Detailed example of how Java generates excel through apache poi

<!-- https://mvnrepository.com/artifact/org.apache.poi/poi-ooxml -->
<dependency>
 <groupId>org.apache.poi</groupId>
 <artifactId>poi-ooxml</artifactId>
 <version>3.15</version>
</dependency>

//创建excel文档
XSSFWorkbook workbook = new XSSFWorkbook();
//创建sheet
XSSFSheet sheet = workbook.createSheet("sheetName");

int rownum=0;
//创建首行
XSSFRow firstrow = sheet.createRow(rownum++);
int cellnum = 0;
//把保存在titles中的各个列名，分别在row中创建cell
for(String key : titles){
 XSSFCell cell = firstrow.createCell(cellnum++);
 cell.setCellValue(key);
}


//下面可以继续创建行

//把excel写到要写的outputStream中
workbook.write(output);
//最后关闭
workbook.close();

package me.paul.excelDemo;

import java.io.IOException;
import java.io.OutputStream;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.poi.xssf.usermodel.XSSFCell;
import org.apache.poi.xssf.usermodel.XSSFRow;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;


public class ExcelUtil {
 
 public <T> void getExcel(List<T> list,Class<T> c,OutputStream output) throws IOException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{
 Map<String,Method> methodMap = new LinkedHashMap<>(); 
 Method[] methods = c.getDeclaredMethods();
 for(int i=0;i<methods.length;i++){
  Method method = methods[i];
  String name = method.getName();
  Pattern pattern = Pattern.compile("get(.*)");
  Matcher matcher = null;
  if((matcher = pattern.matcher(name)).matches()){
  name = matcher.group(1);
  char ch = name.charAt(0);
  char newch = (char) (ch + 32); 
  name = name.replace(ch,newch);
  methodMap.put(name, method);
  }
 }
 
 XSSFWorkbook workbook = new XSSFWorkbook();
 XSSFSheet sheet = workbook.createSheet(c.getCanonicalName());
 int rownum=0;
 XSSFRow firstrow = sheet.createRow(rownum++);
 int cellnum = 0;
 for(String key : methodMap.keySet()){
  XSSFCell cell = firstrow.createCell(cellnum++);
  cell.setCellValue(key);
 }
 
 for(T t : list){
  XSSFRow row = sheet.createRow(rownum++);
  cellnum = 0;
  for(String key:methodMap.keySet()){
  Method method = methodMap.get(key);
                //设置可访问，之前不知道这方法，所以关于反射那篇文章有错误，见谅见谅
                method.setAccessible(true);
  Object obj = method.invoke(t);
  XSSFCell cell = row.createCell(cellnum++);
  cell.setCellValue(obj== null ? "":obj.toString());
  }
  
 }
 workbook.write(output);
 workbook.close();
 } 
}

package me.paul.excelDemo;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.lang.reflect.InvocationTargetException;
import java.util.ArrayList;
import java.util.List;

public class App {
 public static void main(String[] args) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException, IOException {
 List<User> list = new ArrayList<>();
 User u = new User();
 u.setId(1);
 u.setName("Paul");
 u.setAge(18);
 list.add(u);
 u = new User();
 u.setId(2);
 u.setName("Johnson");
 u.setAge(20);
 list.add(u);
 u = new User();
 u.setId(3);
 u.setName("David");
 u.setAge(22);
 list.add(u);
 OutputStream output = new FileOutputStream("/home/paul/user.xlsx");
 new ExcelUtil().getExcel(list, User.class,output);
 output.close();
 }
}