0、綜合案例功能介紹

以上是在綜合案例要實作的功能，除了對資料的增刪改查功能之外，還有一些復雜的功能，如批量洗掉，分頁查詢，條件查詢等功能
- 批量洗掉功能：每條資料前都有復選框，當我們選中多條資料并點擊批量洗掉按鈕后，會發送請求到后端并洗掉資料庫指定的多條資料
- 分頁查詢功能：當資料庫中有很多資料的時候，我們不可能將所有的資料展示在一頁里，這個時候就需要分頁展示資料
- 條件查詢功能：資料庫量大的時候，我們需要精確的查詢一些想看到的資料，這個時候就需要通過條件查詢

1、查詢所有功能

整體流程如下圖所示

1.1、后端實作

1.1.1、dao方法實作

在com.coolman.mapper.BrandMapper介面中定義抽象方法，使用@Select注解撰寫SQL陳述句

// 查詢所有品牌
    @Select("select * from brand.tb_brand order by ordered")
    List<Brand> selectAllBrands();

由于表中有些欄位名和物體類中的屬性名沒有對應，所以要進行相關配置

方法1：在SQL陳述句中取別名

// 查詢所有品牌
    @Select("select id, brand_name as brandName, company_name as companyName, ordered, description, status from brand.tb_brand order by ordered")
    List<Brand> selectAllBrands();

方法2：在BrandMapper.xml映射組態檔中定義結果映射，同時在使用注解開發的條件下在Mapper介面中使用ResultMap注解

<resultMap id="brandResultMap" type="Brand">
        <result property="brandName" column="brand_name" />
        <result property="companyName" column="company_name" />
    </resultMap>

//查詢所有品牌
    @Select("select * from brand.tb_brand order by ordered")
    @ResultMap("brandResultMap")
    List<Brand> selectAllBrands();

方法3：在MyBatis組態檔中設定并開啟駝峰自動命名映射

<settings>
  <setting name="mapUnderscoreToCamelCase" value="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/true"/>
</settings>

1.1.2、service實作

// 查詢所有品牌
    public List<Brand> selectAllBrands() {
        SqlSession sqlSession = MyBatisUtils.getSqlSession();

        BrandMapper mapper = sqlSession.getMapper(BrandMapper.class);

        List<Brand> brands = mapper.selectAllBrands();

        sqlSession.close();
        return brands;
    }

1.1.3、Servlet實作

package com.coolman.web.servlet;

import com.alibaba.fastjson.JSON;
import com.coolman.pojo.Brand;
import com.coolman.service.BrandService;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

@WebServlet("/selectAllBrandsServlet")
public class SelectAllBrandsServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 在這里處理請求

        // 呼叫服務，查詢所有
        List<Brand> brands = new BrandService().selectAllBrands();
//        System.out.println(brands);

        // 將List物件轉換為JSON字串，傳遞給前端
        String brandsJson = JSON.toJSONString(brands);

        // 解決中文亂碼問題，宣告字串為JSON字串
        response.setContentType("application/json;charset=utf-8");

        // 回傳JSON字串
        response.getWriter().print(brandsJson);
    }
}

1.2、前端實作

created() {
            axios.get("selectAllBrandsServlet").then( response => {
                // window.alert("正在請求資料");
                // console.log(response.data);
                this.tableData = https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/response.data;
            });
        },

2、添加功能

整體流程如圖所示

2.1、后端實作

2.1.1、dao方法實作

// 添加品牌
    @Insert("insert into brand.tb_brand values(null, #{brandName}, #{companyName}, #{ordered}, #{description}, #{status})")
    void addBrand(Brand brand);

2.1.2、service方法實作

// 添加品牌
    public void addBrand(Brand brand) {
        SqlSession sqlSession = MyBatisUtils.getSqlSession();

        BrandMapper mapper = sqlSession.getMapper(BrandMapper.class);

        mapper.addBrand(brand);

        sqlSession.commit();

        sqlSession.close();
    }

2.1.3、servlet方法實作

package com.coolman.web.servlet;

import com.alibaba.fastjson.JSON;
import com.coolman.pojo.Brand;
import com.coolman.service.BrandService;

import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintStream;

@WebServlet("/addBrandServlet")
public class AddBrandServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 在這里處理請求

        // 獲取ajax請求回傳的json字串
        // 獲取請求體中的輸入流
        ServletInputStream inputStream = request.getInputStream();
        // 呼叫JSON的api將回傳的json字串轉換為物體類物件
        Brand brand = JSON.parseObject(inputStream, Brand.class);

