Question

您好我写了这个java webservice但是我从executeFetchQuery中得到了一个NullPointerException？造成这个NullPointer的原因是什么。我认为由于此错误无法建立连接：错误executeFetchQuery：java.lang.NullPointerException

package nl.jorisdek.dinnerspinner.business;

import java.sql.*;
import java.util.ArrayList;
import javax.sql.DataSource;
import javax.annotation.Resource;
import javax.ejb.LocalBean;
import javax.ejb.Stateless;

/**
 *
 * @author Joris
 */
@Stateless
@LocalBean
public class DbConnect {
    @Resource(name = "jdbc/dinnerspinner")
    private DataSource ds;
    private Statement st;
    private PreparedStatement pst;

    public DbConnect(){
    }

    public void executeModifyQuery(String sql) {
         try{
            Connection con = ds.getConnection();
            con.createStatement().execute(sql);
            con.close();
        } catch(Exception ex) {
            System.out.println("Error: "+ ex);
        }
    }

     public ResultSet executeFetchQuery(String sql) {
        ResultSet rs = null;
        try {
            Connection con = ds.getConnection();
            rs = con.createStatement().executeQuery(sql);
            con.close();
        }
        catch(Exception ex) {
            System.out.println("Error executeFetchQuery: "+ ex);
        }
         System.out.println("rs: "+rs);
        return rs;
    }



    public ArrayList<Dishes> getDishes() {
        //Map json = new HashMap(); 

        ArrayList<Dishes> dishes = new ArrayList<>();
        String sql = "SELECT * FROM dishes";
        ResultSet rs = executeFetchQuery(sql);
        //ResultSetMetaData metaData = rs.getMetaData();
        try {            
            while(rs.next()){
                Dishes dish = new Dishes();

                dish.setId(rs.getInt("id"));
                dish.setNaam(rs.getString("naam"));
                dish.setWinkel(rs.getString("winkel"));
                dish.setIngredienten(rs.getString("ingredienten"));
                dish.setExtra(rs.getString("extra"));
                dish.setKosten(rs.getDouble("kosten"));
                dish.setBereiding(rs.getString("bereiding"));
                dish.setGezond(rs.getBoolean("gezond"));
                dish.setGoedkoop(rs.getBoolean("goedkoop"));
                dish.setSimpel(rs.getBoolean("simpel"));
                dish.setSnel(rs.getBoolean("snel"));

                dishes.add(dish);

            }
        } catch(Exception ex) {
            System.out.println("Error getDishes: "+ ex);
        }

        return dishes;
    }

}

我认为你需要这个

 java.lang.NullPointerException
    at nl.jorisdek.dinnerspinner.DishesSoap.getDishes(DishesSoap.java:35)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

Answer 1

对不起伙计们，

我认为我的错误在于DbConnect。但这是我的DishesSoap。

package nl.jorisdek.dinnerspinner;

import nl.jorisdek.dinnerspinner.business.*;
import java.util.ArrayList;
import javax.ejb.EJB;
import javax.jws.WebService;




@WebService
public class DishesSoap {
    
    private DbConnect dishesDao;

    public ArrayList<Dishes> getDishes() {
        //System.out.println("DishesSOAP: " + dishesDao.getDishes());
        return dishesDao.getDishes();  // line 35
    }

Answer 2

private DbConnect dishesDao;

public ArrayList<Dishes> getDishes() {
    //System.out.println("DishesSOAP: " + dishesDao.getDishes());
    return dishesDao.getDishes();  // line 35
}

dishesDao是null，因为它从未设置过，但是在这里你尝试调用一个方法：

dishesDao.getDishes();

不要那样做。在尝试调用方法

之前，为之前的指定一个可行的参考。

为什么ResultSet有NullPointerException？

2 个答案: