在 Java Servlet 应用程序中运行后台任务

柔情只为你懂 2023-09-30 09:09 15阅读 0赞

### 1-示例 ###

这是一个模拟后台任务的示例，它在您的 servlet 应用程序下运行。具体来说，它会在某个时间生成**sitemap.xml**文件，该文件位于 Web 应用程序的根目录中。

![0681e3830902919372560957a28a9cf4.png][]

SiteMapGenerator.java

package com.o7planning.example.servlet.listener;
    
    import java.util.concurrent.Executors;
    import java.util.concurrent.ScheduledExecutorService;
    import java.util.concurrent.TimeUnit;
    
    import javax.servlet.ServletContextEvent;
    import javax.servlet.ServletContextListener;
    
    public class SiteMapGenerator implements ServletContextListener {
    
        private ScheduledExecutorService scheduler;
    
        @Override
        public void contextInitialized(ServletContextEvent event) {
            scheduler = Executors.newSingleThreadScheduledExecutor();
            Runnable command = new SiteMapThread(event.getServletContext());
            // Delay 1 Minute to first execution
            long initialDelay = 1;
            TimeUnit unit = TimeUnit.MINUTES;
            // period the period between successive executions
            long period = 60;// 60 Minute!
    
            scheduler.scheduleAtFixedRate(command, initialDelay, period, unit);
        }
    
        @Override
        public void contextDestroyed(ServletContextEvent event) {
            scheduler.shutdownNow();
        }
    
    }

web.xml

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns="http://java.sun.com/xml/ns/javaee"
        xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
        id="WebApp_ID" version="3.0">
        <display-name>ServletListenerExample</display-name>
    
    
    
        <listener>
            <listener-class>com.o7planning.example.servlet.listener.SiteMapGenerator</listener-class>
        </listener>
    
        <welcome-file-list>
            <welcome-file>index.html</welcome-file>
        </welcome-file-list>
    </web-app>

SiteMapThread.java

package com.o7planning.example.servlet.listener;
    
    import java.io.BufferedWriter;
    import java.io.File;
    import java.io.FileWriter;
    import java.io.IOException;
    import java.util.Date;
    
    import javax.servlet.ServletContext;
    
    public class SiteMapThread implements Runnable {
    
        private ServletContext context;
    
        public SiteMapThread(ServletContext context) {
            this.context = context;
        }
    
        @Override
        public void run() {
            System.out.println("Generate sitemap ... " + new Date());
    
            try {
                this.createFile();
            } catch (Exception e) {
                e.printStackTrace();
            }
    
            System.out.println("Finish generation");
        }
    
        private void createFile() throws IOException {
            System.out.println("Generate file sitemap.xml to: "
                    + context.getRealPath(""));
            String path = context.getRealPath("sitemap.xml");
            File file = new File(path);
            BufferedWriter writer = new BufferedWriter(new FileWriter(file));
            writer.write("<?xml version='1.0' ?>");
            writer.write("<urlset xmlns='http://www.sitemaps.org/schemas/sitemap/0.9' "
                    + " xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'  "
                    + " xsi:schemaLocation='http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd'>");
            //
            writer.write("<url>");
            writer.write("<loc>http://o7planning.org</loc>");
            writer.write("<changefreq>daily</changefreq>");
            writer.write("<priority>0.80</priority>");
            writer.write("</url>");
            //
            writer.write("<url>");
            writer.write("<loc>http://o7planning.org/index.html</loc>");
            writer.write("<changefreq>daily</changefreq>");
            writer.write("<priority>0.80</priority>");
            writer.write("</url>");
            //
            writer.write("</urlset>");
            writer.close();
        }
    
    }

查看更多教程：

*  [Java Servlet/Jsp 教程][Java Servlet_Jsp]

[0681e3830902919372560957a28a9cf4.png]: https://img-blog.csdnimg.cn/img_convert/0681e3830902919372560957a28a9cf4.png
[Java Servlet_Jsp]: https://o7planning.org/10979/servlet-jsp