Easyexcel写操作

EasyExcel是一个基于Java的简单、省内存的读写Excel的开源项目。在尽可能节约内存的情况下支持读写百M的Excel

项目github地址：https://github.com/alibaba/easyexcel

官网地址：https://easyexcel.opensource.alibaba.com/docs/current/

先吐槽一下，官方文档写的太烂了，缺少依赖、逻辑不清晰、复制到idea很多跑起来报错

写Excel

准备工作

创建项目，在pom文件中添加以下依赖：

    <dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope><exclusions><exclusion><groupId>org.junit.vintage</groupId><artifactId>junit-vintage-engine</artifactId></exclusion></exclusions></dependency><!-- easyexcel 依赖 --><dependency><groupId>com.alibaba</groupId><artifactId>easyexcel</artifactId><version>2.2.7</version></dependency></dependencies>

创建一个实体类，用于写入excel

@Data
public class Student implements Serializable {@ExcelProperty(value = {"学生编号"},order = 10)private Integer id;@ExcelProperty(value = {"学生姓名"},order = 2)private String name;@ExcelProperty(value = {"学生薪水"},order = 1)private Double salary;@ExcelProperty(value = {"学生生日"},order = 11)private Date birthday;
}

最简单的写入

//生成数据
public List<Student> getData() {List<Student> lists = new ArrayList<>();for(int i = 0; i <= 10; i++) {Student student = new Student();student.setId(i + 1);student.setName("李四" + i);student.setBirthday(new Date());student.setSalary(1500.00D);lists.add(student);}return lists;
}//最简单的写入
@Test
void contextLoads() {EasyExcel.write("学生信息表.xlsx", Student.class).sheet().doWrite(getData());
}

PS:一下方法都是有关最简单写入的具体方法解释，不感兴趣的可以跳过

write方法

代码解释：

EasyExcel.write源码如下：两个重载的方法，接收文件名（含路径）或文件名和Excel头文件

，new 了一个ExcelWriterBuilder对象，将pathName或head写入excelWriterBuilder并返回

pathName:文件名
head:写入表格的class对象，如上方Student.class对象

public class EasyExcelFactory {/*** 构建一个Excel写对象** @return*/public static ExcelWriterBuilder write() {return new ExcelWriterBuilder();}/*** 构建一个Excel写对象** @param file 用来写出文件对象*            * @return Excel writer builder*/public static ExcelWriterBuilder write(File file) {return write(file, null);}/*** 构建 Excel写对象** @param file*           用来写出的文件对象* @param head*          写出的数据类型的class对象* @return Excel writer builder*/public static ExcelWriterBuilder write(File file, Class head) {ExcelWriterBuilder excelWriterBuilder = new ExcelWriterBuilder();excelWriterBuilder.file(file);if (head != null) {excelWriterBuilder.head(head);}return excelWriterBuilder;}/*** 构建Excel 写对象*   * @param pathName*           写出的文件路径名* @return Excel writer builder*/public static ExcelWriterBuilder write(String pathName) {return write(pathName, null);}/*** 构建excel 写对象** @param pathName*            写出的文件路径名* @param head*            写出数据的数据类型的class对象* @return Excel writer builder*/public static ExcelWriterBuilder write(String pathName, Class head) {ExcelWriterBuilder excelWriterBuilder = new ExcelWriterBuilder();excelWriterBuilder.file(pathName);if (head != null) {excelWriterBuilder.head(head);}return excelWriterBuilder;}/*** 构建excel写对象** @param outputStream*            写出的输出流对象* @return Excel writer builder*/public static ExcelWriterBuilder write(OutputStream outputStream) {return write(outputStream, null);}/*** 构建excel写对象** @param outputStream*           写出的输出流* @param head*           写出数据的数据类型的class对象* @return Excel writer builder*/public static ExcelWriterBuilder write(OutputStream outputStream, Class head) {ExcelWriterBuilder excelWriterBuilder = new ExcelWriterBuilder();excelWriterBuilder.file(outputStream);if (head != null) {excelWriterBuilder.head(head);}return excelWriterBuilder;}
}

sheet()方法

@Test
void contextLoads() {EasyExcel.write("学生信息表.xlsx", Student.class).sheet().doWrite(getData());
}

sheet()方法代表要在excel那个sheet页写入数据，如果不指定，，默认写在第一个sheet页，默认sheet名：0

源码解释：所有重载的方法可归为一个方法，接收sheetNo(第几个sheet（Integer）)，sheetName(sheet页名称(String))，返回ExcelWriterSheetBuilder

