el表达式

EL表达式

只要是支持Servlet2.4或JSP2.0的容器，就可以在JSP页面中直接使用EL

所有EL都是以${为起始，以}为结尾的。

如

${sessionScope.person.name}等效于

<%

Personperson=(Person)session.getAttribute("person");

Stringname=person.getName();

out.println(name);

%>

EL提供.与[]两种运算符来存取数据

普通字符串

request.setAttribute("hello","helloworld");

${hello}

el的隐含对象pageScope,requestScope,sessionScope,applicationScope,如果未指定 scope,它的搜索顺序为pageScope-->requestScope-->sessionScope-->applicationScope

对象

Groupgroup=newGroup();

group.setName("尚学堂");

Useruser=newUser();

user.setUsername("张三");

user.setAge(18);

user.setGroup(group);

request.setAttribute("user",user);

${user.username}<br>${user.age}<br>${user.group.name}<br>

map

MapmapValue=newHashMap();

mapValue.put("key1","value1");

mapValue.put("key2","value2");

request.setAttribute("mapvalue",mapValue);

${mapvalue.key1}<br>${mapvalue.key2}<br>

字符串数组

String[]strArray=newString[]{"a","b","c"};

request.setAttribute("strarray",strArray);

${strarray[0]}<br>${strarray[1]}<br>${strarray[2]}<br>

对象数组

User[]users=newUser[10];

for(inti=0;i<10;i++){

Useru=newUser();

u.setUsername("U_"+i);

users[i]=u;

}

request.setAttribute("users",users);

${users[0].username}<br>${users[1].username}<br>${users[2].username}<br>

list

ListuserList=newArrayList();

for(inti=0;i<10;i++){

Useruu=newUser();

uu.setUsername("UU_"+i);

userList.add(uu);

}

request.setAttribute("userlist",userList);

${userlist[4].username}

测试empty

request.setAttribute("value1",null);

request.setAttribute("value2","");

request.setAttribute("value3",newArrayList());

request.setAttribute("value4","123456");

value1:${emptyvalue1}<br>

value2:${emptyvalue2}<br>

value3:${emptyvalue3}<br>

value4:${emptyvalue4}<br>

value4:${!emptyvalue4}<br>

取web.xml初始化参数

<context-param>

<param-name>encoding</param-name>

<param-value>大五码</param-value>

</context-param>

${initParam.encoding}

取URL参数

<ahref="el.jsp?a=aaa&b=bbb">链接ELp2</a>

${param.a}<br>${param.b}<br>

el表达式支持运算符

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