletMapping> servletMappingList = new ArrayList<>();;static {servletMappingList.add(new ServletMapping("Book", "/book", "mytomcat.BookServlet"));servletMappingList.add(new ServletMapping("Car", "/car", "mytomcat.CarServlet"));}}

2.5 主类

package mytomcat;import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.HashMap;
import java.util.Map;public class MyTomcat {private int port;//保存请求url和处理请求servlet的对应关系private Map<String, String> urlServletMap = new HashMap<String, String>();public MyTomcat(int port) {this.port = port;}public void start() {initServletMapping();ServerSocket serverSocket = null;try {serverSocket = new ServerSocket(port);System.out.println("MyTomcat is start...\n监听端口：" + port);while(true) {System.out.println("等待请求...");Socket socket = serverSocket.accept();InputStream inputStream = socket.getInputStream();OutputStream outputStream = socket.getOutputStream();MyRequest myRequest = new MyRequest(inputStream);MyResponse myResponse = new MyResponse(outputStream);//请求分发disPatch(myRequest, myResponse);socket.close();}}catch(IOException e) {e.printStackTrace();}finally {if(serverSocket != null) {try {serverSocket.close();}catch(IOException e) {e.printStackTrace();}}}}//初始化url和处理的servlet的对应关系private void initServletMapping() {for(ServletMapping servletMapping: ServletMappingConfig.servletMappingList) {urlServletMap.put(servletMapping.getUrl(), servletMapping.getClassName());}}//分发处理请求private void disPatch(MyRequest myRequest, MyResponse myResponse) {String className = urlServletMap.get(myRequest.getUrl());//反射try {Class<MyServlet> myServletClass = (Class<MyServlet>) Class.forName(className);MyServlet myServlet = myServletClass.newInstance();myServlet.service(myRequest, myResponse);}catch(Exception e) {e.printStackTrace();}}public static void main(String[] args) {MyTomcat myTomcat = new MyTomcat(8080);myTomcat.start();}
}

3. 测试

运行MyTomcat主类，然后在浏览器输入http://localhost:8080/car，可以看到返回[get] car...，大功告成。

源码地址：

https://github.com/WangJun-SCU/mytomcat