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。
项目结构：
src
└─mytomcat
BookServlet.java
CarServlet.java
MyRequest.java
MyResponse.java
MyServlet.java
MyTomcat.java
ServletMapping.java
ServletMappingConfig.java
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;
}
@Override
public 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();
}
}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 {
@Override
public void doGet(MyRequest myRequest, MyResponse myResponse) {
try {
myResponse.write("[get] book...");
}catch(IOException e) {
e.printStackTrace();
}
}
@Override
public 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 {
@Override
public void doGet(MyRequest myRequest, MyResponse myResponse) {
try {
myResponse.write("[get] car...");
}catch(IOException e) {
e.printStackTrace();
}
}
@Override
public void doPost(MyRequest myRequest, MyResponse myResponse) {
try {
myResponse.write("[post] car...");
}catch(IOException e) {
e.printStackTrace();
}
}
}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;
}
}
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"));
}
}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();
}
}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：