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EL表达式的出现其实是用来排挤JSP的。因为JSP的代码既有前端html的各种标签，还带有java的逻辑代码，这样就会导致前后端没有完全分离，代码看起来也蛮不爽的。为了解决这个问题，EL表达式横空出世了。

直接举例子吧：

public class Student {   private int sno;private String sname;private Address address;public Student() {    }public Student(int sno, String sname, Address address) {    super(); this.sno = sno; this.sname = sname; this.address = address;}public int getSno() {    return sno;}public void setSno(int sno) {    this.sno = sno;}public String getSname() {    return sname;}public void setSname(String sname) {    this.sname = sname;}public Address getAddress() {    return address;}public void setAddress(Address address) {    this.address = address;}}

Student的级联属性类：

public class Address {   private String homeAddress;private String schoolAddress;public Address() {    }public Address(String homeAddress, String schoolAddress) {    super(); this.homeAddress = homeAddress; this.schoolAddress = schoolAddress;}public String getHomeAddress() {    return homeAddress;}public void setHomeAddress(String homeAddress) {    this.homeAddress = homeAddress;}public String getSchoolAddress() {    return schoolAddress;}public void setSchoolAddress(String schoolAddress) {    this.schoolAddress = schoolAddress;}}

现在先在request中加入Student的一个对象

<%  Student student = new Student();  student.setSno(1);  student.setSname("luzelong");  Address address = new Address();  address.setHomeAddress("qq");  address.setSchoolAddress("aa");  student.setAddress(address);  request.setAttribute("student", student);%>

获取student的信息（下面列出两种方式）

----------------------点操作符-------------------
        ${requestScope.student}
        ${requestScope.student.sno}
        ${requestScope.student.sname}
        ${requestScope.student.address.homeAddress}
        ${requestScope.student.address.schoolAddress}
        
           ----------------------[""]操作符-------------------
        ${   requestScope.student['address']["schoolAddress"]}

而类比一下jsp的写法：(是不是感觉少了很多代码，而且看起来更爽)

<%         Student student = (Student) request.getAttribute("student");         out.print(student+"
");         out.print(student.getSno()+"
");         out.print(student.getSname()+"
");         //out.print(student.getAddress()+"
");         out.print(student.getAddress().getHomeAddress()+"
");         out.print(student.getAddress().getSchoolAddress()+"
");%>

上面打印的结果都是：

给session域中放一个数组和Map：

String[] POW= new String[] {   "AA","BB","CC"};  session.setAttribute("POW", POW);    Map
   
     map = new HashMap<>();  map.put("cf","穿越火线");  map.put("cs", "反恐精英");  session.setAttribute("map",map);
   

EL取出上面的单个值

${sessionScope.POW[0]}
        ${sessionScope.POW[1]}
        ${sessionScope.POW[2]}
         ${sessionScope.map.cf}
        ${   sessionScope.map["cs"]}

输出结果为：

EL的简单判断：

${9>1}、${9 gt 2}、${9>2 || 9<2}、${9>2 or 9<2}   

上面的都为true!

${empty requestScope["DDD"]}

获取地址的栏的参数

${test}    ${requestScope.test}      <%request.getAttribute("test"); %>

以上的方法均不能获取。

${param.test}

输出结果为1

${pageContext.request.serverPort}

看完这篇相信各位对el基本掌握了，希望点个赞关注一下吧_{_}