        // 呼叫服務保存資訊
        new BrandService().addBrand(brand);

        response.getWriter().print("ok");
    }
}

2.2、前端實作

在Vue物件中的方法屬性中添加一個功能

// 添加資料
            addBrand(){
                console.log(this.brand);
                axios.post("addBrandServlet", this.brand).then(response => {
                    if (response.data =https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/="ok") {
                        this.dialogVisible = false;
                        window.location.href = "https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/brand.html";
                    } else {
                        window.alert("添加失敗！");
                    }
                })
            },

3、洗掉功能

3.1、后端實作

3.1.1、dao層實作

// 洗掉品牌
    @Delete("delete from brand.tb_brand where id = #{id}")
    void deleteBrand(int id);

3.1.2、service層實作

// 洗掉品牌
    public void deleteBrand(int id) {
        SqlSession sqlSession = MyBatisUtils.getSqlSession();

        BrandMapper mapper = sqlSession.getMapper(BrandMapper.class);

        mapper.deleteBrand(id);

        sqlSession.commit();

        sqlSession.close();
    }

3.1.3、servlet層實作

package com.coolman.web.servlet;

import com.coolman.service.BrandService;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/deleteBrandServlet")
public class DeleteBrandServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 在這里處理請求

        // 獲取回傳的id
        String idStr = request.getParameter("id");
        int id = Integer.parseInt(idStr);

        // 呼叫服務，洗掉該品牌
        new BrandService().deleteBrand(id);

        // 回傳成功洗掉資訊
        response.getWriter().print("ok");
    }
}

3.2、前端實作

在Vue物件的method屬性中添加deleteBrandById方法，同時在html標簽中的點擊事件中，傳遞一個引數回來到方法中

<el-table-column align="center" label="操作">
                <template slot-scope="scope">
                    <el-button type="primary" @click="">修改</el-button>
                    <el-button type="danger" @click="deleteBrandById(scope.row.id)">洗掉</el-button>
                </template>
            </el-table-column>

// 洗掉資料
            deleteBrandById(id){
                // 發送ajax請求
                axios.get("deleteBrandServlet?id=" + id).then( response => {
                    if (response.data =https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/="ok") {
                        // 洗掉成功，跳轉回brand.html
                        window.location.href = "https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/brand.html";
                    } else {
                        window.alert("洗掉失敗");
                    }
                });
            },

4、修改功能

4.1、后端實作

4.1.1、dao層實作

// 修改品牌
    // 回顯功能，根據id查詢品牌資訊
    @Select("select * from brand.tb_brand where id = #{id}")
    Brand selectBrandById(int id);
    // 修改功能
    @Update("update brand.tb_brand set brand_name = #{brandName}, company_name = #{companyName}, ordered = #{ordered}, " +
            "description = #{description},status = #{status} where id = #{id}")
    void updateBrandById(Brand brand);

4.1.2、service層實作

    // 修改品牌
    // 回顯功能
    public Brand selectBrandById(int id) {
        SqlSession sqlSession = MyBatisUtils.getSqlSession();

        BrandMapper mapper = sqlSession.getMapper(BrandMapper.class);

        Brand brand = mapper.selectBrandById(id);

        sqlSession.close();

        return brand;
    }
    // 修改功能
    public void updateBrandById(Brand brand) {
        SqlSession sqlSession = MyBatisUtils.getSqlSession();

        sqlSession.getMapper(BrandMapper.class).updateBrandById(brand);

        sqlSession.commit();
        sqlSession.close();
    }

4.1.3、servlet層實作

回顯功能

package com.coolman.web.servlet;

import com.alibaba.fastjson.JSON;
import com.coolman.pojo.Brand;
import com.coolman.service.BrandService;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/selectBrandByIdServlet")
public class SelectBrandByIdServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 在這里處理請求

        // 接收前端回傳的id
        String idStr = request.getParameter("id");
        int id = Integer.parseInt(idStr);

        // 呼叫服務，查詢品牌資訊
        Brand brand = new BrandService().selectBrandById(id);

        // 將Java物件轉換成json資料，回傳給前端
        String jsonString = JSON.toJSONString(brand);

        // 向前端宣告回傳的資料是json資料，同時更改編碼格式防止編碼錯誤
        response.setContentType("application/json;charset=utf-8");

//        System.out.println(jsonString);
        response.getWriter().print(jsonString);
    }
}

修改功能

package com.coolman.web.servlet;

import com.alibaba.fastjson.JSON;
import com.coolman.pojo.Brand;
import com.coolman.service.BrandService;

import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/updateBrandByIdServlet")
public class UpdateBrandByIdServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 在這里處理請求
        // 接收前端回傳的json資料
        // 得到輸入流
        ServletInputStream inputStream = request.getInputStream();
        // 待用JSON的API轉換成JAVA物件
        Brand brand = JSON.parseObject(inputStream, Brand.class);

