Java. Lang. numberformatexception: NULL

encoding JAVA. lang. numberformatexception: NULL, at java. lang. integer. parseint (integer. java: 415) at java. lang. integer. valueof (integer. java: 553) . at the beginning, I thought that my type conversion was incorrect. It turns out that it is not careful enough. When passing the URL value, you forget to pass the parameter or pass the error. In this case, the obtained value is null. For example, the URL is http ://...... & State = 1, the passed parameter is state = 1, this parameter must be int state = integer. parseint (request. getparameter ("state") . in this way, no error is reported, but if you forget to pass the parameter state = 1 in the address bar, JAVA. lang. numberformatexception: NULL .............

SO JAVA. lang. the numberformatexception error is not necessarily type conversion error , it may also be because the parameter cannot be obtained errors