求助！JSP截取字符串问题，急！！！

Question

用substring之前先判断lianxidizhi是否等于null
如果是null再用substring就会抛出NullPointerException的了

Answer 1

lianxidizhi==null?"":lianxidizhi.substring(0, 6)

Answer 2

if(!lianxidizhi==""||lianxidizhi==null)
lianxidizhi.substring(0, 6)

Answer 3

if(lianxidizhi!=null&&!lianxidizhi==""){
out.print(lianxidizhi.substring(0, 6));
}

Answer 4

if(lianxidizhi==""||lianxidizhi==null){
lianxidizhi.substring(0, 6);
}

Answer 5

if(lianxidizhi!=null)
   if(lianxidizhi.length()>=10)
       lianxidizhi=lianxidizhi.substring(0,6);