项目实战：编辑页面加载库存信息-Toy模板网

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注意下面的 param s 必须要加 s ，如果不加 s ，后端接收不到 fid，Integer.parseInt(req.getParameter("fid"))会出现java.lang.NumberFormatException:Cannot parse null string。本人当时出现这个错误检查了一个小时，所以很难发现这个小细节，因为逻辑都是对的。

项目实战：编辑页面加载库存信息,# Tomcat-Servlet,axios,javascript,json,前端,Servlet

1、前端编辑页面加载水果库存信息逻辑edit.js

function $(key) {
    if (key) {
        if (key.startsWith("#")) {
            key = key.substring(1);
            return document.getElementById(key);
        } else {
            let nodeList = document.getElementsByName(key);
            return Array.from(nodeList);
        }
    }
}
let queryString = window.location.search.substring(1)
if(queryString){
    var fid = queryString.split("=")[1]

    window.onload=function(){
        loadFruit(fid)
    }

    loadFruit = function(fid){
        axios({
            method:'get',
            url:'edit',
            params:{
                fid:fid
            }
        }).then(response=>{
            let fruit = response.data.data
            $("#fid").value=fruit.fid
            $("#fname").value=fruit.fname
            $("#price").value=fruit.price
            $("#fcount").value=fruit.fcount
            $("#remark").value=fruit.remark
        })
    }

/*    update=function(){
        let fid = $("#fid").value
        let fname = $("#fname").value
        let price = $("#price").value
        let fcount = $("#fcount").value
        let remark = $("#remark").value
        axios({
            method:'post',
            url:"update",
            data:{
                fid:fid,
                fname:fname,
                price:price,
                fcount:fcount,
                remark:remark
            }
        }).then(response=>{
            if(response.data.flag){
                window.location.href="index.html"
            }
        })
    }*/
}

2、在FruitDao接口中添加通过id查询数据的方法

package com.csdn.fruit.dao;
import com.csdn.fruit.pojo.Fruit;
import java.util.List;
//dao ：Data Access Object 数据访问对象
//接口设计
public interface FruitDao {

    void addFruit(Fruit fruit);

    void delFruit(String fname);

    void updateFruit(Fruit fruit);

    List<Fruit> getFruitList();

    Fruit getFruitByFname(String fname);

    Fruit getFruitByFid(Integer fid);
}

3、在FruitDaoImpl实现类中实现getFruitByFid()方法

package com.csdn.fruit.dao.impl;
import com.csdn.fruit.dao.FruitDao;
import com.csdn.fruit.pojo.Fruit;
import com.csdn.mymvc.dao.BaseDao;
import java.util.List;
public class FruitDaoImpl extends BaseDao<Fruit> implements FruitDao {
    @Override
    public void addFruit(Fruit fruit) {
        String sql = "insert into t_fruit values (0,?,?,?,?)";
        super.executeUpdate(sql, fruit.getFname(), fruit.getPrice(), fruit.getFcount(), fruit.getRemark());
    }
    @Override
    public void delFruit(String fname) {
        String sql = "delete from t_fruit where fname=?";
        super.executeUpdate(sql, fname);
    }
    @Override
    public void updateFruit(Fruit fruit) {
        String sql = "update  t_fruit set fcount=? where fname = ?";
        super.executeUpdate(sql, fruit.getFcount(), fruit.getFname());
    }
    @Override
    public List<Fruit> getFruitList() {
        return super.executeQuery("select * from t_fruit");
    }
    @Override
    public Fruit getFruitByFname(String fname) {
        return load("select * from t_fruit where fname = ?", fname);
    }
    @Override
    public Fruit getFruitByFid(Integer fid) {
        return load("select * from t_fruit where fid=?", fid);
    }
}

4、编写EditServlet类实现前后端数据交互

package com.csdn.fruit.servlet;
import com.csdn.fruit.dao.FruitDao;
import com.csdn.fruit.dao.impl.FruitDaoImpl;
import com.csdn.fruit.dto.Result;
import com.csdn.fruit.pojo.Fruit;
import com.csdn.fruit.util.ResponseUtil;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/edit")
public class EditServlet extends HttpServlet {
    FruitDao fruitDao = new FruitDaoImpl();

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Integer fid = Integer.parseInt(req.getParameter("fid"));
        Fruit fruit = fruitDao.getFruitByFid(fid);
        ResponseUtil.print(resp, Result.OK(fruit));
    }
}

5、用到的工具类

5.1、ResponseUtil工具类

package com.csdn.fruit.util;
import com.csdn.fruit.dto.Result;
import jakarta.servlet.ServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class ResponseUtil {
    public static void print(ServletResponse response, Result result) throws IOException {
        response.setCharacterEncoding("UTF-8");
        response.setContentType("application/json;charset=utf-8");
        PrintWriter out = response.getWriter();
        out.println(GsonUtil.toJson(result));
        out.flush();
    }
}

5.2、GsonUtil工具类

package com.csdn.fruit.util;
import com.google.gson.Gson;
public class GsonUtil {
    public static String toJson(Object obj) {
        //java object ->  java json string
        Gson gson = new Gson();
        return gson.toJson(obj);
    }
}

项目实战：编辑页面加载库存信息,# Tomcat-Servlet,axios,javascript,json,前端,Servlet