2019-04-14 EL（Expression Language）
EL全名为Expression langusage
它是JSTL 1.0为方便存取数据所定义的语言
1 <!-- 7. EL 的运算符 --> 2 ${param.score > 60 ? "及格" : "不及格" } 3 <br> 4 5 <% 6 List<String> names = new ArrayList<String>(); 7 names.add("abc"); 8 request.setAttribute("names", names); 9 %> 10 <!-- empty 可以作用于一个集合, 若该集合不存在或集合中没有元素, 其结果都为 true --> 11 names is empty: ${empty requestScope.names } 12 <br> 13 14 <!-- 6. 其他隐含对象: pageContext 等(cookie, header, initParam 只需了解.) --> 15 pageContext: pageContext 即为 PageContext 类型, 但只能读取属性就可以一直的 . 下去。 16 <br> 17 contextPath: ${pageContext.request.contextPath } 18 19 <br> 20 sessionId: ${pageContext.session.id } 21 22 <br> 23 sessionAttributeNames: ${pageContext.session.attributeNames } 24 25 <br> 26 27 28 initParam: ${initParam.initName } 29 <br> 30 31 Accept-Language: ${header["Accept-Language"] } 32 <br> 33 34 JSESSIONID: ${cookie.JSESSIONID.name } -- ${cookie.JSESSIONID.value } 35 <br> 36 37 <!-- 5. 与输入有关的隐含对象: param, paramValues --> 38 score: ${param.score } 39 <%-- 40 <%= request.getParameter("score") %> 41 --%> 42 <br> 43 names: ${paramValues.name[0].class.name } 44 <%-- 45 <%= 46 request.getParameterValues("name")[0].getClass().getName() 47 %> 48 --%> 49 <br> 50 51 <!-- 4. 隐含对象之与范围相关的: pageScope, requestScope, sessionScope, applicationScope --> 52 time: ${applicationScope.time.time } 53 <%-- 54 <%= application.getAttribute("time") %> 55 --%> 56 <br> 57 58 <!-- 3. EL 可以进行自动的类型转换 --> 59 score: ${param.score + 11} 60 <br> 61 score: <%= request.getParameter("score") + 11 %> 62 <br> 63 64 <!-- 2. EL 中的隐含对象 --> 65 <% 66 Customer cust2 = new Customer(); 67 cust2.setAge(28); 68 request.setAttribute("customer", cust2); 69 %> 70 71 age: ${customer.age } 72 73 <br> 74 <!-- 1. EL 的 . 或 [] 运算符 --> 75 age: ${sessionScope.customer["age"] } 76 77 <%-- 78 Customer customer = (Customer)session.getAttribute("customer"); 79 out.print(customer.getAge()); 80 --%> 81 82 <% 83 Customer customer = new Customer(); 84 customer.setName("ATGUIGU"); 85 86 session.setAttribute("com.atguigu.customer", customer); 87 %> 88 89 <br> 90 <!-- 91 如果域对象中的属性名带有特殊字符, 则使用 [] 运算符会很方便. 92 --> 93 name: ${sessionScope["com.atguigu.customer"].name }