        // 呼叫服務，修改資料
        new BrandService().updateBrandById(brand);

        // 回傳修改成功資訊給前端
        response.getWriter().print("ok");
    }
}

4.2、前端實作

//修改資料
            // 點擊修改按鈕后，為了增強用戶體驗，添加一個資料回顯功能
            selectBrandById(id){
                this.dialogVisibleUpdate = true
                // 發送ajax請求
                axios.get("selectBrandByIdServlet?id=" + id).then(response => {
                 // 接收后端回傳的json資料
                 this.brand = response.data;
                 // el-switch開關的默認值必須型別也要匹配~
                 this.brand.status = this.brand.status.toString();
                 console.log(this.brand);
                });
            },
            // 執行修改陳述句
            updateBrandById(id){
                // 發送ajax請求
                axios.post("updateBrandByIdServlet", this.brand).then(response => {
                   if (response.data =https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/="ok") {
                       // 跳轉到brand.html頁面
                       window.location.href = "https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/brand.html";
                   }else {
                       window.alert("修改失敗！")
                   }
                });
            },

5、servlet優化

5.1、背景

Web層的Servlet個數太多，不利于管理和撰寫
- 模塊的每一個功能都需要定義一個servlet，當模塊的數量多時，就很容易造成servlet泛濫，

5.2、解決方法

一個模塊只定義一個servlet，模塊中的每一個功能只需要在servlet中定義對應的方法，如下代碼所示

@WebServlet("/brand/*")
public class BrandServlet {
    //查詢所有
	public void selectAll(...) {}
    
    //添加資料
    public void add(...) {}
    
     //修改資料
    public void update(...) {}
    
    //洗掉洗掉
    public void delete(...) {}
}

5.3、思路

當發送請求至servlet，tomcat會自動呼叫service()方法，原始碼如下所示
- 我們一般在自定義的servlet中會重寫doGet()和doPost()方法，當我們訪問該servlet的時候會根據請求方式將請求分發給doGet()或者doPost()方法
那么可以仿照這樣的請求分發的思想，在service()方法中根據具體的操作呼叫對應的方法
- 如：查詢所有就呼叫selectAll()方法，添加企業資訊就呼叫add()方法

5.4、具體實作

定義一個通用的servlet類，在定義其他的servlet是不需要繼承HttpServlet，而繼承我們定義的BaseServlet，在BaseServlet中呼叫具體servlet（如BrandServlet）中的對應方法，如下所示

BaseServlet

public class BaseServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //進行請求的分發
    }
}

BrandServlet

@WebServlet("/brand/*")
public class BrandServlet extends BaseServlet {
    //用戶實作分頁查詢
	public void selectAll(...) {} 
    
    //添加企業資訊
    public void add(...) {}
    
    //修改企業資訊
    public void update(...) {}
    
    //洗掉企業資訊
    public void delete(...) {}
}

那么如何在BaseServlet中呼叫對應的方法，進行請求分發呢？
- 可以規定在發送請求的時候，請求資源的二級路徑（/brandServlet/selectAll）和需要呼叫的方法名相同，如下所示
  - 查詢所有資料的路徑以后就需要寫成： http://localhost:8080/brand-case/brandServlet/selectAll
  - 添加資料的路徑以后就需要寫成： http://localhost:8080/brand-case/brandServlet/add
  - 修改資料的路徑以后就需要寫成： http://localhost:8080/brand-case/brandServlet/update
  - 洗掉資料的路徑以后就需要寫成： http://localhost:8080/brand-case/brandServlet/delete
- 或者給在路徑中添加一個引數，值為對應的方法名稱，如下所示
  - 查詢所有資料的路徑以后就需要寫成： http://localhost:8080/brand-case/brandServlet?action=selectAll
  - ...
這樣的話，在BaseServlet中就需要獲取到資源的二級路徑作為方法名或者路徑中的action引數的值，然后呼叫該方法

5.4.1、后端代碼

BaseServlet

package com.coolman.web.servlet;

import cn.hutool.core.util.StrUtil;
import com.coolman.web.servlet.BrandServlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class BaseServlet extends HttpServlet {

    @Override
    // tomcat中的servlet每次被呼叫都會執行service方法
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 在這里分發請求
        // 1. 獲取方法名稱
        // 1.1 如果請求的URL格式為 .../brandServlet?action=selectAll

