Java开发网 - JSF开发中出现java.lang.NullPointerException异常一般会是什么问题？

Topic: JSF开发中出现java.lang.NullPointerException异常一般会是什么问题？

1.JSF开发中出现java.lang.NullPointerException异常一般会是什么问题？

Posted by: flyingis
Posted on: 2005-07-13 18:24

javax.faces.FacesException: #{user.login}: javax.faces.el.EvaluationException: java.lang.NullPointerException
com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:78)
javax.faces.component.UICommand.broadcast(UICommand.java:312)
javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:267)
javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:381)
com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:75)
com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:200)
com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:90)
javax.faces.webapp.FacesServlet.service(FacesServlet.java:197)

2.Re:JSF开发中出现java.lang.NullPointerException异常一般会是什么问题？ [Re: flyingis]

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Posted by: flyingis
Posted on: 2005-07-13 18:25

#{user.login} 这是一个action，这个方法具体是这样的：
public String login() {
try {
doLogin();
}
catch (SQLException ex) {
logger.log(Level.SEVERE, "loginAction", ex);
return "internalError";
}
catch (NamingException ex) {
logger.log(Level.SEVERE, "loginAction", ex);
return "internalError";
}
if (loggedIn)
return "loginSuccess";
else
return "loginFailure";
}

3.Re:JSF开发中出现java.lang.NullPointerException异常一般会是什么问题？ [Re: flyingis]

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Posted by: flyingis
Posted on: 2005-07-13 18:25

其中用到了doLogin()这个方法：
public void doLogin() throws SQLException, NamingException {

Connection conn = DatabaseConn.getConnection("jdbc/mydb");

try {
PreparedStatement passwordQuery = conn.prepareStatement(
"SELECT password from userInfo WHERE name = ?");

passwordQuery.setString(1, name);

ResultSet result = passwordQuery.executeQuery();

if (!result.next()) return;
String storedPassword = result.getString("password");
loggedIn = password.equals(storedPassword.trim());
}
finally {
conn.close();
}
}

4.Re:JSF开发中出现java.lang.NullPointerException异常一般会是什么问题？ [Re: flyingis]	Copy to clipboard
Posted by: flyingis Posted on: 2005-07-13 18:26 页面中的代码，登录确认的按钮： <h:commandButton value="#{msgs.login}" action="#{user.login}"/> 运行后，在输入用户名和密码后，点击登录就会出现上述的异常！大家再帮我分析一下！