  /*选中第一个sheet页写操作 sheet 页的值为 0*/public ExcelWriterSheetBuilder sheet() {return sheet(null, null);}/*选中 第一个的 sheet页sheet 页的名字 为 sheetNo*/  public ExcelWriterSheetBuilder sheet(Integer sheetNo) {return sheet(sheetNo, null);}/*选中第一个的 sheet页sheet 页的名字 为 sheetName*/  public ExcelWriterSheetBuilder sheet(String sheetName) {return sheet(null, sheetName);}/*选中第一个 sheet页sheet 页的名字 为 sheetNo 或者 sheetName*/public ExcelWriterSheetBuilder sheet(Integer sheetNo, String sheetName) {ExcelWriter excelWriter = build();ExcelWriterSheetBuilder excelWriterSheetBuilder = new ExcelWriterSheetBuilder(excelWriter);if (sheetNo != null) {excelWriterSheetBuilder.sheetNo(sheetNo);}if (sheetName != null) {excelWriterSheetBuilder.sheetName(sheetName);}return excelWriterSheetBuilder;

doWrite方法

源码如下：

public void doWrite(List data) {if (this.excelWriter == null) {throw new ExcelGenerateException("Must use 'EasyExcelFactory.write().sheet()' to call this method");} else {this.excelWriter.write(data, this.build());this.excelWriter.finish();}}

如上可见，doWrite方法只是简单判断了一下当前ExcelWriterSheetBuilder类是否为空，然后调用了write方法，再关闭excelWriter

我们在深入看一下write方法

public ExcelWriter write(List data, WriteSheet writeSheet) {return this.write(data, (WriteSheet)writeSheet, (WriteTable)null);
}public ExcelWriter write(List data, WriteSheet writeSheet, WriteTable writeTable) {this.excelBuilder.addContent(data, writeSheet, writeTable);return this;
}

本质上这两个方法属于一个方法，都是接收三个参数，返回ExcelWriter对象

List data: 要写入的数据
WriteSheet writeSheet: doWrite方法返回ExcelWriterSheetBuilder中的一个属性，存放了sheet信息
writeTable: 存放table信息，暂不讨论

 /** @deprecated */
@Deprecated
public ExcelWriter write(List data, Sheet sheet) {return this.write(data, (Sheet)sheet, (Table)null);
}/** @deprecated */
@Deprecated
public ExcelWriter write(List data, Sheet sheet, Table table) {WriteSheet writeSheet = null;if (sheet != null) {writeSheet = new WriteSheet();writeSheet.setSheetNo(sheet.getSheetNo() - 1);writeSheet.setSheetName(sheet.getSheetName());writeSheet.setClazz(sheet.getClazz());writeSheet.setHead(sheet.getHead());writeSheet.setTableStyle(sheet.getTableStyle());writeSheet.setRelativeHeadRowIndex(sheet.getStartRow());writeSheet.setColumnWidthMap(sheet.getColumnWidthMap());}return this.write(data, writeSheet, writeTable);
}

已过时方法，本质如上,根据return语句看，还是调用以上方法，

接着看一下addContent

    public void addContent(List data, WriteSheet writeSheet) {this.addContent(data, writeSheet, (WriteTable)null);}public void addContent(List data, WriteSheet writeSheet, WriteTable writeTable) {try {this.context.currentSheet(writeSheet, WriteTypeEnum.ADD);this.context.currentTable(writeTable);if (this.excelWriteAddExecutor == null) {this.excelWriteAddExecutor = new ExcelWriteAddExecutor(this.context);}this.excelWriteAddExecutor.add(data);} catch (RuntimeException var5) {this.finishOnException();throw var5;} catch (Throwable var6) {this.finishOnException();throw new ExcelGenerateException(var6);}}

addContent接收了Excel原始数据，通过excelWriteAddExecutor.add写入，具体写入过程可看此方法

表头操作

属性注解

@Data
public class Student implements Serializable {@ExcelProperty(value = {"学生编号"},order = 10)@NumberFormat("#,###")private Integer id;@ExcelProperty(value = {"学生姓名"},order = 2)private String name;@ExcelProperty(value = {"学生薪水"},order = 1)@ExcelIgnoreprivate Double salary;@ExcelProperty(value = {"学生生日"},order = 11)@DateTimeFormat("yyyy-mm-dd")private Date birthday;
}

如上所见，我们在每个属性上加入了@ExcelProperty注解，表示当前属性是一个excel字段，easyexcel采用了注解的方式定义excel 表头字段，给我们开发带来了极大的便利。

ExcelProperty index 指定写到第几列，默认根据成员变量排序。value指定写入的名称，默认成员变量的名字，多个value可以参照快速开始中的复杂头
ExcelIgnore 默认所有字段都会写入excel，这个注解会忽略这个字段
DateTimeFormat 日期转换，将Date写到excel会调用这个注解。里面的value参照java.text.SimpleDateFormat
NumberFormat 数字转换，用Number写excel会调用这个注解。里面的value参照java.text.DecimalFormat
ExcelIgnoreUnannotated 默认不加ExcelProperty 的注解的都会参与读写，加了不会参与

还有其他注解，地址都在：com.alibaba.excel.annotation