JSF与数据库的交互

以下bean的数据库相关代码正在简单的Java应用程序中工作，但是当我在JSF页面中使用它时，它给出Java空指针异常错误。在此先感谢。JSF与数据库的交互

Bean类： -

import java.io.Serializable; 
import javax.faces.bean.ManagedBean; 
import javax.faces.bean.SessionScoped; 
import java.sql.Connection; 
import java.sql.DriverManager; 
import java.sql.PreparedStatement; 
@ManagedBean 
@SessionScoped  

public class Db implements Serializable{ 
    int eId; 
    public int geteId() { 
     return eId; 
    } 
    public void seteId(int eId) { 
     this.eId = eId; 
    } 
    public static Connection getConnection() throws Exception { 
     String driver = "oracle.jdbc.driver.OracleDriver"; 
     String url = "jdbc:oracle:thin:@localhost:1521:globldb3"; 
     String username = "scott"; 
     String password = "tiger"; 
     Class.forName(driver); 
     Connection conn = DriverManager.getConnection(url, username, password); 
     return conn; 
     } 
    public String addEmployee() throws Exception{ 
     Connection conn = null; 
     PreparedStatement pstmt = null; 
      try { 
        int a = this.eId; 
        conn = getConnection(); 
        String query = "INSERT INTO c(n) VALUES(?)"; 
        pstmt = conn.prepareStatement(query); 
        pstmt.setInt(1,a); 
        pstmt.executeUpdate(); // execute insert statement 
        return "success"; 
       } catch (Exception e) { 
         e.printStackTrace(); 
         return "failure"; 
       } finally { 
         pstmt.close(); 
         conn.close(); 
       } 
    }  
}

以下是我的JSF页面

<html xmlns="http://www.w3.org/1999/xhtml" 
xmlns:ui="http://java.sun.com/jsf/facelets" 
xmlns:h="http://java.sun.com/jsf/html" 
xmlns:f="http://java.sun.com/jsf/core"> 
<body> 
    <h:form> 
    <p>Enter value <h:inputText value="#{db.eId}"/> </p> 
    <p> <h:commandButton value="Add record" action="#{db.addEmployee}"/> </p> 
    </h:form> 
</body> 
</html>

以下是堆栈跟踪

javax.faces.el.EvaluationException: java.lang.NullPointerException 
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:102) 
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102) 
    at javax.faces.component.UICommand.broadcast(UICommand.java:315) 
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:787) 
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1252) 
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81) 
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) 
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118) 
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:312) 
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:306) 
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) 
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240) 
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161) 
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164) 
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:108) 
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:558) 
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) 
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:379) 
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:243) 
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:259) 
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:281) 
    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:619) 
Caused by: java.lang.NullPointerException 
    at erpJavaFiles.Employee.addEmployee(Employee.java:118) 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) 
    at java.lang.reflect.Method.invoke(Method.java:597) 
    at org.apache.el.parser.AstValue.invoke(AstValue.java:262) 
    at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:278) 
    at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105) 
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88) 
    ... 23 more

来源

2011-05-05 Adnan

“NPE”在哪里出现？你能告诉我们堆栈跟踪吗？ – romaintaz 2011-05-05 11:00:17

如果你在'int a = this.eId;'之后做'System.out.println（“a value：”+ a）;'是用某个值填充的吗？ – 2011-05-05 11:01:02

@romaintaz：好吧让我追加堆栈跟踪 – Adnan 2011-05-05 11:03:24

这里，

} finally { 
    pstmt.close(); 
    conn.close(); 
}

在关闭它们之前，您不检查它们是否为null。如果连接时发生异常，他们将保留null。修复它如下：

} finally { 
    if (pstmt != null) pstmt.close(); 
    if (conn != null) conn.close(); 
}

在addEmployee()方法中没有其他潜在的NPE原因。我看到您在catch区块拨打e.printStackTrace()。请阅读本文，了解真实问题的原因。我猜想它是一个ClassNotFoundException上的JDBC驱动程序类，因为你忘了把JDBC驱动程序放在webapp的/WEB-INF/lib文件夹中。

来源

2011-05-05 12:10:47 BalusC

如果@BalusC正确，您可能需要更改您的驱动程序名称：Oracle驱动程序的类名称最近已更改为'oracle.jdbc.OracleDriver'。请参阅http://forums.oracle.com/forums/ann.jspa?annID=201 – 2011-05-05 14:27:41

@Simon：他提到它在作为普通Java应用程序执行时可以工作。 – BalusC 2011-05-05 14:29:25

JSF与数据库的交互

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