如何仿写简易tomcat 实现思路+代码详细讲解

仿写之前，我们要搞清楚都要用到哪些技术

自定义注解，比如Tomcat使用的是@Servlet，我们可以定义一个自己的@MyServlet
构造请求体和返回体，比如tomcat使用HttpRequest，我们可以自己定义myHttpRequest
java去遍历一个指定目录，然后获取到.java文件，再获取到带有@MyServlet注解的类
然后将这个注解里的path和这个类本身映射成map
通过反射去调用该类的方法（doGet、doPost）
还需要用到socket来监听消息，并且对监听到的消息进行处理

第一步：自定义注解

@Target(ElementType.TYPE)
@Documented
@Retention(RetentionPolicy.RUNTIME)
public @interface MyServlet {String path() default "";
}

第二步：定义HttpRequest以及HttpResponse、

public class MyHttpRequest {//定义一个map，用来存放请求体中的参数，key是参数名称，value是参数值public Map<String,String> map = new HashMap<>();public String getParameter(String key){return map.get(key);}
}

public class MyHttpResponse {public OutputStream outputStream;public static final String responsebody = "HTTP/1.1 200+\r\n" + "Content-Type：text/html+\r\n"+ "\r\n";public MyHttpResponse(OutputStream outputStream) {this.outputStream = outputStream;}
}

第三步：遍历整个目录，把Java文件放入list中

    private static void func(File file){File[] files = file.listFiles();String s;for (File file1 : files) {if (file1.isDirectory()){func(file1);}if (file1.isFile()){//取src之后的名字s = file1.toString().split("src")[1];//去掉src后边的第一个\，得到全类名s = s.substring(1);//判断是不是以.java结尾的文件if (s.length() >=5 && s.substring(s.length() - 5).equals(".java")){//把全类名中的\替换成.s = s.replace('\\','.');//去掉后缀名.javas = s.substring(0,s.length()-5);//把类名加入到list中javaclasses.add(s);}}}}

第四步：找出带有Servlet注解的Java文件，并把注解中的path，类对象放入到map中

    public static void getServlet() throws ClassNotFoundException {for (int i = 0; i < javaclasses.size(); i++) {String path = javaclasses.get(i);Class<?> cl = Class.forName(path);if (cl.isAnnotationPresent(MyServlet.class)){servletMap.put(cl.getAnnotation(MyServlet.class).path(),cl);}}}

第五步：创建socket连接

InetAddress localHost = InetAddress.getLocalHost();System.out.println("localhost" + localHost);ServerSocket serverSocket = new ServerSocket(8080, 10, localHost);System.out.println("等待建立连接");Socket server = serverSocket.accept();System.out.println("连接已建立");

第六步：定义线程接收报文

        HttpAcceptThread httpAcceptThread = new HttpAcceptThread(server);Thread accept = new Thread(httpAcceptThread);accept.start();accept.join();

HttpAcceptThread类内容如下：

class HttpAcceptThread implements Runnable{private Socket socket;ArrayList<String> strings = new ArrayList<>();public HttpAcceptThread(Socket socket) {this.socket = socket;}@Overridepublic void run() {System.out.println("开始接收http");try {BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));String s;while ((s = reader.readLine()).length() != 0){try {strings.add(s);System.out.println(s);} catch (Exception e){System.out.println("接收Http进程结束");break;}}System.out.println("接收http进程结束");} catch (IOException e) {e.printStackTrace();}}
}

