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

1. 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
2. 构造请求体和返回体，比如tomcat使用HttpRequest，我们可以自己定义myHttpRequest
3. 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
4. 然后将这个注解里的path和这个类本身映射成map
5. 通过反射去调用该类的方法（doGet、doPost）
6. 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 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.java
                    s = 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 strings = new ArrayList<>();

    public HttpAcceptThread(Socket socket) {
        this.socket = socket;
    }

    @Override
    public 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POST
        String requestStyle = http.split(" ")[0];
        if (requestStyle.equals("GET")){
            //如果是GET，取空格后面部分，即/address1?a=111&b=222
            String httpPathAndParameter = http.split(" ")[1];
            //定义httpPath
            String 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httpPath
                httpPath = 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doGet
            Class 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/address1
            String httpPath = http.split(" ")[1];
            //去掉/,只留下address1
            httpPath = 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 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 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 + "\n" +
                "\n" +
                "\n" +
                "    \n" +
                "\n" +
                "\n" +
                " \n" +
                "    
\n" +
                "        \n" +
                "    
\n" +
                " \n" +
                "\n" +
                "";
        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

 可以看到本机ip地址，然后通过浏览器地址栏访问

 这样就实现了一个简单的tomcat