String 转 Date
String classCode = RequestHandler.getString(request, "classCode");SimpleDateFormat sdf = new SimpleDateFormat("yyyy-mm-dd hh:mm:ss");DicClassInfo classInfo=new DicClassInfo();classInfo.setStartDate(sdf.parse(startDate)); int型除法保留两位小数/求百分比
int openCount = temp.getIsOpenCount();int passCount = temp.getIsPassCount();double k = (double)passCount/openCount*100;java.math.BigDecimal big = new java.math.BigDecimal(k);String l =big.setScale(2,java.math.BigDecimal.ROUND_HALF_UP).doubleValue() +"%";
float保留两位小数
//1float f = 34.232323; BigDecimal b = new BigDecimal(f); float f1 = b.setScale(2, BigDecimal.ROUND_HALF_UP).floatValue(); // b.setScale(2, BigDecimal.ROUND_HALF_UP) 表明四舍五入，保留两位小数 //2float scale = 34.236323; DecimalFormat fnum = new DecimalFormat("##0.00"); String dd=fnum.format(scale); System.out.println(dd);//3float a = 123.2334f; float b = (float)(Math.round(a*100))/100; BigDecimal保留两位小数
//金额保留小数后两位BigDecimal b = invoiceTemp.getInvoicePrice();BigDecimal setScale = b.setScale(2,BigDecimal.ROUND_DOWN);invoiceTemp.setInvoicePrice(setScale);
参数定义
ROUND_CEILING 向正无穷方向舍入
ROUND_DOWN 向零方向舍入 ROUND_FLOOR 向负无穷方向舍入 ROUND_HALF_DOWN 向（距离）最近的一边舍入，除非两边（的距离）是相等,如果是这样，向下舍入, 例如1.55 保留一位小数结果为1.5 ROUND_HALF_EVEN 向（距离）最近的一边舍入，除非两边（的距离）是相等,如果是这样，如果保留位数是奇数，使用ROUND_HALF_UP ，如果是偶数，使用ROUND_HALF_DOWN ROUND_HALF_UP 向（距离）最近的一边舍入，除非两边（的距离）是相等,如果是这样，向上舍入, 1.55保留一位小数结果为1.6 ROUND_UNNECESSARY 计算结果是精确的，不需要舍入模式 ROUND_UP 向远离0的方向舍入
Action文件mapping.findForward()动态传参至Struts-config.xml
//后台方法return mapping.findForward(outSystemSign);//配置文件无需判断，直接接收，直接写明映射内容即可
isBlank、isEmpty、isNull
org.apache.commons.lang.StringUtils类提供了String的常用操作,最常用判空如下
- StringUtils.isEmpty(String str)
//判断某字符串是否为空，标准是 str==null 或 str.length()==0System.out.println(StringUtils.isEmpty(null)); //trueSystem.out.println(StringUtils.isEmpty("")); //trueSystem.out.println(StringUtils.isEmpty(" ")); //falseSystem.out.println(StringUtils.isEmpty("dd")); //false - StringUtils.isNotEmpty(String str) 等价于 !isEmpty(String str),判断是否不为空也不为null，在要替换字段为空串时，应使用isNotNull，isNotEmpty会自动跳过
- StringUtils.isBlank(String str)，StringUtils.isNotBlank(String str) 等价于 !isBlank(String str)
//判断某字符串是否为空或长度为0或由空白符(whitespace) 构成System.out.println(StringUtils.isBlank(null)); //trueSystem.out.println(StringUtils.isBlank("")); //trueSystem.out.println(StringUtils.isBlank(" ")); //trueSystem.out.println(StringUtils.isBlank("dd")); //false 时间段控制（00:00:00—23:59:59）
if(null!=startDate){ int len = startDate.length(); switch(len){ case(10):startDate = startDate + " 00:00:00.000";break; case(19):startDate = startDate + ".000";break; default:if(len>10){startDate = startDate.substring(0,10)+"00:00:00.000";}break; }}if(null!=endDate){ int len = endDate.length(); switch(len){ case(10):endDate = endDate + " 23:59:59.999";break; case(19):startDate = startDate + ".999";break; default:if(len>10){startDate = startDate.substring(0,10)+"23:59:59.999";}break; }} 计算时间差
