如何使用 Struts 2 在 Apache Tomcat 应用程序中建立数据库连接 [英] How to make a database connection in application of Apache Tomcat using Struts 2

问题描述

我想在应用程序级别建立数据库连接，所以我想在 Apache Tomcat 服务器的 web.xml 文件中创建连接.我正在使用 Struts2 MVC 框架开发我们的应用程序.实际上我不想在每个 Java 文件上创建数据库连接.如何在应用程序中建立数据库连接?

I want to make database connection at application level, so I want create connection in web.xml file of Apache Tomcat server. I am developing our application using Struts2 MVC framework. Actually I don't want to create database connection at each Java file. How to make a database connection in application?

我正在尝试在 web.xml 中创建连接，但是 Connection conn = ds.getConnection 行显示了类似 java.lang.NullPointerException 的错误();.所有代码都显示在下面

I am trying create a connection in web.xml but a error like java.lang.NullPointerException is being displayed at line Connection conn = ds.getConnection();. All code is being displayed in below

META-INFO/context.xml:

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

<Resource name="jdbc/dbmy" auth="Container" type="javax.sql.DataSource"
           maxActive="50" maxIdle="30" maxWait="10000"
           username="root" password="mysql" 
           driverClassName="com.mysql.jdbc.Driver"
           url="jdbc:mysql://localhost:3306/dbmy"/>
</Context>

lib/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>MY</display-name>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<filter>
<filter-name>struts2</filter-name>
<filter-class>
     org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter
  </filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

<resource-ref>
<description>MySQL Datasource</description>
<res-ref-name>jdbc/dbmy</res-ref-name>
<res-type>javax.sql.DataSource</res-type>
<res-auth>Container</res-auth>
</resource-ref>
</web-app>

我的 Action 类如:

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.annotation.Resource;
import javax.servlet.ServletContext;
import javax.sql.DataSource;

import com.opensymphony.xwork2.*;


public class GEtResponseObject extends ActionSupport {

/**
 * 
 */
private static final long serialVersionUID = 1L;
ServletContext context =null;
PreparedStatement ps =null;
ResultSet rs =null;


@Resource(name="jdbc/dbmy")
private DataSource ds;

public String execute() {       
 try{
     Connection conn = ds.getConnection(); //At this line, A java.lang.NullPointerException error is being occured.
     ps = conn.prepareStatement("select * from dbmy.mytable ");
     rs = ps.executeQuery();
     if (rs.next()) {
        System.out.println(rs.getString("mycolom"));
     }           
 }
 catch(SQLException e)
 {
      e.printStackTrace();       
 }      
  return Action.SUCCESS;
 }
}

推荐答案

把 @Resource 没有意义.如果您需要有关注入资源的更多信息，您应该阅读 教程.而是创建一个 ServletContextListener 并将注释放在那里.关于上下文初始化事件设置上下文属性

Putting @Resource on the action bean property makes no sense. If you need more information about injecting resources you should read a tutorial. Instead create a ServletContextListener and put annotation there. On context initialized event set context attribute

public class MyServletContextListener implements ServletContextListener {

  @Resource(name="jdbc/dbmy")
  private DataSource ds;

  @Override
  public void contextInitialized(ServletContextEvent servletContextEvent) {
    System.out.println("contextInitialized");
    ServletContext context = servletContextEvent.getServletContext();
    context.setAttribute("ds",ds);
  }

  @Override
  public void contextDestroyed(ServletContextEvent servletContextEvent) {
    System.out.println("contextDestroyed");

  }
}

web.xml(应该在WEB-INF中):

web.xml (should be in WEB-INF):

<listener>
  <listener-class>com.servlet.MyServletContextListener</listener-class>
</listener>

现在可以在execute方法中获取数据源

now you can get datasource in the execute method

ds = (DataSource)ServletActionContext.getServletContext().getAttribute("ds");

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