如何激活HttpServlet类？基于Heroku部署的GreetServer类运行与GET/POST请求处理配置咨询

Hey there! Let's break this down for you—first off, a critical point: you don't need a public static void main method for your HttpServlet subclass. Servlets are managed components, not standalone Java programs. Their entire lifecycle (instantiation, initialization, handling requests, destruction) is handled by a Servlet container like Tomcat or Jetty. Your GreetServer code looks solid for handling GET/POST requests—now let's get it activated and deployed to Heroku.

There are two standard ways to tell the Servlet container about your class:

1. Annotation-Based Configuration (Servlet 3.0+ Recommended) #

This is the simplest approach. Just add the @WebServlet annotation to your GreetServer class to define its access path:

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.WebServlet; // Don't forget this import!

@WebServlet("/greet") // Clients will access this at http://your-domain/greet
public class GreetServer extends HttpServlet {
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().print("hello client");
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}

2. XML-Based Configuration (Traditional Approach) #

If you're using an older Servlet version or prefer XML, add a web.xml file in your WEB-INF directory with these entries:

<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>GreetServer</servlet-name>
        <servlet-class>your.package.name.GreetServer</servlet-class> <!-- Replace with your full class path -->
    </servlet>

    <servlet-mapping>
        <servlet-name>GreetServer</servlet-name>
        <url-pattern>/greet</url-pattern> <!-- Match the access path you want -->
    </servlet-mapping>
</web-app>

To get this app running on Heroku, follow these steps:

1. Project Structure #

Make sure your project follows the standard Java Web structure:

your-project/
├── src/
│   └── main/
│       ├── java/
│       │   └── your/
│       │       └── package/
│       │           └── GreetServer.java
│       └── webapp/
│           └── WEB-INF/
│               └── web.xml (only if using XML config)
├── pom.xml (Maven) or build.gradle (Gradle)
└── Procfile

2. Maven Configuration (Example) #

If using Maven, update your pom.xml to package as a WAR file and include necessary dependencies:

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>your.package.name</groupId>
    <artifactId>greet-servlet-app</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging> <!-- Critical: packages as a WAR for web deployment -->

    <dependencies>
        <!-- Servlet API: Provided by the Heroku container, so only needed for compilation -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <!-- Maven WAR Plugin to build the WAR file -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.3.2</version>
            </plugin>
            <!-- Heroku Maven Plugin for deployment -->
            <plugin>
                <groupId>com.heroku.sdk</groupId>
                <artifactId>heroku-maven-plugin</artifactId>
                <version>3.0.0</version>
                <configuration>
                    <appName>your-heroku-app-name</appName> <!-- Replace with your app's name -->
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

3. Create a Procfile #

In your project root, make a file named Procfile (no file extension) to tell Heroku how to start the web container. Use one of these commands:

• For Jetty (lightweight, popular for Heroku):

  web: java -jar target/dependency/webapp-runner.jar target/*.war
  

• For Tomcat:

  web: java -jar target/dependency/tomcat-runner.jar target/*.war
  

Note: If using Maven, you'll need to download the runner first: run mvn dependency:copy -Dartifact=com.github.jsimone:webapp-runner:9.0.70.1:jar -DoutputDirectory=target/dependency to get the Jetty runner.

4. Deploy to Heroku #

1. Install the Heroku CLI, then log in: heroku login
2. Initialize a Git repo if you haven't: git init, git add ., git commit -m "Initial servlet app setup"
3. Create your Heroku app: heroku create your-app-name (or make one via the Heroku web dashboard)
4. Push your code to Heroku: git push heroku main

Once deployed, visit https://your-app-name.herokuapp.com/greet—you should see your "hello client" message for both GET and POST requests!

内容的提问来源于stack exchange，提问作者איתן רבינוביץ