Merge branch 'yinshunyu' into dev

尹顺宇学习笔记/尹顺宇11.06作业/尹顺宇11.06EasyExcel学习笔记.md

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+# EasyExcel学习
+
+## 1.环境搭建
+
+``` 
+<dependency>
+    <groupId>com.alibaba</groupId>
+    <artifactId>easyexcel</artifactId>
+    <version>3.1.2</version>
+</dependency>
+```
+
+**项目结构**：
+
+![1762417616189](C:\Users\Administrator\AppData\Roaming\Typora\typora-user-images\1762417616189.png)
+
+
+
+## 2.本地模拟实现
+
+### 1.简单写入excel
+
+第一步：首先创建实体类Employee
+
+> @ExcelProperty(value = "员工id",index = 0)注解就是代表的excel表的表头的每一列的名字
+
+```java
+@Data@Data
+
+@NoArgsConstructor
+@AllArgsConstructor
+public class Employee {
+    @ExcelProperty(value = "员工id",index = 0)
+    private Integer id;
+    @ExcelProperty(value = "员工姓名",index = 1)
+    private String name;
+    @ExcelProperty(value = "入职日期",index = 2)
+    private Date date;
+    @ExcelProperty(value = "员工工资",index = 3)
+    private Double salary;
+}
+```
+
+第二步：创建工具类：用于获取当前文件夹的路径
+
+``` java
+public class TestFileUtil {
+    public static String getPath(){
+        return TestFileUtil.class.getResource("/").getPath().replace("classes/", "");
+    }
+
+    public static void main(String[] args) {
+        System.out.println(getPath());
+    }
+}
+```
+
+第三步：写操作主要代码：
+
+```java 
+public class SimpleWrite {
+
+    //准备测试数据的方法
+    private List<Employee> data(int count) {
+        List<Employee> list = ListUtils.newArrayList();
+        for (int i = 1; i < count; i++) {
+
+            list.add(new Employee(i,"测试数据1"+i,new Date(),6.6*i));
+        }
+        return list;
+    }
+    //快速入门写数据
+    @Test
+    public void write(){
+          String  fileName = TestFileUtil.getPath() + "simpleWrite" + System.currentTimeMillis() + ".xlsx";
+        // 这里 需要指定写用哪个class去写，然后写到第一个sheet，名字为模板 然后文件流会自动关闭
+        EasyExcel.write(fileName, Employee.class).sheet("模板").doWrite(data(10));
+    }
+}
+```
+
+### 2.简单读出excel
+
+只需要一个方法，就可以读出excel表格信息并在控制台打印
+
+```java
+//快速入门读数据
+public class SimpleReader {
+    @Test
+    public void read(){
+ 
+        String fileName = TestFileUtil.getPath() +  "simpleWrite1762401148464.xlsx";
+        // 这里默认每次会读取100条数据 然后返回过来 直接调用使用数据就行
+        // 具体需要返回多少行可以在`PageReadListener`的构造函数设置
+        EasyExcel.read(fileName, Employee.class, new PageReadListener<Employee>(dataList -> {
+            for (Employee demoData : dataList) {
+                System.out.println(demoData);
+            }
+        })).sheet().doRead();
+    }
+}
+```
+
+### 3.批量写入excel
+
+``` java
+public class ManyWrite {
+    //准备测试数据的方法
+    private List<Employee> data(int count) {
+        List<Employee> list = ListUtils.newArrayList();
+        for (int i = 1; i < count; i++) {
+            list.add(new Employee(i,"测试数据1"+i,new Date(),6.6*i));
+        }
+        return list;
+    }
+    //批量写数据
+    @Test
+    public void write(){
+        // 方法2: 如果写到不同的sheet 同一个对象
+        String fileName = TestFileUtil.getPath() + "repeatedWrite" + System.currentTimeMillis() + ".xlsx";
+        // 这里 指定文件
+        try (ExcelWriter excelWriter = EasyExcel.write(fileName, Employee.class).build()) {
+            
+            WriteSheet writeSheet = EasyExcel.writerSheet( "测试数据").build();
+            long t1 =System.currentTimeMillis();
+            // 去调用写入
+            for (int i = 0; i < 100; i++) {
+
+                // 分页去数据库查询数据 这里可以去数据库查询每一页的数据
+                List<Employee> data = data(10000);
+                excelWriter.write(data, writeSheet);
+            }
+            long t2 =System.currentTimeMillis();
+            System.out.println("耗时："+(t2-t1));
