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使用java模拟简单的tomcat的方法详解

使用Java模拟简单的Tomcat的方法详解

目的

本文的目的是讲解如何使用Java编写一个简单的Tomcat,以及这个Tomcat的基本原理和用法。

前置知识

在阅读本文之前,你需要掌握一些Java编程基础,如基本语法、OOP思想、多线程等知识。同时,你需要对Tomcat有一定的了解,如Tomcat的工作原理、Servlet容器等。

步骤

步骤一:创建HttpServer类

HttpServer类是整个Tomcat的入口,负责接受并处理请求。

我们需要在HttpServer类中创建一个ServerSocket实例,用于监听HTTP请求。当有一个请求到达时,我们需要使用Socket获取请求信息,然后将请求信息封装到HttpServletRequest对象中,创建HttpServletResponse对象,然后将HttpServletRequest对象和HttpServletResponse对象传递给Servlet。

以下是HttpServer类的一个简单示例:

public class HttpServer {

    public static void main(String[] args) {
        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(8080);
            System.out.println("Tomcat started on port 8080");
            while (true) {
                Socket socket = serverSocket.accept();
                InputStream is = socket.getInputStream();
                OutputStream os = socket.getOutputStream();
                HttpServletRequest request = new HttpServletRequest(is);
                HttpServletResponse response = new HttpServletResponse(os);
                Servlet servlet = ServletContainer.getServlet(request.getRequestURI());
                servlet.service(request, response);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

步骤二:创建HttpServletRequest类

HttpServletRequest类用于封装HTTP请求信息。

我们需要在HttpServletRequest类中解析HTTP请求,获取请求方法、请求路径、请求头和请求体等信息,并将这些信息封装到HttpServletRequest对象中。以下是HttpServletRequest类的一个简单示例:

public class HttpServletRequest {

    private String method;
    private String requestURI;
    private Map<String, String> headers = new HashMap<>();
    private String body;

    public HttpServletRequest(InputStream is) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
        String line = reader.readLine();
        while (line != null && !line.equals("")) {
            if (line.startsWith("GET")) {
                method = "GET";
                requestURI = line.split(" ")[1];
            } else if (line.startsWith("POST")) {
                method = "POST";
                requestURI = line.split(" ")[1];
            } else if (line.startsWith("Content-Length")) {
                int contentLength = Integer.parseInt(line.split(" ")[1]);
                char[] chars = new char[contentLength];
                reader.read(chars, 0, contentLength);
                body = new String(chars);
            } else {
                String[] header = line.split(": ");
                headers.put(header[0], header[1]);
            }
            line = reader.readLine();
        }
    }

    public String getMethod() {
        return method;
    }

    public String getRequestURI() {
        return requestURI;
    }

    public String getHeader(String name) {
        return headers.get(name);
    }

    public String getBody() {
        return body;
    }

}

步骤三:创建HttpServletResponse类

HttpServletResponse类用于封装HTTP响应信息。

我们需要在HttpServletResponse类中构建HTTP响应,包括响应头、响应体等信息,并将这些信息写入到OutputStream中。以下是HttpServletResponse类的一个简单示例:

public class HttpServletResponse {

    private OutputStream os;
    private String contentType = "text/html";
    private Map<String, String> headers = new HashMap<>();
    private StringBuilder body = new StringBuilder();

    public HttpServletResponse(OutputStream os) {
        this.os = os;
    }

    public void setContentType(String contentType) {
        this.contentType = contentType;
        setHeader("Content-Type", contentType);
    }

    public void setHeader(String name, String value) {
        headers.put(name, value);
    }

    public void setStatus(int status) throws IOException {
        String statusText = "";
        switch (status) {
            case 200:
                statusText = "OK";
                break;
            case 404:
                statusText = "Not Found";
                break;
        }
        String response = "HTTP/1.1 " + status + " " + statusText + "\r\n";
        write(response);
    }

    public void write(String data) throws IOException {
        body.append(data);
        os.write(data.getBytes());
    }

    public void flushBuffer() throws IOException {
        String response = "HTTP/1.1 200 OK\r\n";
        response += "Content-Type: " + contentType + "\r\n";
        response += "Content-Length: " + body.toString().getBytes().length + "\r\n";
        for (String name : headers.keySet()) {
            response += name + ": " + headers.get(name) + "\r\n";
        }
        response += "\r\n";
        response += body.toString();
        os.write(response.getBytes());
        os.flush();
    }

}

步骤四:创建Servlet接口

Servlet接口是Tomcat中的核心接口,用于处理HTTP请求并生成HTTP响应。

我们需要定义一个Servlet接口,为其定义service方法,其中HttpServletRequest对象和HttpServletResponse对象可以传递到service方法中,Servlet可以获取HttpServletRequest对象中的请求信息,根据请求信息生成HttpServletResponse对象中的响应信息。

以下是Servlet接口的一个简单示例:

public interface Servlet {

    void service(HttpServletRequest request, HttpServletResponse response);

}

步骤五:创建ServletContainer类

ServletContainer类用于创建Servlet实例,根据请求路径获取相应的Servlet实例。

以下是ServletContainer类的一个简单示例:

public class ServletContainer {

    private static Map<String, Servlet> servletMapping = new HashMap<>();

    static {
        servletMapping.put("/hello", new HelloServlet());
    }

    public static Servlet getServlet(String uri) {
        return servletMapping.get(uri);
    }

}

步骤六:创建Servlet实现类

Servlet实现类是具体的处理HTTP请求的类,可以根据请求信息生成HTTP响应信息。

以下是HelloServlet的一个简单示例:

public class HelloServlet implements Servlet {

    @Override
    public void service(HttpServletRequest request, HttpServletResponse response) {
        try {
            response.setContentType("text/html");
            response.setStatus(200);
            response.write("<html><body><h1>Hello World</h1></body></html>");
            response.flushBuffer();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

示例

示例一

在命令行中运行HttpServer类,得到以下输出:

Tomcat started on port 8080

在浏览器中访问http://localhost:8080/hello,得到以下输出:

Hello World

示例二

在命令行中运行HttpServer类,得到以下输出:

Tomcat started on port 8080

使用telnet工具模拟一个HTTP请求:

$ telnet localhost 8080
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
GET /hello HTTP/1.1
Host: localhost:8080

在命令行中得到以下输出:

HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 31

<html><body><h1>Hello World</h1></body></html>

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