1、發郵件，得先將郵件開啟smtp，才可以發郵件

思路：先將資料庫的資料下載儲存到excel中，然後將附件的形式傳送，其中利用到資料流

package com.example;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Iterator;
import java.util.List;

import javax.mail.internet.MimeMessage;

import org.apache.poi.hssf.usermodel.HSSFCell;
import org.apache.poi.hssf.usermodel.HSSFFont;
import org.apache.poi.hssf.usermodel.HSSFRichTextString;
import org.apache.poi.hssf.usermodel.HSSFRow;
import org.apache.poi.hssf.usermodel.HSSFSheet;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.hssf.util.HSSFColor;
import org.jboss.logging.Logger;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.core.io.FileSystemResource;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.mail.javamail.MimeMessageHelper;
import org.springframework.scheduling.annotation.EnableScheduling;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.transaction.annotation.EnableTransactionManagement;

import com.example.entity.SelectPhoneAndTid;
import com.example.service.SelectPhoneAndTidService;
@SpringBootApplication
//開啟事務
@EnableTransactionManagement
//掃包
@MapperScan("com.example.dao.SelectPhoneAndTidDao")

@EnableScheduling 
public class PoiExcellApplication {
	@Autowired
    private JavaMailSender mailSender; //自動注入的Bean
	@Autowired
	private SelectPhoneAndTidService stService;
    @Value("${spring.mail.username}")
    private String Sender; //讀取配置檔案中的引數
     
	@Scheduled(cron = "00 00 09 * * ?") 
	public void contextLoads() throws IOException {
        String[] headers = { "手機號碼", "訂單編號"};//匯出的Excel頭部
        List<SelectPhoneAndTid> dataset = stService.findAll();//查詢出來的資料
        // 宣告一個工作薄
        HSSFWorkbook workbook = new HSSFWorkbook();
        // 生成一個表格
        HSSFSheet sheet = workbook.createSheet();
        // 設定表格預設列寬度為20個位元組
        sheet.setDefaultColumnWidth((short) 20);
        HSSFRow row = sheet.createRow(0);
        for (short i = 0; i < headers.length; i++) {
            HSSFCell cell = row.createCell(i);
            HSSFRichTextString text = new HSSFRichTextString(headers[i]);
            cell.setCellValue(text);
        }
        //遍歷集合資料，產生資料行
        Iterator<SelectPhoneAndTid> it = dataset.iterator();
        int index = 0;
        while (it.hasNext()) {
            index++;
            row = sheet.createRow(index);
            SelectPhoneAndTid t = (SelectPhoneAndTid) it.next();
            //利用反射，根據javabean屬性的先後順序，動態呼叫getXxx()方法得到屬性值
            Field[] fields = t.getClass().getDeclaredFields();
            for (short i = 0; i < fields.length; i++) {
                HSSFCell cell = row.createCell(i);
                Field field = fields[i];
                String fieldName = field.getName();
                String getMethodName = "get"
                        + fieldName.substring(0, 1).toUpperCase()
                        + fieldName.substring(1);
                try {
                    Class tCls = t.getClass();
                    Method getMethod = tCls.getMethod(getMethodName,new Class[]{});
                    Object value = getMethod.invoke(t, new Object[]{});
                    String textValue = null;
                    if (value instanceof Date)
                    {
                        Date date = (Date) value;
                        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                        textValue = sdf.format(date);
                    }else{
                        //其它資料型別都當作字串簡單處理
                        textValue = value.toString();
                    }       
	                    HSSFRichTextString richString = new HSSFRichTextString(textValue);
	                    HSSFFont font3 = workbook.createFont();
	                    font3.setColor(HSSFColor.BLACK.index);//定義Excel資料顏色
	                    richString.applyFont(font3);
	                    cell.setCellValue(richString);
                } catch (SecurityException e) {
                    e.printStackTrace();
                } catch (NoSuchMethodException e) {
                    e.printStackTrace();
                } catch (IllegalArgumentException e) {
                    e.printStackTrace();
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                } catch (InvocationTargetException e) {
                    e.printStackTrace();
                }
            }
        }
        
      Date d=new Date();
      SimpleDateFormat f=new SimpleDateFormat("yyyy-MM-dd");
      String fn= f.format(d);
      //檔名稱防止檔名含有中文亂碼
      String filedisplay =fn+".xls";
      filedisplay = new String( filedisplay.getBytes("gb2312"), "ISO8859-1" );
      //檔案匯入的地方
       FileOutputStream fileOut = null;    
        try{                
            fileOut = new FileOutputStream("D:\\每天傳送的表格資料\\"+filedisplay);    
            workbook.write(fileOut);     
        }catch(Exception e){    
            e.printStackTrace();    
        }finally{    
            if(fileOut != null){    
                try {    
                    fileOut.close();    
                } catch (IOException e) {       
                    e.printStackTrace();    
                }    
            } 
            
        //發郵件
   		 MimeMessage message = null;
   	        try {
   	            message = mailSender.createMimeMessage();
   	            MimeMessageHelper helper = new MimeMessageHelper(message, true);
   	         
	   	       helper.setTo("傳送的地址");
	   	       
   	            helper.addTo("增加的地址");
   	           	helper.setSubject("主題：帶附件的郵件");
   	           	helper.setText("帶附件的郵件內容");
   	            //注意專案路徑問題，自動補用專案路徑
   	            FileSystemResource file = new FileSystemResource(new File("D:\\每天傳送的表格資料\\"+fn+".xls"));
   	            //加入郵件
   	            helper.addAttachment(fn+".xls", file);
   	        } catch (Exception e){
   	            e.printStackTrace();
   	        }
   	        mailSender.send(message);
        }   
		
}
	
	public static void main(String[] args) {
		SpringApplication.run(PoiExcellApplication.class, args);
	}
}