+        }
+    }
+}
+```
+
+### 4.读海量数据
+
+读海量数据需要自定义监听器EmployeeListener
+
+```java
+//自定义监听器读数据
+public class EmployeeListener implements ReadListener<Employee> {
+    private ArrayList<Employee> list = new ArrayList<>();
+    private int count = 100;
+    private EmployeeDao dao;
+    public EmployeeListener(EmployeeDao dao) {
+        this.dao = dao;
+    }
+    //每读完一行数据，就会调用此方法
+    @Override
+    public void invoke(Employee employee, AnalysisContext analysisContext) {
+        //将读取的一行数据保存到list中
+        list.add(employee);
+        //判断是不是到达缓存量了
+        if(list.size()>=100){
+            //操作数据库
+            dao.save(list);
+            list = new ArrayList<>(count);
+        }
+    }
+    //读完整个excel之后后调用此方法
+    @Override
+    public void doAfterAllAnalysed(AnalysisContext analysisContext) {
+        if(list.size()>0){
+            //操作数据库
+            dao.save(list);
+            list = new ArrayList<>(count);
+        }
+    }
+}
+```
+
+以下是Dao层模拟数据库操作
+
+```java
+//模拟操作数据库
+public class EmployeeDao {
+    public void save(List<Employee> list){
+        System.out.println(list.size()+"模拟操作数据库");
+
+    }
+}
+```
+
+```java
+//读海量数据
+public class ManyRead {
+    @Test
+    public void read(){
+        String fileName = TestFileUtil.getPath() +  "repeatedWrite1762406295595.xlsx";
+        ExcelReader reader = EasyExcel.read(fileName, Employee.class, new EmployeeListener(new EmployeeDao())).build();
+        ReadSheet sheet = EasyExcel.readSheet().build();
+        reader.read(sheet);
+    }
+}
+```
+
+### 5.使用模板填充Excel表格
+
+首先在模板中用{.}定义好每一列的名称对应什么
+
+![1762415858999](C:\Users\Administrator\AppData\Roaming\Typora\typora-user-images\1762415858999.png)
+
+``` java
+//练习填充数据
+public class FillWriter {
+    //准备测试数据的方法
+    private List<Employee> data(int count) {
+        List<Employee> list = ListUtils.newArrayList();
+        for (int i = 1; i < count; i++) {
+
+            list.add(new Employee(i,"测试数据1"+i,new Date(),6.6*i));
+        }
+        return list;
+    }
+    @Test
+    public void write(){
+        String fileName = TestFileUtil.getPath() + "listFill" + System.currentTimeMillis() + ".xlsx";
+        String templateFileName = TestFileUtil.getPath() + "模板.xlsx";
+        try (ExcelWriter excelWriter = EasyExcel.write(fileName).withTemplate(templateFileName).build()) {
+            WriteSheet writeSheet = EasyExcel.writerSheet().build();
+            long t1 = System.currentTimeMillis();
+            for (int i = 0; i < 100; i++) {
+                excelWriter.fill(data(10000), writeSheet);
+            }
+            long t2 = System.currentTimeMillis();
+            System.out.println("耗时："+(t2-t1));
+        }
+    }
+}
+```
+
+##  3.前后端端实现导入导出Excel
+
+**listener定义**:
+
+```java
+package com.itheima.listener;
+
+import com.alibaba.excel.context.AnalysisContext;
+import com.alibaba.excel.read.listener.ReadListener;
+import com.itheima.domain.Employee;
+import com.itheima.service.EmployeeService;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class EmployeeListener implements ReadListener<Employee> {
+    /**
+     * 批量处理的数据量阈值
+     */
+    private int count = 10000;
+    private EmployeeService dao ;
+    
+    /**
+     * 临时存储读取的数据列表
+     */
+    private List<Employee> list = new ArrayList<>(count);
+
+    public EmployeeListener(EmployeeService dao) {
+        this.dao = dao;
+    }
+    
+    /**
+     * 处理每一行数据
+     * 当读取到一行数据时会调用此方法
+     * @param employee 当前行的员工数据
+     * @param analysisContext 分析上下文
+     */
+    @Override
