java怎么从数据库导出数据 java从数据库导出csv

1、首先需要准备一个jar包   javacsv.jar

2、编写一个将数据写入csv的方法

/**
	 * 写入csv
	 * @param request
	 * @param rootPath
	 * @param title
	 * @param headers
	 * @param dataset
	 * @param out
	 */
public void exportCSV(HttpServletRequest request,String rootPath, String title, String[] headers,List<LinkedHashMap<String, Object>> dataset, OutputStream out) {
		try {
			System.out.println(rootPath);
			CsvWriter csvWriter = new CsvWriter(rootPath,',', Charset.forName("UTF-8"));
			//写入表头信息
			csvWriter.writeRecord(headers);
		    //写入内容信息
			for(int k=0;k<dataset.size();k++){
				curcount++;
				LinkedHashMap<String, Object> infos=dataset.get(k);
				String agent_id=infos.get("agent_id").toString();
				String extension=infos.get("extension").toString();
				String starttime=infos.get("starttime").toString();
				String endtime=infos.get("endtime").toString();
				String info=infos.get("info").toString();	
				csvWriter.write(agent_id);
				csvWriter.write(extension);
				csvWriter.write(starttime);
				csvWriter.write(endtime);
				csvWriter.write(info);
				csvWriter.endRecord();
				
				//导出的进度条信息
				 double dPercent=(double)curcount/totalCount;   //将计算出来的数转换成double
		         int  percent=(int)(dPercent*100);               //再乘上100取整
		         request.getSession().setAttribute("curCount", curcount);
		         request.getSession().setAttribute("percent", percent);    //比如这里是50
		         request.getSession().setAttribute("percentText",percent+"%");//这里是50%	
			}
			//关闭写入的流   
			csvWriter.close();
			File fileLoad = new File(rootPath);  
			FileInputStream in = new java.io.FileInputStream(fileLoad);
		   //每次写入10240个字节
			byte[] b = new byte[10240];
			int n;  
			while ((n = in.read(b)) != -1) {  
		  	 out.write(b, 0, n); //每次写入out1024字节 
			}  
		  	 in.close();  
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}	
	}

3、设置导出的文件的格式和其他的必要信息

/***
	 * 导出成csv文件
	 * @param request
	 * @param response
	 * @param title
	 * @param headers
	 * @param allList
	 * @return
	 */
	public synchronized String mapOutToCSV(HttpServletRequest request,
			HttpServletResponse response, String title, String[] headers,
			List<LinkedHashMap<String, Object>> allList){
		totalCount=allList.size();
		int len = headers.length;
		trace.info("@header length=" + len + " title:" + title);
		OutputStream out = null;// 创建一个输出流对象
		try {
			/* 截取掉表名中多余的部分 */
			title = title.replaceAll(":", "-");
			title = title.replaceAll("（", "(");
			title = title.replaceAll("）", ")");
			String subTitle = title;
			String filename = new String((subTitle).getBytes("UTF-8"),"iso8859-1");
			trace.info("@filename:=" + filename);
			out = response.getOutputStream();//
			response.setHeader("Content-disposition", "attachment; filename="+ filename + ".csv");// filename是下载的xls的名，建议最好用英文
			response.setContentType("application/csv;charset=UTF-8");// 设置类型
			response.setHeader("Pragma", "No-cache");// 设置头
			response.setHeader("Cache-Control", "no-cache");// 设置头
			response.setDateHeader("Expires", 0);// 设置日期头
			String rootPath = request.getSession().getServletContext().getRealPath("/")+ filename + ".csv";
			exportCSV(request,rootPath, title, headers, allList, out);
			out.flush();
		} catch (IOException e) {
			trace.error("OutToCSV OutputStream " + e.getMessage());
		} finally {
			try {
				if (out != null) {
					out.close();
				}
			} catch (IOException e) {
				trace.error("OutToCSV OutputStream close " + e.getMessage());
			}
		}
				return null;
	}

4、后台调用该方法即可实现导出成csv文件

@RequestMapping(value="/excelData.html",method=RequestMethod.GET,params={"fromTime","toTime"})
	public Object excelDataRate(HttpServletRequest request,HttpServletResponse response,String fromTime,String toTime){
		request.getSession().removeAttribute("totalCount");
        request.getSession().removeAttribute("curCount");
        request.getSession().removeAttribute("percent");
        request.getSession().removeAttribute("percentText");
		ArrayList<LinkedHashMap<String, Object>> DataListALL=trans.selectDataList(fromTime, toTime);
		String[] headers = {" 员工编号  ", "   分机号   ", " 开始时间 ", "结束时间", "对话信息", };
		ExportExcelUtil ex = new ExportExcelUtil();
		//return ex.mapOutToExcel(request, response, "语音转文本的信息数据", headers,DataListALL);
		return  ex.mapOutToCSV(request, response,"语音转文本的信息数据"+fromTime+"至"+toTime, headers, DataListALL);
	}

5、前台调用，只要两行代码集合实现

  在函数中写入下面两句代码

var url="${pageContext.request.contextPath}/excelData.html?fromTime="+encodeURI(starttime)+"&toTime="+encodeURI(endtime);
window.location.href=url;

该类方法中还存在进度条信息，导出时存在进度条