一、JSP之JSP基础语法

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Java Server Pages

页面元素构成：
注释，声明，小脚本，表达式，指令，静态内容

指令：

page指令：通常位于jsp页面顶端，同一个页面可有多个page指令。

<%@ page contentType="text/html;charset=UTF-8" language="java" import="java.util.*" %>

include指令：将外部文件嵌入到当前jsp文件中，同时解析这个页面中的jsp语句。
taglib指令：使用标签库定义新的自定义标签，在JSP页面中启动定制行为。

注释：

<!-- html注释 -->：客户端可见

<%-- jsp注释 --%>:客户端不可见

可以在脚本中使用java注释：客户端不可见

JSP脚本：客户端不可见

在JSP页面中执行的java代码
<% java代码 %>

声明：客户端不可见

定义变量或方法
<%! java代码 %>

表达式：

<%=表达式 %> //表达式不以分号结束

JSP生命周期

这里写图片描述

index.jsp :

<%@ page contentType="text/html;charset=UTF-8" language="java" import="java.util.*" %><%@ page import="java.text.SimpleDateFormat" %><html>  <head>    <!-- html注释,客户端可见 -->    <title>首页</title>  </head>  <body>  <%!    String s = "kid";    int add(int x, int y) {      return x + y;    }  %>  <%    out.println("welcome " + s);  %>  <%    SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");    String date = sdf.format(new Date());  %>  <br>  x+y=<%=add(1,4)%>  name is <%=s%>  <br>  今天是<%=date%>  </body></html>

index_jsp.java :

/* * Generated by the Jasper component of Apache Tomcat * Version: Apache Tomcat/9.0.0.M21 * Generated at: 2017-06-20 10:56:52 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.*;import java.text.SimpleDateFormat;public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase    implements org.apache.jasper.runtime.JspSourceDependent,                 org.apache.jasper.runtime.JspSourceImports {    String s = "kid";    int add(int x, int y) {      return x + y;    }  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("java.util");    _jspx_imports_packages.add("javax.servlet.http");    _jspx_imports_packages.add("javax.servlet.jsp");    _jspx_imports_classes = new java.util.HashSet<>();    _jspx_imports_classes.add("java.text.SimpleDateFormat");  }  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("\n");      out.write("<html>\n");      out.write("  <head>\n");      out.write("    <!-- html注释,客户端可见 -->\n");      out.write("    <title>首页</title>\n");      out.write("  </head>\n");      out.write("  <body>\n");      out.write("  ");      out.write('\n');      out.write(' ');      out.write(' ');    out.println("welcome " + s);      out.write('\n');      out.write(' ');      out.write(' ');    SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");    String date = sdf.format(new Date());      out.write("\n");      out.write("  <br>\n");      out.write("  x+y=");      out.print(add(1,4));      out.write("\n");      out.write("  name is ");      out.print(s);      out.write("\n");      out.write("  <br>\n");      out.write("  今天是");      out.print(date);      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);    }  }}

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