通过 Excel 来认识神器 Apache POI
1、POI是什么
Apache POI - the Java API for Microsoft Documents，顾名思义，Apache的三方包，用来操作微软office文档的，多数时候用来操作excel，所以这里就以excel方面来说明。
<dependency>
<groupId>org.apache.poi</groupId>
<artifactId>poi</artifactId>
<version>3.9</version>
</dependency>
<dependency>
<groupId>org.apache.poi</groupId>
<artifactId>poi-ooxml</artifactId>
<version>3.9</version>
</dependency>
POI的组件列表中，针对excel的主要是HSSF和XSSF组件，前者针对97-2007的通用版excel，即后缀xls；后者针对2007或更高版的excel，即后缀xlsx。
官方概要如下：
HSSF is the POI Project's pure Java implementation of the Excel '97(-2007) file format.
XSSF is the POI Project's pure Java implementation of the Excel 2007 OOXML (.xlsx) file format.
2、POI核心类
面向对象面向对象，既然如此，自然去找找一些能表示excel中内容的类。
2.1 工作簿 Workbook
创建或维护Excel工作簿的所有类的超接口，Workbook，属于org.apache.poi.ss.usermodel包。
其下有两个实现类：
-
HSSFWorkbook : 有读取.xls 格式和写入Microsoft Excel文件的方法。它与微软Office97-2003版本兼容 -
XSSFWorkbook : 有读写Microsoft Excel和OpenOffice的XML文件的格式.xls或.xlsx的方法。它与MS-Office版本2007或更高版本兼容
所以在针对不同版本的excel时，需要对应以上使用不同的Workbook。构造函数中，常用的：
HSSFWorkbook
HSSFWorkbook()
HSSFWorkbook(java.io.InputStream s)
XSSFWorkbook
XSSFWorkbook()
XSSFWorkbook(java.io.File file)
XSSFWorkbook(java.io.InputStream is)
2.2 标签页 Sheet
HSSFSheet 和 XSSFSheet 都是Sheet接口的实现类，Sheet可以使用Workbook的两个方法获得：
workbook.createSheet();
workbook.createSheet(String sheetName);
2.3 行 Row
同理，Row是 HSSFRow 和 XSSFRow 的接口，通过Sheet获取：
sheet.createRow(int rownum);
2.4 单元格 Cell
同理，Cell是 HSSFCell 和 XSSFCell 的接口，通过Row获取：
row.createCell(int column);
row.createCell(int column, int type);
3、创建和读取
其实如果能理解面向对象，就很简单了，另外包括字体，公式，超链接等，都有对应的封装类，此处只提出了核心的几个，需要了解更多的需要自行展开。
例子的话，直接从别人教程里摘出来吧，另，读取的workbook，可以debug瞅瞅内容。关注公从号Java技术栈，回复：工具，可以获取更多工具系列干货。
3.1 创建空白工作簿
import java.io.*;
import org.apache.poi.xssf.usermodel.*;
public class CreateWorkBook
{
public static void main(String[] args)throws Exception
{
XSSFWorkbook workbook = new XSSFWorkbook();
FileOutputStream out = new FileOutputStream(
new File("createworkbook.xlsx"));
workbook.write(out);
out.close();
System.out.println("
createworkbook.xlsx written successfully");
}
}
3.2 打开现有的工作簿
import java.io.*;
import org.apache.poi.xssf.usermodel.*;
public class OpenWorkBook
{
public static void main(String args[])throws Exception
{
File file = new File("openworkbook.xlsx");
FileInputStream fIP = new FileInputStream(file);
XSSFWorkbook workbook = new XSSFWorkbook(fIP);
if(file.isFile() && file.exists())
{
System.out.println(
"openworkbook.xlsx file open successfully.");
}
else
{
System.out.println(
"Error to open openworkbook.xlsx file.");
}
}
}
3.3、任意对象List转至为Excel文档
可用注解定义标签名和列名，写了个方法，可以将某个类的List转换为对应的Excel文档，列名如果在不使用注解的情况下默认为属性名：
类：
@Excel(name = "学生标签页")
public class Student {
@Excel(name = "姓名")
private String name;
private boolean male;
@Excel(name = "身高")
private int height;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public boolean isMale() {
return male;
}
public void setMale(boolean male) {
this.male = male;
}
public int getHeight() {
return height;
}
public void setHeight(int height) {
this.height = height;
}
}
测试方法：
public static void main(String[] args) {
List<Student> list = new ArrayList<Student>();