String date = "2010-01-01 11:11:11";SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); String nowDate = df.format(new Date());Date d1 = df.parse(date);Date d2 = df.parse(nowDate);long between = (d2.getTime() - d1.getTime())/1000; //时间差（秒） 获取指定时间
//当前月第一天Calendar c = Calendar.getInstance();c.setTime(new Date());c.set(5, 1); Date startMonthDate =c.getTime()；String startMonthStr = dateToString(startMonthDate , "yyyy-MM-dd 00:00:00");//当前月最后一天Calendar calendar = Calendar.getInstance();calendar.setTime(startMonthDate );calendar.add(2, n);Date endMonthDate=calendar .getTime()；String endMonthStr = dateToString(endMonthDate, "yyyy-MM-dd 00:00:00");//七天前Calendar calendar = Calendar.getInstance();calendar.set(Calendar.DAY_OF_YEAR, calendar.get(Calendar.DAY_OF_YEAR) - 7);Date earlySevenDate = calendar.getTime();String earlySevenStr = dateToString(earlySevenDate, "yyyy-MM-dd 00:00:00");//当天String todayStr = dateToString(new Date(), "yyyy-MM-dd 00:00:00");//Date date, int n date时间加n天Calendar calendar = Calendar.getInstance();calendar.setTime(date);calendar.add(5, n);Date nDayLaterDate = calendar.getTime(); String earlySevenStr = dateToString(nDayLaterDate, "yyyy-MM-dd 00:00:00");//Date date, int n date时间加n月Calendar calendar = Calendar.getInstance();calendar.setTime(date);calendar.add(2, n);Date nMonthLaterDate = calendar.getTime();String earlySevenStr = dateToString(nMonthLaterDate, "yyyy-MM-dd 00:00:00");public static String dateToString(Date date, String pattern) { if (date != null) { SimpleDateFormat sdf = new SimpleDateFormat(pattern); return sdf.format(date); } else { return ""; }}//Calendar的add()方法：1是对年份操作，2是对月份操作，3是对星期操作，5是对日期操作，11是对小时操作，12是对分钟操作，13是对秒操作，14是对毫秒操作。 String数组、List转换
// List转String数组Listlist = new ArrayList (); list.add("a1"); list.add("a2"); String[] toBeStored = list.toArray(new String[list.size()]); for(String s : toBeStored) { System.out.println(s); } //String数组转ListString[] arr = new String[] {"1", "2"}; List list = Arrays.asList(arr);
excel导出合并单元格（行）、设置样式
<%@page import="org.apache.poi.hssf.util.Region"%><%@page import="org.apache.poi.hssf.usermodel.HSSFFont"%><%@page import="org.apache.poi.hssf.util.HSSFColor"%> HSSFCellStyle cellStyle = wb.createCellStyle();//新样式//居中cellStyle.setAlignment(HSSFCellStyle.ALIGN_CENTER); //居中HSSFFont font=wb.createFont();font.setColor(HSSFColor.RED.index);//字体颜色font.setFontHeightInPoints((short)12);font.setBoldweight(HSSFFont.BOLDWEIGHT_BOLD);//字体增粗cellStyle.setFont(font);//把字体应用到当前的样式cell.setCellStyle(cellStyle);//合并第（0，0）单元格到第（0,13）单元格sheet.addMergedRegion(new Region(0, (short)0, 0, (short)13));if(0 != total){ cell.setCellValue("支付金额合计 : "+total+"元");} excel动态合并单元格（列）
short num = 1; //列String s = "";//sheet.getLastRowNum()获取总行数for (int k = 1; k <= sheet.getLastRowNum(); k++) { HSSFRow rows = sheet.getRow(k); HSSFCell cells = rows.getCell((short)2); if (cells.getStringCellValue().equals(s)) { sheet.addMergedRegion(new Region(num,(short)2,k,(short)2)); HSSFRow rowsV = sheet.getRow(k); HSSFCell cellsV = rows.getCell((short)2); cellsV.setCellStyle(style); } else { num =(short) k;} s = cells.getStringCellValue();}