如何与 Java 客户端的 servlet 通信

Question

我在 Windows 10 上使用 Netbeans 12 开发了一个 servlet。该 servlet 部署在我的机器上的 Apache Tomcat 9.0.39 上，它与 Netbeans IDE 集成。在开发 servlet 时，Netbeans IDE 会自动创建一个包含静态 Html 内容的 index.html 文件，并将该文件放在“src->main->webapp”文件夹下。
客户端向 servlet 发送一个字符串，然后 servlet 反转字符串并将 returns 返回给客户端。但是，我的客户端只能在 servlet 的响应中看到 index.html（上面提到的）的静态内容，而不是 servlet 写入 PrintWriter 对象的反向字符串对象（从 Response.getWriter() ).
这里是index.html的内容：

<!DOCTYPE html>
<html>
    <head>
        <title>My first servlet</title>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    </head>
    <body>
        <h1>Reversing Strings!!!</h1>
        <p> This is index.html page</p>
    </body>
</html>

这里是web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.1" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd">
    <servlet>
        <servlet-name>ReverseString</servlet-name>
        <servlet-class>org.me.servletlearning.ReverseString</servlet-class>
        <init-param>
            <param-name>greeting</param-name>
            <param-value>Hello Tony</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>ReverseString</servlet-name>
        <url-pattern>/reversestring</url-pattern>
    </servlet-mapping>
    <session-config>
        <session-timeout>
            30
        </session-timeout>
    </session-config>
</web-app>

这里是context.xml:

<?xml version="1.0" encoding="UTF-8"?>
<Context path="/reversestring"/>

这是 servlet：

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    String inputString = request.getParameter("reverse_string");
    StringBuilder temp = new StringBuilder(inputString);
    String result = temp.reverse().toString();
    try (PrintWriter out = response.getWriter()) {
        /* TODO output your page here. You may use following sample code. */
        out.println("<!DOCTYPE html>");
        out.println("<html>");
        out.println("<head>");
        out.println("<title>Servlet ReverseString</title>");            
        out.println("</head>");
        out.println("<body>");
        out.println("<h1>Servlet ReverseString at " + request.getContextPath() + "</h1>");
        out.println("<p> The input string: "+inputString+"<br>");
        out.println("The reversed string: "+result+" </p>");
        out.println("</body>");
        out.println("</html>");
    }
}

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}


@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    processRequest(request, response);
}

客户：

public static void writeToURL() {
        try {
            //   need to study and understand servlet
            //   then write to a servelt through a URL object.
            String stringToReverse = URLEncoder.encode("HelloWorld", "UTF-8");
            
            URL url = new URL("http://localhost:8080/reversestring/");
            URLConnection connection = url.openConnection();
            connection.setDoOutput(true);
            
            OutputStreamWriter out = new OutputStreamWriter(
                    connection.getOutputStream());
            out.write("reverse_string=" + stringToReverse);
            out.close();
            
            BufferedReader in = new BufferedReader(
                    new InputStreamReader(
                            connection.getInputStream()));
            String decodedString;
            while ((decodedString = in.readLine()) != null) {
                System.out.println(decodedString);
            }
            in.close();
        } catch (UnsupportedEncodingException ex) {
                    ex.printStackTrace();
        } catch (MalformedURLException ex) {
            ex.printStackTrace();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

客户端从servlet接收到的内容：

<!DOCTYPE html>
<html>
    <head>
        <title>My first servlet</title>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    </head>
    <body>
        <h1>Reversing Strings!!!</h1>
        <p> This is index.html page</p>
    </body>
</html>

我的代码缺少什么？谢谢

Answer 1

您的 webapp 上下文路径是 /reversestring。 string-reversing servlet 在该上下文中的路径 /reversestring 处注册。要向 servlet 发出请求，URL 应该是：

http://localhost:8080/reversestring/reversestring

如何与 Java 客户端的 servlet 通信

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