        // 那么獲取方法名稱則要簡單很多
//        String methodName = request.getParameter("action");     // 但是在前端的ajax請求中就需要多寫一些單詞

        // 1.2 如果請求的URL格式為 .../brandServlet/selectAll
        // 使用工具類，獲取到最后一個'/'號后面的字串
        // 1.2.1 獲取請求的URI
        String requestURI = request.getRequestURI();
        // 1.2.2 使用工具類，獲取到最后一個'/'號后面的字串
        String methodName = StrUtil.subAfter(requestURI, "/", true);

        // 2. 獲取方法名稱后呼叫方法
        // 方式1：
//        if ("selectAll".equals(methodName)) {
//            selectAll(request, response);
//        } else if ("add".equals(methodName)) {
//            add(request, response);
//        } else if ("delete".equals(methodName)) {
//            delete(request, response);
//        } else if ("update".equals(methodName)) {
//            update(request, response);
//        } //else if ...

        // 方式2: 方式1在當功能多的時候就會顯地條件判斷很冗余
        //  可以利用反射的方法,獲取到方法,然后呼叫對應的方法即可
        try {
            Method method = this.getClass().getDeclaredMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            // 再讓方法物件執行
            // 暴力反射獲取位元組碼物件的時候需要去除權限(在同一個包下,protected是可以訪問的)
//            method.setAccessible(true);
            method.invoke(this, request, response);
        } catch (Exception e) {
            e.printStackTrace();
        }
//        catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
//            e.printStackTrace();
//        }

    }
}

BrandServlet

package com.coolman.web.servlet;

import com.alibaba.fastjson.JSON;
import com.coolman.pojo.Brand;
import com.coolman.service.BrandService;

import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

@WebServlet("/brand/*") // 不帶action
//@WebServlet("/brand") // 帶action
public class BrandServlet extends BaseServlet {
    // 查詢所有品牌
    protected void selectAll(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 呼叫服務，查詢所有
        List<Brand> brands = new BrandService().selectAllBrands();
//        System.out.println(brands);

        // 將List物件轉換為JSON字串，傳遞給前端
        String brandsJson = JSON.toJSONString(brands);

        // 解決中文亂碼問題，宣告字串為JSON字串
        response.setContentType("application/json;charset=utf-8");

        // 回傳JSON字串
        response.getWriter().print(brandsJson);
    }

    // 添加品牌
    protected void add(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 獲取ajax請求回傳的json字串
        // 獲取請求體中的輸入流
        ServletInputStream inputStream = request.getInputStream();
        // 呼叫JSON的api將回傳的json字串轉換為物體類物件
        Brand brand = JSON.parseObject(inputStream, Brand.class);

        // 呼叫服務保存資訊
        new BrandService().addBrand(brand);

        response.getWriter().print("ok");
    }

    // 洗掉品牌
    protected void delete(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 獲取回傳的id
        String idStr = request.getParameter("id");
        int id = Integer.parseInt(idStr);

        // 呼叫服務，洗掉該品牌
        new BrandService().deleteBrand(id);

        // 回傳成功洗掉資訊
        response.getWriter().print("ok");
    }

    // 根據id查詢品牌
    protected void selectBrandById(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 接收前端回傳的id
        String idStr = request.getParameter("id");
        int id = Integer.parseInt(idStr);

        // 呼叫服務，查詢品牌資訊
        Brand brand = new BrandService().selectBrandById(id);

        // 將Java物件轉換成json資料，回傳給前端
        String jsonString = JSON.toJSONString(brand);

        // 向前端宣告回傳的資料是json資料，同時更改編碼格式防止編碼錯誤
        response.setContentType("application/json;charset=utf-8");

//        System.out.println(jsonString);
        response.getWriter().print(jsonString);
    }

    // 修改品牌資訊
    protected void update(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 接收前端回傳的json資料
        // 得到輸入流
        ServletInputStream inputStream = request.getInputStream();
        // 待用JSON的API轉換成JAVA物件
        Brand brand = JSON.parseObject(inputStream, Brand.class);

        // 呼叫服務，修改資料
        new BrandService().updateBrandById(brand);

        // 回傳修改成功資訊給前端
        response.getWriter().print("ok");
    }

}

注意事項

BaseServlet和BrandServlet要放在同一個包下，否則因為BrandServlet中的方法全都是protected修飾的方法，必須要設定取出權限才可呼叫
- method.setAccessible(true);

7、批量洗掉

7.1、后端實作

7.1.1、dao層實作

BrandMapper.java

// 批量洗掉
    void deleteByIds(@Param("ids") int[] ids);