+    public void invoke(Employee employee, AnalysisContext analysisContext) {
+        list.add(employee);
+        // 当累积的数据量达到阈值时，执行批量插入操作
+        if(list.size()>=count){
+            dao.addData(list);
+            // 重新初始化列表，准备下一批数据
+            list = new ArrayList<>(count);
+        }
+    }
+
+    /**
+     * 所有数据解析完成后的回调方法
+     * 用于处理剩余未达到批量阈值的数据
+     * @param analysisContext 分析上下文
+     */
+    @Override
+    public void doAfterAllAnalysed(AnalysisContext analysisContext) {
+        // 处理最后一批未达到阈值的数据
+        if(list.size()>0){
+            dao.addData(list);
+        }
+    }
+}
+```
+
+**pojo层：**
+
+pojo层和上面定义一致：
+
+```
+@Data
+@NoArgsConstructor
+@AllArgsConstructor
+public class Employee {
+    @ExcelProperty(value = "员工id",index = 0)
+    private Integer id;
+    @ExcelProperty(value = "员工姓名",index = 1)
+    private String name;
+    @ExcelProperty(value = "入职日期",index = 2)
+    private Date date;
+    @ExcelProperty(value = "员工工资",index = 3)
+    private Double salary;
+}
+```
+
+**controller层：**
+
+主要是两个方法，一个上传，一个下载
+
+```java
+@Controller
+@RequestMapping("/")
+public class MyController {
+    @Autowired
+    private EmployeeService service;
+
+    @RequestMapping("/upload")
+    @ResponseBody
+    public void upload(MultipartFile file, HttpServletResponse response) throws IOException {
+        long start = System.currentTimeMillis();
+        EasyExcel.read(file.getInputStream(), Employee.class, new EmployeeListener(service)).sheet().doRead();
+        long end = System.currentTimeMillis();
+        response.setContentType("text/html;charset=utf-8");
+
+        response.getWriter().print("上传成功,共用时："+(end-start));
+
+    }
+
+    @RequestMapping("/download")
+    public void download(HttpServletResponse response) throws IOException {
+        // 这里注意 使用swagger 会导致各种问题，直接用浏览器或者用postman
+        response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
+        response.setCharacterEncoding("utf-8");
+        // 这里URLEncoder.encode可以防止中文乱码 当然和easyexcel没有关系
+        String fileName = URLEncoder.encode("数据库中导出的数据", "UTF-8").replaceAll("\\+", "%20");
+        response.setHeader("Content-disposition", "attachment;filename*=utf-8''" + fileName + ".xlsx");
+        ExcelWriter writer = EasyExcel.write(response.getOutputStream(), Employee.class).build();
+        WriteSheet sheet = EasyExcel.writerSheet("数据").build();
+        writer.write(service.getData(), sheet);
+        writer.close();
+    }
+}
+```
+
+**Service层**
+
+```java
+package com.itheima.service;
+
+import com.itheima.domain.Employee;
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+
+public interface EmployeeService {
+    public List<Employee> getData();
+    public void addData(List<Employee> list);
+}
+```
+
+```java
+package com.itheima.service.impl;
+
+import com.itheima.domain.Employee;
+import com.itheima.mapper.EmployeeMapper;
+import com.itheima.service.EmployeeService;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+
+@Service
+public class EmployeeServiceImpl implements EmployeeService {
+
+    @Autowired
+    private EmployeeMapper dao;
+
+    @Override
+    public List<Employee> getData() {
+        return dao.getData();
+    }
+
+    @Override
+    public void addData(List<Employee> list) {
+        dao.beathInsert(list);
+    }
+}
+```
+
+**Mapper层**
+
+```java
+public interface EmployeeMapper {
+    public void beathInsert(@Param("list") List<Employee> list);
+
+//    @Select("select * from employee ")
+    @Select("select * from employee")
+    @ResultType(Employee.class)
+    List<Employee> getData();
+
+}
+```
+
+
+
+
+
+
+
+​