一、EL表达式(形式:${ })
1. EL运算符
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- 算术运算符: +、-、*、/、%
示例 结果
${1+1} 2
${1-1} 0
${1*3} 3
${3/2} 1.5
${5%3} 2
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-
关系运算符:大于、小于、等于、不等于、大于等于、小于等于
-
示例 结果
${2>1} true
${1<0} false
${1==1} true
${3!=2} true
${5>=2} true
${4<=3} false
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逻辑运算符: ||、&&、!
-
示例 结果
${true||true} true
${true||false} true
${false||false} false
${true&&true} true
${true&&false} false
${false&&false} false
${!true} false
${!false} true
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-
条件运算符:${A?B:C}
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示例: ${2>1? "true" : "false"} 结果 true
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验证运算符:${empty var}
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String username = "tom";
${empty username} 结果 true
2. EL内置对象
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域对象
- pageScope
- requestScope
- sessionScope
- applicationScope
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输入对象
- param // param.username 相当于 request.getParameter("username");
- paramValues // paramValues.hobby相当于 request.getParameterValues("hobby");
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Cookie对象
- ${cookie.username.value} //获取cookie中username属性的值
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initParam对象
- ${initParam.username} // 获取context对象中的参数值
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如:
<context-param>
<param-name>username</param-name>
<param-value>tom</param-value>
</context-param>
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pageContext对象
- ${pageContext.request.requestURL} //获取请求URL
- ${pageContext.request.queryString} //获取参数字符串
- ${pageContext.request.contextpath} //获取当前应用目录
- ${pageContext.request.method} //获取请求方式
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3. EL存取器
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- 获取JavaBean数据
${sessionScope.person.name}
${sessionScope.person.age}
- 获取Map数据
// HashMap userInfo= new HashMap(); userInfo.put("username","tom"); userInfo.put("password","123456");
- 获取JavaBean数据
${userInfo.username}
${userInfo.password}
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- 获取数组数据
${names[0]} // String names = {"tom","lisa","jerry"}
${names[0]}