BrandMapper.xml

<delete id="deleteByIds">
        delete from brand.tb_brand where id in
        <foreach collection="ids" separator="," open="(" close=")" item="id">
            #{id}
        </foreach>
    </delete>

7.1.2、service層實作

    // 批量洗掉功能
    public void deleteByIds(int[] ids) {
        SqlSession sqlSession = MyBatisUtils.getSqlSession(true);
        BrandMapper mapper = sqlSession.getMapper(BrandMapper.class);

        mapper.deleteByIds(ids);

        sqlSession.close();
    }

7.1.3、web層servlet實作

    // 批量洗掉
    protected void deleteByIds(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 接收前端回傳的id陣列
        ServletInputStream inputStream = request.getInputStream();
        int[] ids = JSON.parseObject(inputStream, int[].class);

        // 呼叫服務
        new BrandService().deleteByIds(ids);

        // 回傳成功資訊
        response.getWriter().print("ok");
    }

7.2、前端實作

body中的標簽系結好事件后，執行事件的方法

       // 批量洗掉資料
       deleteBatch() {
           this.$confirm("確定要洗掉嗎?","提示", {
               confirmButtonText: "確定",
               cancelButtonText: "取消",
               type: "warning"
           }).then( () => {
               // 點擊確定按鈕后要執行的操作
               // this.$message({
               //     message: "洗掉成功!",
               //     type: "success"
               // });
               let ids = [];
               for (let i = 0; i < this.multipleSelection.length; i++) {
                   // ids[i] = this.multipleSelection[i].id;
                   ids.push(this.multipleSelection[i].id);
               }
               console.log(ids);
               axios.post("brand/deleteByIds", ids).then( response => {
                   if (response.data =https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/="ok") {
                       window.location.href = "https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/brand.html";
                   } else {
                       this.$message({
                           message: "洗掉失敗!",
                           type: "error"
                       });
                   }
               });
           });
       },

8、分頁查詢

8.1、后端實作

8.1.1、dao層實作

// 分頁查詢
    //select * from ... limit 起始索引, 每頁條數
//    select * from tb_brand limit 0, 5;  // 第一頁
//
//    select * from tb_brand limit 5, 5;  // 第二頁
//
//    select * from tb_brand limit 10, 5; // 第三頁

    //select * from ... limit (起始索引 - 1) * 每頁條數, 每頁條數
    @Select("select * from brand.tb_brand limit #{currentPage}, #{pageSize}")
    List<Brand> selectBrandByPage(@Param("currentPage") int currentPage, @Param("pageSize") int pageSize);
    // 頁碼左邊需要的總條數
    @Select("select count(*) from brand.tb_brand")
    Integer selectSumCount();

8.1.2、service層實作

    // 分頁功能
    public PageBean<Brand> selectBrandByPage(int currentPage, int pageSize) {
        //select * from ... limit (起始索引 - 1) * 每頁條數, 每頁條數
        currentPage = (currentPage - 1) * pageSize;

        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        BrandMapper mapper = sqlSession.getMapper(BrandMapper.class);

        List<Brand> brands = mapper.selectBrandByPage(currentPage, pageSize);
        int totalCount = mapper.selectSumCount();

        sqlSession.close();

        return new PageBean<Brand>(totalCount, brands);
    }

8.1.3、web層servlet實作

    // 處理分頁請求
    protected void selectBrandByPage(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 接收前端回傳的頁碼數
        // pageSize
        int pageSize = Integer.parseInt(request.getParameter("pageSize"));

        // currentPage
        int currentPage = Integer.parseInt(request.getParameter("currentPage"));

        // 呼叫服務
        PageBean<Brand> pageBean = new BrandService().selectBrandByPage(currentPage, pageSize);

        // 回傳資料
        String string = JSON.toJSONString(pageBean);
        response.setContentType("application/json;charset=utf-8");
        response.getWriter().print(string);
    }

8.2、前端實作

created()函式

created() {
            axios.get("brand/selectBrandByPage?currentPage=" + this.currentPage + "&pageSize=" + this.pageSize).then( response => {
                // window.alert("正在請求資料");
                // console.log(response.data);
                this.totalCount = response.data.totalCount;
                this.tableData = https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/response.data.list;
            });
        }

handleSizeChange(val)函式(每一頁的資料量)

handleSizeChange(val) {
                console.log(`每頁 ${val} 條`);
                this.pageSize = val;
                axios.get("brand/selectBrandByPage?currentPage=" + this.currentPage + "&pageSize=" + this.pageSize).then( response => {
                    // window.alert("正在請求資料");
                    // console.log(response.data);
                    this.tableData = https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/response.data.list;
                });

