ER表达式

ER表达式

概念：是工作在视图组件的技术，完成对内置对象的属性的获取并进行处理，把处理结果发给浏览器进行显示。
对环境的要求：jsp1.2, j2ee2.0, tomcat4.0
基本语法： ${表达式}

如：

• eldemo01.jsp

<%@ page isELIgnored="false"%> 
<%
	pageContext.setAttribute("name","www.zte.cn");
   
%>
 <%=pageContext.getAttribute("name")%>
 <br>
 #####${name} 

• eldemo01.jsp

  <%@ page isELIgnored="false"%> 
  <%
  	pageContext.setAttribute("name","www.zte.cn");
     
  %>
   <%=pageContext.getAttribute("name123")%>
   <br>
   #####${name123} 
  

• eldemo01.jsp

  <%@ page isELIgnored="true"%> 
  <%
  	pageContext.setAttribute("name","www.zte.cn");
     
  %>
   <%=pageContext.getAttribute("name123")%>
   <br>
   #####${name123} 
  

1. EL表达式的搜索顺序和隐式对象从隐式对象中获得数据

• eldmo02.jsp

  <%
  	pageContext.setAttribute("name","www.zte.cn") ;
  	request.setAttribute("name","tom") ;
  %>
  <h1>****${sessionScope.name}</h1>
  

2. EL表达式的处理

• eldemo00.jsp

  <% 
   pageContext.setAttribute("a","30"); 
   request.setAttribute("b",5);
  %> 
  <h1><%=request.getAttribute("c")%></h1><br>
    <h1>---c=${c}----</h1><br>
  <h1>---a*b+c+6=${a*b+c+6}---</h1><br>
  <h1>---a>b=${a>b}---</h1><br>
   
  <h1>----3+5*2=${3+5*2}-----</h1>
  

3. EL表达式在MVC中的应用

3.1 EL表达式处理字符串

自动转换成整型

• ELServletDemo01.java

  package cn.zte.pxb.servlet.el ;
  import java.io.* ;
  import javax.servlet.* ;
  import javax.servlet.http.* ;
  
  public class ELServletDemo01 extends HttpServlet
  {
      
  	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
  	{
  		req.setAttribute("name","www.zte.cn") ;
  		// 服务器端跳转
  		req.getRequestDispatcher("eldemo03.jsp").forward(req,resp) ;
  	}
  	public void doPost(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
  	{
  		this.doGet(req,resp) ;
  	}
  }
  /*
    <servlet>
  	<servlet-name>el01</servlet-name>
  	<servlet-class>cn.zte.pxb.servlet.el.ELServletDemo01</servlet-class>
      <load-on-startup>0</load-on-startup>
    </servlet>
    <servlet-mapping>
  	<servlet-name>el01</servlet-name>
  	<url-pattern>/eldemo/el_1</url-pattern>
    </servlet-mapping>
  */
  

• eldemo03.jsp

   <h1>${name}</h1>
  

3.2 EL表达式处理Bean对象的属性–导航

• Simple.java

  package cn.cx.servlet.el ;
  public class Simple
  {
  	private String name;
  	public Simple()
      {}
  	public void setName(String name)
  	{
  		this.name = name ;
  	}
  	public String getName()
  	{
  		return this.name ;
  	}
  }
  

• ELServletDemo02.java

  package cn.cx.servlet.el ;
  
  import java.io.* ;
  import javax.servlet.* ;
  import javax.servlet.http.* ;
  
  public class ELServletDemo02 extends HttpServlet
  {
  	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
  	{          Simple s=null;
  		      //System.out.println(s);
  			   s = new Simple() ;
  		s.setName("lisa") ;
  		req.setAttribute("sim",s) ;
  		// 服务器端跳转
  		req.getRequestDispatcher("eldemo04.jsp").forward(req,resp) ;
  	}
  	public void doPost(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
  	{
  		this.doGet(req,resp) ;
  	}
  };
  /*
    <servlet>
  	<servlet-name>el02</servlet-name>
  	<servlet-class>cn.cx.servlet.el.ELServletDemo02</servlet-class>
      <load-on-startup>0</load-on-startup>
    </servlet>
    <servlet-mapping>
  	<servlet-name>el02</servlet-name>
  	<url-pattern>/eldemo/el_2</url-pattern>
    </servlet-mapping>
  */
  

• eldemo04.jsp

  <h1>***${sim.name}      //其实sim对象的方法，而不是属性
  

4. el表达式深度导航

• CompanyBean.java

  package cn.cx.servlet.el ;
  public class CompanyBean
  {
  	private String companyName ;
  	private String business ;
  	
  	public CompanyBean()
  	{}
  	public void setCompanyName(String companyName)
  	{
  		this.companyName = companyName ;
  	}
  	public void setBusiness(String business)
  	{
  		this.business = business ;
  	}
  	public String getCompanyName()
  	{
  		return this.companyName ;
  	}
  	public String getBusiness()
  	{
  		return this.business ;
  	}
  };
  

