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1 //servlet中,: 2 user user = new user(1,"admin","admin","hahahaha"); 3 httpsession session =request.getsession(); 4 session.setattribute("user",user); 5 response.sendredirect("index.jsp");
//index.jsp中,加判断,避免空指针异常 user user =(user)session.getattribute("user"); if(user!=null){ out.write(,欢迎"+user.getrealname()+"光临本站"); }else{ out.write(",欢迎光临本站!"); }
<%-- 可能会报500异常: ,欢迎<%= ((user)session.getattribute("user")).getrealname() %>光临本站! --%> <%-- 更为简单,稳妥的方式! --%> 欢迎${user.realname}光临本站!
<body> <%-- 加判断,避免空指针异常 <% user user = (user)session.getattribute("user"); if(user != null){ out.write("欢迎"+user.getrealname()+"光临本站!"); }else{ out.write("欢迎光临本站!"); } %> --%> <%-- 可能会报500异常: 欢迎<%= ((user)session.getattribute("user")).getrealname() %>光临本站! --%> <%-- 更为简单,稳妥的方式! --%> <% int a = 10; //数据在四大作用域对象中 pagecontext.setattribute("a", a); request.setattribute("aaa", true); session.setattribute("age", 18); application.setattribute("name", "laowang"); // 简单对象 user user = new user(1, "admin", "admin", "老王"); request.setattribute("uuu", user); // 复合对象 user u2 = new user(2, "admin-laowang", "123123", "老王", new address( "广东省", "广州市", "天河区")); pagecontext.setattribute("u2", u2); //list中的数据 list list = new arraylist(); list.add("apple"); list.add("orange"); list.add("watermelon"); list.add("pineapple"); pagecontext.setattribute("fruits", list); //map中的数据 map map = new hashmap(); map.put("name", "zhangsan"); map.put("age", 18); map.put("gender", "女"); map.put("address", new address("广东省", "广州市", "天河区")); pagecontext.setattribute("person1", map); //作用域中有相同的key pagecontext.setattribute("xxx", "pagecontext"); request.setattribute("xxx", "request"); session.setattribute("xxx", "session"); application.setattribute("xxx", "application"); user uu1 = new user(5,"admin","admin","张三"); user uu2 = new user(5,"admin","admin","张三"); request.setattribute("uu1", uu1); request.setattribute("uu2", uu2); request.setattribute("score", 99); pagecontext.setattribute("a1", null); pagecontext.setattribute("a2", new arraylist()); pagecontext.setattribute("a3", new hashmap()); pagecontext.setattribute("a4", ""); %> 欢迎${user.realname}光临本站! <h3>el表达式从哪里取值?一般情况下,从作用域对象中取值</h3> ${a} --- ${aaa} --- ${age} --- ${name} <h3>el表达式可以取什么类型的值?基本数据类型、引用数据类型(对象、复合对象、list、map)</h3> ${uuu.realname} --- ${u2.addr.town} --- ${fruits[2]} --- ${person1.address.city} <h3>el表达式从哪个作用域中取值?默认从最小作用域中开始寻找,找不到往大的作用域中找,都找不到显示为空</h3> ${xxx} <h3>el从指定作用域中取值? pagescope、requestscope、sessionscope、applicationscope</h3> ${pagescope.xxx }--- ${requestscope.xxx} --- ${sessionscope.xxx } --- ${applicationscope.xxx } <h3>el表达式还可以取请求参数中的值:param、paramvalues</h3> ${param.username} --- ${paramvalues.fav[2] } <h3>el表达式除了“.”操作符之外,还有“[ ]”操作符:“[]”可以解析子el表达式</h3> ${uuu["realname"]} --- ${param.type} --- ${uuu[param.type]} <h3>el表达式中的为空判断:empty判断为空的有:空字符串、null、空集合、空map</h3> ${empty a1} --- ${empty a2} --- ${empty a3} --- ${empty a4} <h3>el表达式可以进行一些基本的数学运算</h3> ${5+4} --- ${5-4} --- ${5*4} --- ${5/4} --- ${5%4} --- ${5+"4"} <h3>el表达式可以进行一些逻辑判断</h3> ${5>4} --- ${ 5 == 4} --- ${ 5 eq 4 } --- ${uu1 == uu2} --- ${uu1 eq uu2} --- ${score == 99 } </body>
