JSP EL表达式使用

JSP EL表达式使用：

Servlet:

package com.stono.servlet;

import java.io.IOException;

import java.util.HashMap;

import java.util.Map;

import javax.servlet.RequestDispatcher;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import com.stono.servlet.bean.Dog;

import com.stono.servlet.bean.Person;

import com.stono.servlet.bean.Toy;

public class TestServlet6 extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        Person person = new Person();

        Dog dog = new Dog();

        Toy toy = new Toy();

        toy.setName("toyName");

        dog.setName("dogName");

        dog.setToy(toy);

        person.setDog(dog);

        person.setName("personName");

        req.setAttribute("person", person);

        String[] musics = new String[] { "m1", "m2", "m3" };

        req.setAttribute("musics", musics);

        Map<String, Object> map = new HashMap<String, Object>();

        map.put("a", "ma");

        map.put("b", "mb");

        map.put("c", "mc");

        req.setAttribute("map", map);

        Map<String, Object> map2 = new HashMap<String, Object>();

        map2.put("a", "m2a");

        req.setAttribute("map2", map2);

        req.setAttribute("aref", "a");

        RequestDispatcher dispatcher = req.getRequestDispatcher("index016.jsp");

        dispatcher.forward(req, resp);

    }

}

JSP:

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<%

    String path = request.getContextPath();

    String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";

    pageContext.setAttribute("pca", "pageContextAttribute");

    //session.setAttribute("s", "session");

%>

<!DOCTYPE html>

<html>

<head>

<meta charset="UTF-8">

<title>016</title>

</head>

<body>

    <p>JSP生成的java文件中，EL表达式使用统一的方式进行数据读取；</p>

    <p>EL result is : ${pageScope.pca }</p>

    <p>person.name is : ${person.name }</p>

    <p>person.dog.name is : ${person.dog.name }</p>

    <p>musics[0] is : ${musics[0]}</p>

    <p>musics["1"] is : ${musics["1"]}</p>

    <p>musics["2"] is : ${musics[1+1]}</p>

    <p>map[a] is : ${map[a] }</p>

    <p>map["a"] is : ${map["a"] }</p>

    <p>map.a is : ${map.a }</p>

    <p>[]中没有引号，就会计算括号中的内容：</p>

    <p>map2[aref] is : ${map2[aref] }</p>

    <p>map2["aref"] is : ${map2["aref"] }</p>

    <p>person.dog.toy.name is : ${person.dog.toy.name}</p>

    <p>XXX is : ${XXX }</p>

    <p>

        ${pageScope }

        ${requestScope }

        ${sessionScope }

        ${applicationScope }

        ${param }

        ${paramValues }

        ${header }

        ${headerValues }

        ${cookie }

        ${initParam }

        ${pageContext }

    </p>

</body>

</html>

JSP转换生成的Java：

/*

 * Generated by the Jasper component of Apache Tomcat

 * Version: Apache Tomcat/7.0.35

 * Generated at: 2015-10-30 00:31:49 UTC

 * Note: The last modified time of this file was set to

 *       the last modified time of the source file after

 *       generation to assist with modification tracking.

 */

package org.apache.jsp;

import javax.servlet.*;

import javax.servlet.http.*;

import javax.servlet.jsp.*;

import java.util.*;

public final class index016_jsp extends org.apache.jasper.runtime.HttpJspBase

    implements org.apache.jasper.runtime.JspSourceDependent {

  private static final javax.servlet.jsp.JspFactory _jspxFactory =

          javax.servlet.jsp.JspFactory.getDefaultFactory();

  private static java.util.Map<java.lang.String,java.lang.Long> _jspx_dependants;

  private javax.el.ExpressionFactory _el_expressionfactory;

  private org.apache.tomcat.InstanceManager _jsp_instancemanager;

  public java.util.Map<java.lang.String,java.lang.Long> getDependants() {

    return _jspx_dependants;

  }

  public void _jspInit() {

    _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();

    _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());

  }

  public void _jspDestroy() {

  }

  public void _jspService(final javax.servlet.http.HttpServletRequest request, final javax.servlet.http.HttpServletResponse response)

        throws java.io.IOException, javax.servlet.ServletException {

    final javax.servlet.jsp.PageContext pageContext;

    javax.servlet.http.HttpSession session = null;

    final javax.servlet.ServletContext application;

    final javax.servlet.ServletConfig config;

    javax.servlet.jsp.JspWriter out = null;

    final java.lang.Object page = this;

    javax.servlet.jsp.JspWriter _jspx_out = null;

    javax.servlet.jsp.PageContext _jspx_page_context = null;

    try {

      response.setContentType("text/html;charset=UTF-8");

      pageContext = _jspxFactory.getPageContext(this, request, response,

                  null, true, 8192, true);

      _jspx_page_context = pageContext;

      application = pageContext.getServletContext();

      config = pageContext.getServletConfig();

      session = pageContext.getSession();

      out = pageContext.getOut();

      _jspx_out = out;

      out.write('\r');

      out.write('\n');

    String path = request.getContextPath();

    String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";

    pageContext.setAttribute("pca", "pageContextAttribute");

    //session.setAttribute("s", "session");

      out.write("\r\n");

      out.write("<!DOCTYPE html>\r\n");

      out.write("<html>\r\n");

      out.write("<head>\r\n");

      out.write("<meta charset=\"UTF-8\">\r\n");

      out.write("<title>016</title>\r\n");

      out.write("</head>\r\n");

      out.write("<body>\r\n");

      out.write("\t<p>EL result is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${pageScope.pca }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>person.name is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${person.name }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>person.dog.name is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${person.dog.name }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>musics[0] is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${musics[0]}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>musics[\"1\"] is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${musics[\"1\"]}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>musics[\"2\"] is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${musics[1+1]}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>map[a] is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${map[a] }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>map[\"a\"] is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${map[\"a\"] }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>map.a is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${map.a }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>[]中没有引号，就会计算括号中的内容：</p>\r\n");

      out.write("\t<p>map2[aref] is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${map2[aref] }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>map2[\"aref\"] is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${map2[\"aref\"] }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>person.dog.toy.name is : ");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${person.dog.toy.name}", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("</p>\r\n");

      out.write("\t<p>\r\n");

      out.write("\t\t");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${pageScope }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("\r\n");

      out.write("\t\t");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${requestScope }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("\r\n");

      out.write("\t\t");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${sessionScope }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("\r\n");

      out.write("\t\t");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${applicationScope }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("\r\n");

      out.write("\t\t");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${param }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("\r\n");

      out.write("\t\t");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${paramValues }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("\r\n");

      out.write("\t\t");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${header }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("\r\n");

      out.write("\t\t");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${headerValues }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("\r\n");

      out.write("\t\t");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${cookie }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("\r\n");

      out.write("\t\t");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${initParam }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("\r\n");

      out.write("\t\t");

      out.write((java.lang.String) org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate("${pageContext }", java.lang.String.class, (javax.servlet.jsp.PageContext)_jspx_page_context, null, false));

      out.write("\r\n");

      out.write("\t</p>\r\n");

      out.write("</body>\r\n");

      out.write("</html>\r\n");

    } catch (java.lang.Throwable t) {

      if (!(t instanceof javax.servlet.jsp.SkipPageException)){

        out = _jspx_out;

        if (out != null && out.getBufferSize() != 0)

          try { out.clearBuffer(); } catch (java.io.IOException e) {}

        if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);

        else throw new ServletException(t);

      }

    } finally {

      _jspxFactory.releasePageContext(_jspx_page_context);

    }

  }

}

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