JavaEE 8，Tomcat8.5，错误状态404

Question

我正在尝试制作我的第一个servlet，但是我得到了404状态代码。

web.xml

<?xml version="1.0" encoding="UTF-8"?> 
<web-app 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_4_0.xsd"
     version="4.0">

    <servlet>
        <servlet-name>Hello</servlet-name>
        <servlet-class>Test.Hello</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>Hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

</web-app>

Hello.java

 package Test;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;


public class Hello extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException{
        PrintWriter pw = res.getWriter();
        pw.println("Hello World");
    }
}

我想运行它: localhost:8080/hello

现在它的状态404

“源服务器未找到目标资源的当前表示形式或不愿透露存在的说明。”

我怎么才能解决这个问题？

Answer 1

很奇怪，我注意到你的web.xml在4.0版。您应该能够通过注释使用与Servlet的url映射。

尝试添加如下所示的WebServlet注释@WebServlet("/hello")：

 package Test;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet; //IMPORT THIS ALSO
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet("/hello") //try adding this here
public class Hello extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException{
        PrintWriter pw = res.getWriter();
        pw.println("Hello World");
    }
}

然后删除web.xml中的任何映射，如果使用注释，则不需要这种映射。

<?xml version="1.0" encoding="UTF-8"?> 
<web-app 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_4_0.xsd"
     version="4.0">

//remove servlet and mapping    

</web-app>

如果这不起作用，您可以尝试的另一件事是更改您的版本。例如，将您的web.xml替换为这个(即3.1版)：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1">

</web-app>