el表达式中的内置对象 · Java

# 把作用域对象映射为一个map对象 1. pageScope 2. requestScope 3. sessionScope 4. applictionScope ## param 表示了一个保存了所有请求参数的Map对象.只能针对单值使用,获取多值的时候只能获取到第一个. ``` http://localhost:8080/dome/product.jsp?name=jack&age=20&hobby=game&hobby=swimming ``` ~~~ ${param} ${param.get("name")} ${param.name} ${param.get("age")} ${param.age} ${param.hobby} ~~~ 结果 ``` {name=jack, age=20, hobby=game} jack jack 20 20 game ``` ## paramValues 表示了一个保存了所有请求参数的Map对象,它对于某个请求参数,返回的是一个string[] ``` http://localhost:8080/dome/product.jsp?name=jack&age=20&hobby=game&hobby=swimming ``` ~~~ ${paramValues} <br> ${paramValues.name[0]} ${paramValues.age[0]} ${paramValues.hobby[0]} ${paramValues.hobby[1]} ~~~ 结果注意看下面 ,花括号表示map,只有左中括号代表是数组,有@符号代表是对象. ``` {name=[Ljava.lang.String;@7e0dd5a, age=[Ljava.lang.String;@68db662a, hobby=[Ljava.lang.String;@2f98874e} jack 20 game swimming ``` ## header 表示一个保存了所有http请求头字段的map对象. ~~~ ${header} <hr> ${header["user-agent"]} ~~~ ``` {accept-language=zh-CN,zh;q=0.9,en;q=0.8, cookie=JSESSIONID=7526EE46EB0E490649F9FF312805CB5A; \_ga=GA1.1.1990820977.1551056837; \_gid=GA1.1.1782844567.1551171956, host=localhost:8080, upgrade-insecure-requests=1, connection=keep-alive, cache-control=max-age=0, accept-encoding=gzip, deflate, br, user-agent=Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_14\_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36, accept=text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,\*/\*;q=0.8} * * * Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_14\_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36 ``` ## headerValues 表示了一个保存了所有http请求头字段的map对象,它对于某个请求参数,返回的是一个string[]数组. ~~~ ${headerValues} <hr> ${headerValues["user-agent"][0]} ~~~ ``` {accept-language=\[Ljava.lang.String;@374197e9, cookie=\[Ljava.lang.String;@32e58c32, host=\[Ljava.lang.String;@2448f6dd, upgrade-insecure-requests=\[Ljava.lang.String;@57d6d580, connection=\[Ljava.lang.String;@6c93fe4c, cache-control=\[Ljava.lang.String;@72097bf0, accept-encoding=\[Ljava.lang.String;@11148572, user-agent=\[Ljava.lang.String;@708f2805, accept=\[Ljava.lang.String;@39dc9c6} * * * Mozilla/5.0 (Macintosh; Intel Mac OS X 10\_14\_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36 ``` ## initParam 表示一个保存了所有web应用初始化参数的map对象. 在web.xml文件中配置 ~~~ <context-param> <param-name>name</param-name> <param-value>jack</param-value> </context-param> ~~~ ~~~ ${initParam} <br> ${initParam.name} ~~~ ``` {name=jack} jack ``` ## cookie 表示了一个保存了所有cookie的map对象. ~~~ ${cookie} <br> ${cookie.JSESSIONID.value} ~~~ ``` {_ga=javax.servlet.http.Cookie@3f863453, JSESSIONID=javax.servlet.http.Cookie@4e1e1b0a, _gid=javax.servlet.http.Cookie@24597349} F078E28ECF51AF3B545731E606015C12 ``` ## pageContext 对应于JSP页面中的pageContext对象.因为el表达式中没有其他三个域对象. ~~~ ${pageContext.request.contextPath} //获取当前项目路径 ~~~