<body> <% request.setattribute("weather", "今天天气很热!"); pagecontext.setattribute("aaa", "aaa"); request.setattribute("aaa", "bbb"); session.setattribute("aaa", "ccc"); application.setattribute("aaa", "ddd"); request.setattribute("score", 78); list list = new arraylist(); user u1 = new user(1, "admin", "admin", "老王"); user u2 = new user(2, "cai10", "admin", "蔡依林"); user u3 = new user(3, "cai20", "admin", "蔡依林"); user u4 = new user(4, "cai30", "admin", "蔡依林"); user u5 = new user(5, "cai40", "admin", "蔡依林"); list.add(u1); list.add(u2); list.add(u3); list.add(u4); list.add(u5); request.setattribute("persons", list); date date = new date(); request.setattribute("d1", date); string datestr = "1999/12/12 03:04:05"; request.setattribute("ds", datestr); string str2 = "18810950652"; request.setattribute("phone", str2); %> <h3>c:out标签:用于将作用域中的对象输出,default属性会在value属性为空时显示</h3> <c:out value="${weather}" default="汗流浃背!"></c:out> <h3>c:set标签:用于将一个数据保存在作用域中(默认最小作用中),通过scope设定存放的作用域</h3> <c:set var="name" value="laowang" scope="request"></c:set> ${requestscope.name} <c:set var="table"> <table border="1" style="border-collapse: collapse;"> <tr> <td>1*1</td> <td>1*2</td> </tr> <tr> <td>2*1</td> <td>2*2</td> </tr> </table> </c:set> ${table}-${table}-${table} <h3>c:remove标签:将作用域中的指定key的数据删除(默认删除所有作用域中的指定key的数据)</h3> <c:remove var="aaa" scope="page" /> ${aaa} <h3>c:if标签:条件判断(单条件)</h3> <c:if test="${score >= 80}" var="flag"> 优秀! </c:if> <c:if test="${!flag}"> 良好! </c:if> <h3>c:choose 、 c:when、 c:otherwise标签:条件判断(多条件)</h3> <h4>注意以下几点:1.c:when必须在c:otherwise之前出现</h4> <h4>2.c:otherwise只能出现一次</h4> <h4>3.c:when和c:when和c:otherwise之前不允许出现其他任何字符</h4> <c:choose> <c:when test="${score >=80 }"> 优秀! </c:when> <c:when test="${score >=70 }"> 良好 </c:when> <c:when test="${score >=60 }"> 及格 </c:when> <c:otherwise> 不及格 </c:otherwise> </c:choose> <h3>c:foreach标签:循环</h3> <h4>items:循环体,通过使用el表达式获取循环的内容</h4> <h4>begin & end:只能为数字,当没有items属性时,从begin数字循环到end数字;当有items属性时,begin & end就表示下标</h4> <h4>step:步长</h4> <h4>var:表示每次的循环体</h4> <h4>varstatus:当前循环体的状态:有几个属性--first(判断当前循环体是否为第一个)、last(判断当前循环体是否为最后一个)、count(当前循环次数)、index(当前循环体的下标)</h4> <c:foreach begin="3" end="9" var="each"> ${each} </c:foreach> <br> <c:foreach items="4123,2512,222,111,555,677,999" begin="1" end="3" var="each"> ${each} </c:foreach> <br> <c:foreach items="${persons}" step="2" var="person"> ${person.username}<br> </c:foreach> <br> <c:foreach items="${persons}" var="person" step="2" varstatus="status"> ${person.username} --- ${status.first} --- ${status.last} --- ${status.count} --- ${status.index}<br> </c:foreach> <br> <table border="1" style="border-collapse: collapse;"> <tr><td>id</td><td>用户名</td><td>真实姓名</td></tr> <c:foreach items="${persons}" var="person"> <tr><td>${person.id}</td><td>${person.username }</td><td>${person.realname }</td></tr> </c:foreach> </table> <h3>c:redirect标签:重定向</h3> <%-- <c:redirect url="http://www.baidu.com"></c:redirect> --%> <h3>c:import标签:指定一个url的页面在本页面中</h3> <%--<c:import url="http://www.baidu.com"></c:import> --%> <fmt:formatdate value="${d1}" pattern="yyyy年mm月dd日 hh时mm分ss秒"/> <fmt:parsedate value="${ds}" var="d2" pattern="yyyy/mm/dd hh:mm:ss"></fmt:parsedate> //计算长度 ${fn:length(phone) } </body>
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