EL表达式关系演算 备案

el表达式的取值默认顺序:?pageScope? requestScope? sessionScope? applicationScope
???
结构，采用.导航，也称为存取器?? ${user.name}? ${user.class.name}
????????????????????? 输出map?? ${mapValue.key1}
???????????????????? 输出数组?? ${strArray[1]}
???????????????????? 输出list?? ${list[1].name}
????????????????????
el表达式的运算?
?????????????? ${1+2}=?????? 3
?????????????? ${10/5}=????? 2.0
?????????????? ${10%3}=????? 1
?????????????? ${10 div 2}=? 5.0
?????????????? ${10 mod 4}=? 2
??????????????
el表达式对应的运算符
???????????????????? 等于? ==??? eq
?????????????????? 不等于? !=??? ne
???????????????????? 大于? >???? gt
???????????????????? 小于? <???? lt
???????????????? 大于等于? >=??? ge
???????????????? 小于等于? <=??? le
?????????????????????? 与? &&??? or
?????????????????????? 或? ||??? and
?????????????????????? 非? !???? not
?????????????????????? 加? +
?????????????????????? 减? -
?????????????????????? 乘? *
???????????????????? 除以? /???? div
???????????????????? 求莫? %???? mod
????????????????????
el表达式判断是否为空
??????????????????? request.setAttribute("value1",null)??????????????????? ${empty requestScope.value1} = true
??????????????????? request.setAttribute("value2","")????????????????????? ${empty requestScope.value1} = true
??????????????????? request.setAttribute("value3",new ArrayList())???????? ${empty requestScope.value1} = true
??????????????????? request.setAttribute("value4","i love you")??????????? ${empty requestScope.value1} = false
??????????????????? request.setAttribute("value4","i love you")??????????? ${!empty requestScope.value1} = true