使用gson转化数据响应给前端

 

 war
 
    
      jakarta.servlet
      jakarta.servlet-api
      6.0.0
    

    
      com.csdn
      pro03-fruit-optimize
      1.0-SNAPSHOT
    

    
      com.google.code.gson
      gson
      2.10.1
    
  

 

• 我们经常用的有以下两种MIME类型映射 

    
        body
        text/html
    
    
        json
        application/json
    

1、查询水果清单IndexServlet响应给浏览器 json string

package com.csdn.fruit.servlet;
import com.csdn.fruit.dao.FruitDao;
import com.csdn.fruit.dao.impl.FruitDaoImpl;
import com.csdn.fruit.pojo.Fruit;
import com.google.gson.Gson;
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;
import java.io.PrintWriter;
import java.util.List;
@WebServlet("/index")
public class IndexServlet extends HttpServlet {
    private FruitDao fruitDao = new FruitDaoImpl();
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        List fruitList = fruitDao.getFruitList();
        fruitList.stream().forEach(System.out::println);

        //java object ->  java json string
        Gson gson = new Gson();
        String fruitListJsonStr = gson.toJson(fruitList);

        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("application/json;charset=utf-8");
        PrintWriter out = resp.getWriter();
        out.println(fruitListJsonStr);
        out.flush();
    }
}

 ​

 

2、通过水果名查询水果EditServlet响应给浏览器 json string

package com.csdn.fruit.servlet;
import com.csdn.fruit.dao.FruitDao;
import com.csdn.fruit.dao.impl.FruitDaoImpl;
import com.csdn.fruit.pojo.Fruit;
import com.google.gson.Gson;
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;
import java.io.PrintWriter;
@WebServlet("/edit")
public class EditServlet extends HttpServlet {
    FruitDao fruitDao = new FruitDaoImpl();
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        String fname = req.getParameter("fname");
        Fruit fruit = fruitDao.getFruitByFname(fname);
        System.out.println(fruit);

        Gson gson = new Gson();
        String fruitJsonStr = gson.toJson(fruit);
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("application/json;charset=utf-8");
        PrintWriter out = resp.getWriter();
        out.println(fruitJsonStr);
        out.flush();
    }
}

 3、根据水果名修改库存量UpdateServlet响应给浏览器 json string

package com.csdn.fruit.servlet;
import com.csdn.fruit.dao.FruitDao;
import com.csdn.fruit.dao.impl.FruitDaoImpl;
import com.csdn.fruit.pojo.Fruit;
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;
import java.io.PrintWriter;
@WebServlet("/update")
public class UpdateServlet extends HttpServlet {
    private FruitDao fruitDao = new FruitDaoImpl();
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        String fname = req.getParameter("fname");
        Integer fcount = Integer.parseInt(req.getParameter("fcount"));
        fruitDao.updateFruit(new Fruit(0,fname, 0, fcount, null));
        System.out.println("修改成功");

        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("application/json;charset=utf-8");
        PrintWriter out = resp.getWriter();
        out.println("{\"msg\":\"修改成功\"}");
        out.flush();
    }
}

 4、根据水果名删除水果记录DelServlet响应给浏览器 json string

package com.csdn.fruit.servlet;
import com.csdn.fruit.dao.FruitDao;
import com.csdn.fruit.dao.impl.FruitDaoImpl;
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;
import java.io.PrintWriter;
@WebServlet("/del")
public class DelServlet extends HttpServlet {
    FruitDao fruitDao = new FruitDaoImpl();
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        String fname = req.getParameter("fname");
        fruitDao.delFruit(fname);
        System.out.println("删除成功！");

        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("application/json;charset=utf-8");
        PrintWriter out = resp.getWriter();
        out.println("{\"msg\":\"删除成功\"}");
        out.flush();
    }
}

 5、添加水果AddServlet响应给浏览器 json string

package com.csdn.fruit.servlet;
import com.csdn.fruit.dao.FruitDao;
import com.csdn.fruit.dao.impl.FruitDaoImpl;
import com.csdn.fruit.pojo.Fruit;
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;
import java.io.PrintWriter;
@WebServlet("/add")
public class AddServlet extends HttpServlet {
    private FruitDao fruitDao = new FruitDaoImpl();
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        String fname = req.getParameter("fname");
        Integer price = Integer.parseInt(req.getParameter("price"));
        Integer fcount = Integer.parseInt(req.getParameter("fcount"));
        String remark = req.getParameter("remark");
        Fruit fruit = new Fruit(fname, price, fcount, remark);
        fruitDao.addFruit(fruit);
        System.out.println("添加成功！");

        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("application/json;charset=utf-8");
        PrintWriter out = resp.getWriter();
        out.println("{\"msg\":\"添加成功\"}");
        out.flush();
    }
}