PreparedStatement like 的用法

String expr = "select * from table where url like ?";
pstmt = con.prepareStatement(expr);
String a="a";
pstmt.setString(1, "%"+a+"%");
pstmt.execute();

这样写 PreparedStatement  会默认生成sql语句： select * from table where url like '%http%' 

不要这样写

String expr = "select * from table where url like %?%";

String expr = "select * from table where url like %?%";

 也不要这样写

pstmt = con.prepareStatement(expr);
String a="%a%";
pstmt.setString(1, a);
pstmt.execute();