            }

handleCurrentChange(val)函式(當前頁碼)

handleCurrentChange(val) {
                console.log(`當前頁: ${val}`);
                this.currentPage = val;
                axios.get("brand/selectBrandByPage?currentPage=" + this.currentPage + "&pageSize=" + this.pageSize).then( response => {
                    // window.alert("正在請求資料");
                    // console.log(response.data);
                    this.tableData = https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/response.data.list;
                });
            }

9、條件查詢

9.1、后端實作

9.1.1、dao層實作

Mapper介面

// 多條件查詢
    List<Brand> selectBrandByCondition(@Param("brand") Brand brand, @Param("currentPage") int currentPage, @Param("pageSize") int pageSize);
    // 查詢結果記錄數
    int selectSearchCount(Brand brand);

Mapper映射檔案

<select id="selectBrandByCondition" resultMap="brandResultMap">
        select * from brand.tb_brand
        <where>
            <!-- 當狀態碼設定為0或1的時候,很容易出現框架自動轉換成false或true的情況;可以看作一個小bug -->
                <!-- 當傳入的是int型的數字 0 時，mybatis會把它當成空字串
                     status != '', 0 != ''  ==>  '' != ''
                -->
            <if test="brand.status != null">
                status = #{brand.status}
            </if>
            <if test="brand.brandName != null and brand.brandName != ''">
                and brand_name like #{brand.brandName}
            </if>
            <if test="brand.companyName != null and brand.companyName != ''">
                and company_name like #{brand.companyName}
            </if>
        </where>
        order by ordered limit #{currentPage}, #{pageSize}
    </select>

    <select id="selectSearchCount" resultType="java.lang.Integer">
        select count(*) from brand.tb_brand
        <where>
            <if test="status != null">
                status = #{status}
            </if>
            <if test="brandName != null and brandName != ''">
                and brand_name like #{brandName}
            </if>
            <if test="companyName != null and companyName != ''">
                and company_name like #{companyName}
            </if>
        </where>
    </select>

9.1.2、service層實作

    // 多條件查詢
    public PageBean<Brand> selectBrandByCondition(Brand brand, int currentPage, int pageSize) {
        SqlSession sqlSession = MyBatisUtils.getSqlSession();
        BrandMapper mapper = sqlSession.getMapper(BrandMapper.class);

        if (brand.getBrandName() != null && brand.getBrandName().length() > 0) {
            brand.setBrandName("%" + brand.getBrandName() + "%");
        }
        if (brand.getCompanyName() != null && brand.getCompanyName().length() > 0) {
            brand.setCompanyName("%" + brand.getCompanyName() + "%");
        }

        currentPage = (currentPage - 1) * pageSize;
        List<Brand> brands = mapper.selectBrandByCondition(brand, currentPage, pageSize);
      	int count = mapper.selectSearchCount(brand);
        sqlSession.close();
      	return new PageBean<>(count, brands);
    }

9.1.3、web層servlet實作

    // 處理搜索請求
    protected void selectBrandByCondition(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 接收前端回傳的資料
        int currentPage = Integer.parseInt(request.getParameter("currentPage"));
        int pageSize = Integer.parseInt(request.getParameter("pageSize"));

        ServletInputStream inputStream = request.getInputStream();
        Brand brand = JSON.parseObject(inputStream, Brand.class);

        System.out.println("brand = " + brand);

        // 呼叫服務
        PageBean<Brand> brands = new BrandService().selectBrandByCondition(brand, currentPage, pageSize);

        // 回傳資料
        String string = JSON.toJSONString(brands);
        response.setContentType("application/json;charset=utf-8");
        response.getWriter().print(string);
    }

9.2、前端實作

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>商品串列</title>
    <style>
        .el-table .warning-row {
            background: oldlace;
        }

        .el-table .success-row {
            background: #f0f9eb;
        }
    </style>

</head>
<body>
<div id="app">

    <!--搜索表單-->
    <el-form :inline="true" v-model="brand" >

        <el-form-item label="當前狀態">
            <el-select v-model="brand.status" placeholder="當前狀態">
                <el-option label="啟用" value="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/1"></el-option>
                <el-option label="禁用" value="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/0"></el-option>
            </el-select>
        </el-form-item>

        <el-form-item label="企業名稱">
            <el-input v-model="brand.companyName" placeholder="企業名稱"></el-input>
        </el-form-item>

        <el-form-item label="品牌名稱">
            <el-input v-model="brand.brandName" placeholder="品牌名稱"></el-input>
        </el-form-item>

