常用小功能

JSON字符串解析

用例：JSONArray jsonArray = JSONArray.parseArray(Capacity);

List<Capacity> list = new ArrayList<Capacity>();
for(int i =0;i < jsonArray.size();i++){
list.add(jsonArray.getObject(i,Capacity.class));
}

后台跨域

...HttpServletResponse response) {
response.setHeader("Access-Control-Allow-Origin", "*");

登录

String url = request.getRequestURL().toString();//获得客户端发送请求的完整链接
int a = url.indexOf("//")+2;
int b= url.indexOf(":",7);
String ip= url.substring(a,b);
StringBuffer buf = new StringBuffer();
String requestURI = request.getRequestURI();
String serverName = requestURI.split("/")[1];
String protect = requestURI.split("/")[2]; 
buf.append(ip)
.append(":")
.append(request.getLocalPort())
.append(",")
.append(serverName)
.append(",")
.append(protect)
.append(",")
.append(request.getParameter("access_token"))
//.append(tt.substring(17,53))
.append(",")
.append(request.getSession().getId())
.append(",")
.append(stu.getId());
//登录时将个人信息保存在session
session.setAttribute("id"+stu.getId(), stu.getId());
session.getAttribute("id"+stu.getId());

随机生成字母+数字的指定长度字符串组合

String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
Random random = new Random();
for (int i = 0; i < 4; i++) {
int num = random.nextInt(62);
stringBuffer.append(str.charAt(num));
}

指定格式化数字的位数

// 创建一个数值格式化对象
NumberFormat numberFormat = NumberFormat.getInstance();
// 设置精确到小数点后2位
numberFormat.setMaximumFractionDigits(2);

//指定格式化

numberFormat.format();