Struts中数据库连接期间的java.lang.NullPointerException [英] java.lang.NullPointerException during database conectivity in struts

问题描述

我正在struts中建立数据库连接并得到error:javax.servlet.ServletException: java.lang.NullPointerException，代码:-
config.xml:

Hi, I am making database connectivity in struts and getting error:javax.servlet.ServletException: java.lang.NullPointerException, code:-
config.xml:

<form-beans>
    <form-bean name="DemoTestForm" type="DemoTestForm"/>
</form-beans>
<action-mappings>
    <action input="/index.jsp" name="DemoTestForm" parameter="testMethod" path="/test" scope="request" type="DemoTestAction">
        <forward name="success" path="/welcomeStruts.jsp"/>
        <forward name="fail" path="/Failure.jsp"/>
    </action>
</action-mappings>

DBConnect.java:

DBConnect.java:

import java.sql.*;
public class DBConnect
{
    Connection con=null;
    String result;
    public String checkUser(String name,String pass)
            throws Exception
    {
        try
        {
            Class.forName("oracle.jdbc.driver.OracleDriver");
            con = DriverManager.getConnection
                    ("jdbc:oracle:thin@localhost:1521:xe", "system", "java");
        }catch(ClassNotFoundException cnf)
        {
            cnf.getMessage();
        }
        finally
        {
            con.close();
        }
        return(result);
    }
}

DemoAction.java:

DemoAction.java:

public class DemoTestAction
        extends org.apache.struts.action.Action {
    @Override
    public ActionForward execute(ActionMapping mapping,
            ActionForm form,
            HttpServletRequest request,
            HttpServletResponse response)
            throws Exception {
        DemoTestForm f = (DemoTestForm)form;
        String name = f.getTextName();
        String pass = f.getTextPass();
        String logic=null;
        DBConnect db=new DBConnect();
        db.checkUser(name, pass);
        Statement stmt=null;
        ResultSet rs=null;
        stmt=db.con.createStatement();
        rs=stmt.executeQuery("select * from admin");
        while (rs.next())
        {
            pass.equals(rs.getString(3))))
            if (name.equals(rs.getString(2)) && pass.equals(rs.getString(3))) {
                logic="success";
                break;
            }
            else
            {
                logic="fail";
            }
        }
        return mapping.findForward(logic);
    }
}

index.jsp:

index.jsp:

<html:form action="/test">
 Name: <html:text property="textName"/><br>
 Password:   <html:password property="textPass"/><br>
 <html:submit property="loginButton" value="Login Here"/>
 </html:form

>

请帮助解决我的问题.

Please help solve my problem.

推荐答案

请看以下代码:

Look at the following code:

try {
    Class.forName("oracle.jdbc.driver.OracleDriver");
    con = DriverManager.getConnection
            ("jdbc:oracle:thin@localhost:1521:xe", "system", "java");
}
catch (ClassNotFoundException cnf) {
    cnf.getMessage();
}
finally
{
    con.close();
}
return(result);

每次执行代码时，都会执行finally块.它在try块之后需要清理，并且无论是否存在异常都将执行.

因此，在打开数据库连接后，请关闭它.

另外，即使不使用它，也不会设置result.

Every time the code is executed the finally block is executed. It is there to clean up after a try block and is executed irrespective of if there has been an exception or not.

So after opening a DB connection you close it.

Also, even though it''s not used, result is not being set.

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