第七步：处理httprequest，也就是通过反射去调用doGet和doPost方法

这一步有些复杂，尤其是对url切割时，但我给每一步都加了注释，方便理解

GET /address1?a=111&b=222

   private static void requestHttp(Socket socket,String http) throws IOException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {//GET /address1?a=111&b=222（拿获取到的这个url举例）//先通过空格判断是GET还是POSTString requestStyle = http.split(" ")[0];if (requestStyle.equals("GET")){//如果是GET，取空格后面部分，即/address1?a=111&b=222String httpPathAndParameter = http.split(" ")[1];//定义httpPathString httpPath;//创建httpRequest对象MyHttpRequest myHttpRequest = new MyHttpRequest();//通过索引位置判断url里边有没有带？if (httpPathAndParameter.indexOf("?") != -1){//如果有，由于有个/,因此我们要先拿到address1?a=111&b=222这部分httpPath = httpPathAndParameter.substring(1);//获取问号前面部分，即address1，\\作为转义字符使用httpPath = httpPath.split("\\?")[0];System.out.println(httpPath);//获取问号后面部分的所有参数String parameterString = httpPathAndParameter.split("\\?")[1];//使用&分开String[] parameters = parameterString.split("&");for (int i = 0; i < parameters.length; i++) {//把参数及其值仿佛request的map中myHttpRequest.map.put(parameters[i].split("=")[0],parameters[i].split("=")[1]);}} else {//如果不存在？，也就说明不存在参数，我们只需要获取httpPathhttpPath = httpPathAndParameter.substring(1);System.out.println(httpPath);}//创建HttpResponse对象OutputStream outputStream = socket.getOutputStream();MyHttpResponse myHttpResponse = new MyHttpResponse(outputStream);//反射调用doGetClass servletClass = servletMap.get(httpPath);Method doGet = servletClass.getMethod("doGet", MyHttpRequest.class, MyHttpResponse.class);doGet.invoke(servletClass.newInstance(),myHttpRequest,myHttpResponse);} else {//如果不是Get请求，也按照同样的步骤，先取出/address1String httpPath = http.split(" ")[1];//去掉/,只留下address1httpPath = httpPath.substring(1);System.out.println(httpPath);MyHttpRequest myHttpRequest = new MyHttpRequest();OutputStream outputStream = socket.getOutputStream();MyHttpResponse myHttpResponse = new MyHttpResponse(outputStream);//根据httpPath取出类信息Class servletClass = servletMap.get(httpPath);//获取doPost方法Method doPost = servletClass.getMethod("doPost", MyHttpRequest.class, MyHttpResponse.class);//调用doPost方法doPost.invoke(servletClass.newInstance(),myHttpRequest,myHttpResponse);}}

最后一步：把上面这些方法整合起来，在主方法中调用，同时定义好全局变量

public class MyTomcat {//用于存放Java类的全类名public static ArrayList<String> javaclasses = new ArrayList<>();//用于存放Servlet的类对象，其中key是Servlet的url，value是servlet的类对象public static HashMap<String,Class> servletMap = new HashMap<>();public static void main(String[] args) throws ClassNotFoundException, IOException, InterruptedException, InvocationTargetException, NoSuchMethodException, InstantiationException, IllegalAccessException {String inputPath = "D:\\JavaProject\\practice\\src\\tomcat";File file = new File(inputPath);//获取.java后缀文件，并获取全类名func(file);System.out.println(javaclasses);//获取带有servlet注解的类对象，并放到map中。getServlet();System.out.println(servletMap);InetAddress localHost = InetAddress.getLocalHost();System.out.println("localhost" + localHost);ServerSocket serverSocket = new ServerSocket(8080, 10, localHost);System.out.println("等待建立连接");Socket server = serverSocket.accept();System.out.println("连接已建立");//定义线程接收http报文HttpAcceptThread httpAcceptThread = new HttpAcceptThread(server);Thread accept = new Thread(httpAcceptThread);accept.start();accept.join();//处理请求requestHttp(server,httpAcceptThread.strings.get(0));}

然后就可以进行测试了，在测试类上方加上我们已经定义好的@MyServlet注解

@MyServlet(path = "address1")
public class Servlet1 {public void doGet(MyHttpRequest request, MyHttpResponse response) throws IOException {System.out.println("address1 GET响应：");System.out.println("a=" + request.getParameter("a"));System.out.println("\n响应的http如下：");String resp = MyHttpResponse.responsebody + "<!DOCTYPE html>\n" +"<html>\n" +"<head>\n" +"    <meta charset=\"utf-8\" />\n" +"</head>\n" +"<body>\n" +" \n" +"    <form name=\"my_form\" method=\"POST\">\n" +"        <input type=\"button\" value=\"按下\" onclick=\"alert('你按下了按钮')\">\n" +"    </form>\n" +" \n" +"</body>\n" +"</html>";System.out.println(resp);response.outputStream.write(resp.getBytes());response.outputStream.flush();response.outputStream.close();}public void doPost(MyHttpRequest request, MyHttpResponse response) throws IOException {System.out.println("\n响应的http如下：");String resp = MyHttpResponse.responsebody +"{\"sorry\":\"we only respond to method GET now\"},\r\n" +"";System.out.println(resp);response.outputStream.write(resp.getBytes());response.outputStream.flush();response.outputStream.close();}
}

然后启动项目