Student student1 = new Student();
student1.setName("小红");
student1.setMale(false);
student1.setHeight(167);
Student student2 = new Student();
student2.setName("小明");
student2.setMale(true);
student2.setHeight(185);
list.add(student1);
list.add(student2);
File file = new File("C:/Users/Dulk/Desktop/1314.xls");
createExcel(list, file);
}
输出结果：
注解：
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
@Retention(RetentionPolicy.RUNTIME)
public @interface Excel {
public String name() default "";
}
方法：
import org.apache.log4j.Logger;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
public class ExcelUtil {
private static Logger log = Logger.getLogger(ExcelUtil.class);
public static Workbook gainWorkbook(File file) throws ExcelException {
if (!isExcel(file)) {
throw new ExcelException("文件不是Excel类型");
}
if (!file.exists()) {
try {
OutputStream os = new FileOutputStream(file);
Workbook workbook = isOlderEdition(file) ? new HSSFWorkbook() : new XSSFWorkbook();
workbook.write(os);
log.debug("文件不存在，新建该Excel文件");
os.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
try {
InputStream is = new FileInputStream(file);
return isOlderEdition(file) ? new HSSFWorkbook(is) : new XSSFWorkbook(is);
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
private static boolean isOlderEdition(File file) {
return file.getName().matches(".+\\.(?i)xls");
}
private static boolean isExcel(File file) {
String fileName = file.getName();
String regXls = ".+\\.(?i)xls";
String regXlsx = ".+\\.(?i)xlsx";
return fileName.matches(regXls) || fileName.matches(regXlsx);
}
public static <E> Workbook createExcel(List<E> list, File file) {
String sheetName = "default";
if (list.size() == 0) {
return null;
}
Workbook workbook = null;
try {
Class clazz = list.get(0).getClass();
Field[] fields = clazz.getDeclaredFields();
if (clazz.isAnnotationPresent(Excel.class)) {
Excel excel = (Excel) clazz.getAnnotation(Excel.class);
sheetName = excel.name();
}
workbook = gainWorkbook(file);
Sheet sheet = workbook.createSheet(sheetName);
Row line = sheet.createRow(0);
for (int k = 0; k < fields.length; k++) {
Cell cell = line.createCell(k);
String columnName = fields[k].getName();
if (fields[k].isAnnotationPresent(Excel.class)) {
Excel excel = fields[k].getAnnotation(Excel.class);
columnName = excel.name();
}
cell.setCellValue(columnName);
}
for (int i = 1; i <= list.size(); i++) {
Row row = sheet.createRow(i);
for (int j = 1; j <= fields.length; j++) {
Cell cell = row.createCell(j - 1);
String fieldName = fields[j - 1].getName();
String fieldFirstLetterUpper = fieldName.substring(0, 1).toUpperCase();
String prefix = "get";
if ("boolean".equals(fields[j - 1].getType().getName())) {
prefix = "is";
}
String methodName = prefix + fieldFirstLetterUpper + fieldName.substring(1);
Method method = clazz.getMethod(methodName);
cell.setCellValue(String.valueOf(method.invoke(list.get(i - 1))));
}
}
log.debug("List读入完毕");
OutputStream os = new FileOutputStream(file);
workbook.write(os);
os.close();
} catch (ExcelException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return workbook;
}
}往期推荐
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