        <el-form-item>
            <el-button type="primary" @click="onSubmit()">查詢</el-button>
        </el-form-item>
    </el-form>

    <!--按鈕-->
    <el-row>
        <el-button type="danger" plain @click="deleteBatch()">批量洗掉</el-button>
        <el-button type="primary" plain @click="dialogVisibleAdd = true">新增</el-button>
    </el-row>

    <!--添加資料對話框表單-->
    <el-dialog
            title="添加品牌"
            :visible.sync="dialogVisibleAdd"
            
            >

        <el-form ref="form" :model="brand" label->
            <el-form-item label="品牌名稱">
                <el-input v-model="brand.brandName"></el-input>
            </el-form-item>

            <el-form-item label="企業名稱">
                <el-input v-model="brand.companyName"></el-input>
            </el-form-item>

            <el-form-item label="排序">
                <el-input v-model="brand.ordered"></el-input>
            </el-form-item>

            <el-form-item label="備注">
                <el-input type="textarea" v-model="brand.description"></el-input>
            </el-form-item>

            <el-form-item label="狀態">
                <el-switch v-model="brand.status"
                           active-value="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/1"
                           inactive-value="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/0"
                ></el-switch>
            </el-form-item>
                    <el-form-item>
              <el-button type="primary" @click="addBrand">提交</el-button>
              <el-button @click="dialogVisibleAdd = false">取消</el-button>
          </el-form-item>
      </el-form>

  </el-dialog>

  <!--修改資料對話框表單-->
  <el-dialog
          title="編輯品牌"
          :visible.sync="dialogVisibleUpdate"
          
  >

      <el-form ref="form" :model="brand" label->
          <el-form-item label="品牌名稱">
              <el-input v-model="brand.brandName"></el-input>
          </el-form-item>

          <el-form-item label="企業名稱">
              <el-input v-model="brand.companyName"></el-input>
          </el-form-item>

          <el-form-item label="排序">
              <el-input v-model="brand.ordered"></el-input>
          </el-form-item>

          <el-form-item label="備注">
              <el-input type="textarea" v-model="brand.description"></el-input>
          </el-form-item>

          <el-form-item label="狀態">
              <el-switch
                      v-model="brand.status"
                      active-value="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/1"
                      inactive-value="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/0"
              ></el-switch>

          </el-form-item>
                  <el-form-item>
              <el-button type="primary" @click="update()">提交</el-button>
              <el-button @click="dialogVisibleUpdate = false">取消</el-button>
          </el-form-item>
      </el-form>

  </el-dialog>

  <!--表格-->
  <template>
      <el-table
              :data="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/tableData"
              style="width: 100%"
              :row-class-name="tableRowClassName"
              @selection-change="handleSelectionChange"
      >
          <el-table-column
                  type="selection"
                  >
          </el-table-column>
          <el-table-column
                  type="index"
                  >
          </el-table-column>

          <el-table-column
                  prop="brandName"
                  label="品牌名稱"
                  align="center"
          >
          </el-table-column>
          <el-table-column
                  prop="companyName"
                  label="企業名稱"
                  align="center"
          >
          </el-table-column>
          <el-table-column
                  prop="ordered"
                  align="center"
                  label="排序">
          </el-table-column>
          <el-table-column
                  prop="description"
                  align="center"
                  label="描述">
          </el-table-column>
          <el-table-column
                  prop="status"
                  align="center"
                  label="當前狀態">
              <template slot-scope="scope">
                  <el-tag type="success" v-if="scope.row.status=='1'">啟用</el-tag>
                  <el-tag type="danger" v-else>禁用</el-tag>
              </template>
          </el-table-column>

          <el-table-column align="center" label="操作">
              <template slot-scope="scope">
                  <el-button type="primary" @click="selectBrandById(scope.row.id)">修改</el-button>
                  <el-button type="danger" @click="deleteBrandById(scope.row.id)">洗掉</el-button>
              </template>
          </el-table-column>

      </el-table>
  </template>

  <!--分頁工具條-->
  <el-pagination
          @size-change="handleSizeChange"
          @current-change="handleCurrentChange"
          :current-page="currentPage"
          :page-sizes="[5, 10, 15, 20]"
          :page-size="pageSize"
          layout="total, sizes, prev, pager, next, jumper"
          :total="totalCount">
  </el-pagination>
    </div>

  <script src="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/js/vue.js"></script>

  <script src="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/js/axios-0.18.0.js"></script>

  <script src="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/element-ui/lib/index.js"></script>

  <link rel="stylesheet" href="https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/element-ui/lib/theme-chalk/index.css">

