jsp 之 入门 jsp代码块
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1.jsp脚本 (3种代码块)
1.<% JAVA代码块 %>
2.<%= JAVA变量或者表达式%>
3.<%! JAVA代码块%>
方法1:<% java代码 %>
特点:内部的java代码直接翻译到Servlet方法内部
如图所示:
jsp窗口:
jsp生成的Servlet窗口:
方法2:<%= java变量或者表达式 %>
特点:相当于out.print(java变量或者表达式)
jsp窗口:
jsp生成的Servlet窗口:
方法3:<%! java代码 %>
特点:存放在Servlet方法块里
jsp窗口:
jsp生成的Servlet窗口:
index.jsp代码
<%@ page contentType="text/html;charset=UTF-8" language="java" %><html><head> <title>我的网页</title></head><body><% int i=0; out.print(i);%><%=i+3%><%! public class Student { int age; String name; public Student(String name,int age) { this.age = age; this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return "Student{" + "age=" + age + ", name='" + name + '\'' + '}'; } }%><% Student me = new Student("神奇的我", 12); out.println(me.toString());%></body></html>生成的index_jsp.java 代码 （具体可以在Tomcat的work下找到）
/* * Generated by the Jasper component of Apache Tomcat * Version: Apache Tomcat/9.0.1 * Generated at: 2017-12-03 14:54:33 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.web;import javax.servlet.*;import javax.servlet.http.*;import javax.servlet.jsp.*;public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase implements org.apache.jasper.runtime.JspSourceDependent, org.apache.jasper.runtime.JspSourceImports { public class Student { int age; String name; public Student(String name,int age) { this.age = age; this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return "Student{" + "age=" + age + ", name='" + name + '\'' + '}'; } } 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 static final java.util.Set<java.lang.String> _jspx_imports_packages; private static final java.util.Set<java.lang.String> _jspx_imports_classes; static { _jspx_imports_packages = new java.util.HashSet<>(); _jspx_imports_packages.add("javax.servlet"); _jspx_imports_packages.add("javax.servlet.http"); _jspx_imports_packages.add("javax.servlet.jsp"); _jspx_imports_classes = null; } private volatile javax.el.ExpressionFactory _el_expressionfactory; private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager; public java.util.Map<java.lang.String,java.lang.Long> getDependants() { return _jspx_dependants; } public java.util.Set<java.lang.String> getPackageImports() { return _jspx_imports_packages; } public java.util.Set<java.lang.String> getClassImports() { return _jspx_imports_classes; } public javax.el.ExpressionFactory _jsp_getExpressionFactory() { if (_el_expressionfactory == null) { synchronized (this) { if (_el_expressionfactory == null) { _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory(); } } } return _el_expressionfactory; } public org.apache.tomcat.InstanceManager _jsp_getInstanceManager() { if (_jsp_instancemanager == null) { synchronized (this) { if (_jsp_instancemanager == null) { _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig()); } } } return _jsp_instancemanager; } public void _jspInit() { } 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 java.lang.String _jspx_method = request.getMethod(); if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method) && !javax.servlet.DispatcherType.ERROR.equals(request.getDispatcherType())) { response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSPs only permit GET POST or HEAD"); return; } 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("\n"); out.write("\n"); out.write("<html>\n"); out.write("<head>\n"); out.write("<title>我的网页</title>\n"); out.write("</head>\n"); out.write("<body>\n"); int i=0; out.print(i); out.write('\n'); out.print(i+3); out.write('\n'); out.write('\n'); out.write('\n'); Student me = new Student("神奇的我", 12); out.println(me.toString()); out.write("\n"); out.write("\n"); out.write('\n'); out.write("\n"); out.write("</body>\n"); out.write("</html>\n"); } catch (java.lang.Throwable t) { if (!(t instanceof javax.servlet.jsp.SkipPageException)){ out = _jspx_out; if (out != null && out.getBufferSize() != 0) try { if (response.isCommitted()) { out.flush(); } else { 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); } }}阅读全文
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