使用jsp：usebean时出现空指针异常

Question

I am getting a Null pointer exception while using the object created by <jsp:usebean> . 使用<jsp:usebean>创建的对象时，出现Null指针异常。 The object has been properly instantiated, ( <jsp:getproperty> is running fine ).But when I pass this created object in static method of Register class,its throwing a Null Pointer Exception. 该对象已正确实例化（ <jsp:getproperty>运行良好）。但是当我在Register类的静态方法中传递此创建的对象时，它引发Null指针异常。

NewFile.htm NewFile.htm

    <!DOCTYPE html>
<html>
<form action="NewFile.jsp">
Name<input type="text" name="textbox1"/>
<br>
ID<input type="text" name="textbox2"/>
<br><select name="select1">
<option>India</option>
<option>France</option>
<option>Japan</option>

</select>
<br>
<input type="submit"/>

</form>
</body>
</html>

NewFile.jsp NewFile.jsp

<%@ page import="com.psl.Register" %>
<jsp:useBean id="emp" class="com.psl.Employee"/>
<jsp:setProperty property="name" name="emp" param="textbox1"/>
<jsp:setProperty property="country" name="emp" param="select1"/>
<jsp:setProperty property="id" name="emp" param="textbox2"/>
<jsp:getProperty property="country" name="emp"/> 
<%Register.register(emp);%>

Register.java Register.java

package com.psl;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class Register {
    public static void register (Employee obj)
    {

        try {
            PreparedStatement stm = DBConnection.establishConnection().prepareStatement("insert into Person values (?,?,?)");
            stm.setString(1,obj.getName() );
            stm.setInt(2, obj.getId());
            stm.setString(3, obj.getCountry());
    stm.execute();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
}

Employee.java Employee.java

package com.psl;

import java.util.Arrays;

public class Employee {



    @Override
    public String toString() {
        return "Employee [name=" + name + ", id=" + id + ", country=" + country
                + "]";
    }

    private String name;
    private int id;
    private String country;


    public Employee() {
        // TODO Auto-generated constructor stub
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getCountry() {
        return country;
    }

    public void setCountry(String country) {
        this.country = country;
    }


}

DBConnection.java DBConnection.java

public class DBConnection {

private static Connection con ;
public static Connection establishConnection()
{try {

    Class.forName("com.mysql.jdbc.Driver");
    con=DriverManager.getConnection("jdbc:mysql://localhost:3306/database","root","root");
    } catch (Exception e) {
        // TODO: handle exception
    }   
return con;

}

} }

Answer 1

Here's your problem. 这是你的问题。

Class.forName("com.mysql.jdbc.Driver");
con=DriverManager.getConnection("jdbc:mysql://localhost:3306/database","root","root");
} catch (Exception e) {
    // TODO: handle exception
}

An Exception is probably being thrown and you are swallowing it, ie. 一个Exception可能是被抛出，你是吞咽，即。 not handling it . 不处理 。 con remains null , but you return it. con保留为null ，但您将其返回。

DBConnection.establishConnection()

therefore returns null . 因此返回null 。

You try to call 您尝试打电话

prepareStatement("insert into Person values (?,?,?)");

on null . 在null 。

Don't use scriptlets. 不要使用脚本。

Answer 2

The codes looks fine but thr may be two below reason to get null pointer exception . 代码看起来不错，但是thr可能是以下两个导致null pointer exception原因。 As you are getting the connection from method DBConnection.establishConnection() so check this is providing proper and valid connection. 当您从方法DBConnection.establishConnection()获取connection ，请检查此连接是否提供正确且有效的连接。

The other thing can be Employee obj , the obj can be null ,as you are calling it from .jsp so check it. 另一件事可以是Employee obj ， obj可以为null ，因为您是从.jsp调用的，因此请检查它。

使用jsp：usebean时出现空指针异常

问题描述

2 个解决方案

解决方案1
1 已采纳 2014-02-02 17:53:26

解决方案2
0 2014-02-02 18:05:04

使用jsp：usebean时出现空指针异常

问题描述

2 个解决方案

解决方案1 1 已采纳 2014-02-02 17:53:26

解决方案2 0 2014-02-02 18:05:04

解决方案1
1 已采纳 2014-02-02 17:53:26

解决方案2
0 2014-02-02 18:05:04