  <script>
  new Vue({
      el: "#app",
      created() {
          this.selectAll();
      },
      data() {
          return {
              // 當前頁碼
              currentPage: 1,
              // 總資料數
              totalCount: 0,
              // 每一頁的資料數量
              pageSize: 5,

              // 搜索框

              // 添加資料對話框是否展示的標記
              dialogVisibleAdd: false,
              // 修改資料對話框是否展示的標記
              dialogVisibleUpdate: false,

              // 品牌模型資料
              brand: {
                  status: '',
                  brandName: '',
                  companyName: '',
                  id:"",
                  ordered:"",
                  description:""
              },
              // 復選框選中資料集合
              multipleSelection: [],
              // 表格資料
              tableData: [],
              // 頁碼數
          }
      },
      methods: {
          tableRowClassName({row, rowIndex}) {
              if (rowIndex === 1) {
                  return 'warning-row';
              } else if (rowIndex === 3) {
                  return 'success-row';
              }
              return '';
          },
          // 復選框選中后執行的方法
          handleSelectionChange(val) {
              this.multipleSelection = val;
              console.log(this.multipleSelection)
          },
          // 查詢方法
          onSubmit() {
              // console.log("當前頁碼:" + this.currentPage)
              // console.log("每頁數量:" + this.pageSize)
              // console.log("搜索部分資訊:")
              // console.log(this.brand)
              this.selectAll();
          },
          selectAll() {
              axios.post("brand/selectBrandByCondition?currentPage=" + this.currentPage + "&pageSize=" + this.pageSize,
                  this.brand
              ).then( response => {
                  // window.alert("正在請求資料");
                  console.log(response.data);
                  this.totalCount = response.data.totalCount;
                  this.tableData = https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/response.data.list;
              });
          },

          // 添加資料
          addBrand(){
              console.log(this.brand);
              axios.post("brand/add", this.brand).then(response => {
                  if (response.data =https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/="ok") {
                      this.dialogVisible = false;
                      window.location.href = "https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/brand.html";
                  } else {
                      window.alert("添加失敗！");
                  }
              })
          },

          // 洗掉資料
          deleteBrandById(id){
              // 發送ajax請求
              axios.get("brand/delete?id=" + id).then( response => {
                  if (response.data =https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/="ok") {
                      // 洗掉成功，跳轉回brand.html
                      window.location.href = "https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/brand.html";
                  } else {
                      window.alert("洗掉失敗");
                  }
              });
          },

          //修改資料
          // 點擊修改按鈕后，為了增強用戶體驗，添加一個資料回顯功能
          selectBrandById(id){
              this.dialogVisibleUpdate = true
              // 發送ajax請求
              axios.get("brand/selectBrandById?id=" + id).then(response => {
               // 接收后端回傳的json資料
               this.brand = response.data;
               // el-switch開關的默認值必須型別也要匹配~
               this.brand.status = this.brand.status.toString();
               console.log(this.brand);
              });
          },
          // 執行修改陳述句
          update(){
              // 發送ajax請求
              axios.post("brand/update", this.brand).then(response => {
                 if (response.data =https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/="ok") {
                     // 跳轉到brand.html頁面
                     window.location.href = "https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/brand.html";
                 }else {
                     window.alert("修改失敗！")
                 }
              });
          },

          // 批量洗掉資料
          deleteBatch() {
              this.$confirm("確定要洗掉嗎?","提示", {
                  confirmButtonText: "確定",
                  cancelButtonText: "取消",
                  type: "warning"
              }).then( () => {
                  // 點擊確定按鈕后要執行的操作
                  // this.$message({
                  //     message: "洗掉成功!",
                  //     type: "success"
                  // });
                  let ids = [];
                  for (let i = 0; i < this.multipleSelection.length; i++) {
                      // ids[i] = this.multipleSelection[i].id;
                      ids.push(this.multipleSelection[i].id);
                  }
                  console.log(ids);
                  axios.post("brand/deleteByIds", ids).then( response => {
                      if (response.data =https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/="ok") {
                          window.location.href = "https://www.cnblogs.com/OnlyOnYourself-lzw/archive/2022/08/03/brand.html";
                      } else {
                          this.$message({
                              message: "洗掉失敗!",
                              type: "error"
                          });
                      }
                  });
              });
          },

          //分頁
          handleSizeChange(val) {
              console.log(`每頁 ${val} 條`);
              this.pageSize = val;
              this.selectAll();

          },
          handleCurrentChange(val) {
              console.log(`當前頁: ${val}`);
              this.currentPage = val;
              this.selectAll();
          },

      }
  })
      </script>
  </body>
  </html>

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