Customize a validator--------------------------when the user registers, whether the username conforms to the rules and the time already exists in the database checksum

Instance:

<!--custom Check form-->$.validator.addmethod ("Checkusername",      //Check rule name, similar to Requiredfunction (Value,element, params) {//define a flag flag to mark whether the user name already exists var flag = False;$.ajax ({"Async": false,//must be synchronized here, because asynchronous processing, first executes the return statement, resulting in the inability to effectively return                "url": "${pagecontext.request.contextpath}/checkusername", "data": {"username": Value}, "type": " POST "," DataType ":" JSON "," Success ": function (data) {flag = Data.isexist;  Indicates whether the user name already exists in the database});//false indicates that the validator does not pass, that is, the user name is already in the database return!flag;});    Where: Value: Indicates the label entered for the check.        /element: Indicates the label in which the check is located   //        params: The parameter that represents the check rule

　　

　　

Customize a validator--------------------------when the user registers, whether the username conforms to the rules and the time already exists in the database checksum