获得空指针异常@Resource注释在tomact 7 [英] Getting null pointer exception @Resource annotation in tomact 7

问题描述

下面是我的context.xml Resource元素：

Here is my Resource element in context.xml ::

<Resource name="jdbc/myoracle" auth="Container"
              type="javax.sql.DataSource" driverClassName="oracle.jdbc.driver.OracleDriver"
              url="jdbc:oracle:thin:@localhost:1521:XE"
              username="hr" password="hr" maxActive="20" maxIdle="10"
              maxWait="-1"/> 

下面是在web.xml中我的资源引用：

Here is my Resource reference in web.xml:

       <resource-ref>
            <description>Oracle Datasource</description>
            <res-ref-name>jdbc/myoracle</res-ref-name>
            <res-type>javax.sql.DataSource</res-type>
            <res-auth>Container</res-auth>
        </resource-ref>

然后我用 @Resource 标注在我的code：

      @Resource(mappedName = "jdbc/myoracle")
        DataSource ds;

当我尝试使用的getConnection（）在DS创建连接对象，我在运行时得到一个空指针异常：

When I try to create connection object using getConnection() on ds, I get a null pointer exception during runtime:

    Oct 24, 2011 12:18:21 PM org.apache.catalina.core.StandardWrapperValve invoke
    INFO: java.lang.NullPointerException
        at jdbc.patientDaoImpl.get_patients(patientDaoImpl.java:248)
        at org.apache.jsp.index2_jsp._jspService(index2_jsp.java:92)
        at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
        at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:419)
        at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
        at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:223)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
        at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:563)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:399)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:317)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:204)
        at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:311)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:662)

但是，如果我用查找InitialContext的应用程序工作正常。

But if I lookup using initialContext the app works fine.

    Context initContext = new InitialContext();
    Context envContext  = (Context)initContext.lookup("java:/comp/env");
    DataSource ds = (DataSource)envContext.lookup("jdbc/myoracle");

我在哪里去了？

推荐答案

Tomcat本身并不支持 @Resource 注入。换句话说，servlet容器不能识别的注释，不能用它做任何事情。手工查找的工作，因为资源是正确定义。

Tomcat itself does not support @Resource injection. In other words, the servlet container does not recognize that annotation and can't do anything with it. Manual lookup works, because the resource is defined properly.

您需要一些依赖注入框架：

You need some dependency-injection framework:

• 春季


• CDI（在JavaEE6网络配置文件的一部分）


• EJB（在JavaEE6网络配置文件，不完全是DI框架的一部分）

这篇关于获得空指针异常@Resource注释在tomact 7的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！