• NameBean.java

  package cn.cx.servlet.el ;
  
  public class NameBean
  {
  	private String firstName ;
  	private String lastName ;
  
  	public NameBean()
  	{}
  	public void setFirstName(String firstName)
  	{
  		this.firstName = firstName ;
  	}
  	public void setLastName(String lastName)
  	{
  		this.lastName = lastName ;
  	}
  	public String getFirstName()
  	{
  		return this.firstName ;
  	}
  	public String getLastName()
  	{
  		return this.lastName ;
  	}
  };
  

• EmployeeBean.java

  package cn.cx.servlet.el ;
  
  public class EmployeeBean
  {
  	private NameBean name;//多个公司可以雇佣一个人员 
  	private CompanyBean company;//多个员工可以被一个公司雇佣
  
  	public EmployeeBean()
  	{}
  	public void setName(NameBean name)
  	{
  		this.name = name ;
  	}
  	public void setCompany(CompanyBean company)
  	{
  		this.company = company ;
  	}
  	public NameBean getName()
  	{
  		return this.name ;
  	}
  	public CompanyBean getCompany()
  	{
  		return this.company ;
  	}
  }
  

• ELServletDemo03.java

  package cn.cx.servlet.el ;
  
  import java.io.* ;
  import javax.servlet.* ;
  import javax.servlet.http.* ;
  
  public class ELServletDemo03 extends HttpServlet
  {
  	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
  	{
  		NameBean nb = new NameBean() ;
  		nb.setFirstName("Li") ;
  		nb.setLastName("sa") ;
  		
  		CompanyBean cb = new CompanyBean() ;
  		cb.setCompanyName("www.cx.cn") ;
  		cb.setBusiness("JAVA EE、JAVA SE、JAVA ME") ;
  
  		EmployeeBean eb = new EmployeeBean() ;
  		eb.setName(nb) ;
  		eb.setCompany(cb) ;
  
  		// 保存属性
  		req.setAttribute("emp",eb) ;
          //request.getAttribute("emp").getName().getFirstName();
  		// 服务器端跳转
  		req.getRequestDispatcher("eldemo05.jsp").forward(req,resp) ;
  	}
  	public void doPost(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
  	{
  		this.doGet(req,resp) ;
  	}
  };
  /*
    <servlet>
  	<servlet-name>el03</servlet-name>
  	<servlet-class>cn.cx.servlet.el.ELServletDemo03</servlet-class>
    </servlet>
    <servlet-mapping>
  	<servlet-name>el03</servlet-name>
  	<url-pattern>/eldemo/el_3</url-pattern>
    </servlet-mapping>
  */ 
  

• eldemo05.jsp

  <h1>FirstName:${emp.name.firstName}</h1><br>
  <h1>BusinessName:${emp.company.companyName}</h1>
  <h1>CompanyBusiness:${emp.company.business}</h1>
  

  

5. el表达式在集合中的应用

• ELServletDemo04.java

  package cn.cx.servlet.el ;
  
  import java.io.* ;
  import java.util.* ;
  import javax.servlet.* ;
  import javax.servlet.http.* ;
  
  public class ELServletDemo04 extends HttpServlet
  {
  	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
  	{
  		List<Simple> l = new ArrayList<Simple>() ;
  		Simple s = null ;
  		s = new Simple() ;
  		s.setName("zhangsan") ;
  		l.add(s) ;
  
  		s = new Simple() ;
  		s.setName("lisi") ;
  		l.add(s) ;
  
  		s = new Simple() ;
  		s.setName("wangwu") ;
  		l.add(s) ;
  
  		req.setAttribute("all",l) ;
  		// 服务器端跳转
  		req.getRequestDispatcher("eldemo06.jsp").forward(req,resp) ;
  	}
  	public void doPost(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
  	{
  		this.doGet(req,resp) ;
  	}
  };
  /*
    <servlet>
  	<servlet-name>el02</servlet-name>
  	<servlet-class>cn.cx.servlet.el.ELServletDemo04</servlet-class>
      <load-on-startup>0</load-on-startup>
    </servlet>
    <servlet-mapping>
  	<servlet-name>el02</servlet-name>
  	<url-pattern>/eldemo/el_4</url-pattern>
    </servlet-mapping>
  */
  

• eldemo06.jsp

  <%@page import="java.util.*"%>
  <%--
  	要使用Iterator进行输出
  --%>
  <h1>${all}</h1><br>
  <h1>${all[2].name}</h1><br>
  <%
  	// List要使用Iterator输出
  	List l = (List)request.getAttribute("all") ;
  	Iterator iter = l.iterator() ;
  	while(iter.hasNext())
  	{
  		// 将取出的对象放在page范围之中
  		 pageContext.setAttribute("sim",iter.next()) ;
          //simple s=(simple)(iter.next());
           //<%=s.getName()%>
  
  		<h1>${sim.name}</h1>
  <%
  	}
  %>