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JSP basic syntax
jsp expression
<%--将程序的结果输出到客户端，可写变量或者表达式--%>
<%=new Date()%>
jsp script fragment
<%--jsp脚本片段--%>
<%
int sum = 0;
for (int i = 0; i < 100; i++) {
sum += i;
}
out.println("<h1>sum:" + sum + "</h1>");
%>
Reimplementation of script fragments
<%
for (int i = 0; i < 5; i++) {
%>
<h5>这是第<%=i%>次展示</h5>
<%
}
%>
jsp statement
<%!
int globalVar = 0;
static {
System.out.println("看看在哪...");
}
public void look(){
System.out.println("再看看在哪...");
}
%>
Look at the difference between source code analysis <% %> / <%! %> (see the comments)
Overall source code: index_jsp.java
/*
* Generated by the Jasper component of Apache Tomcat
* Version: Apache Tomcat/8.5.47
* Generated at: 2021-01-22 03:30:32 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.Date;
public final class index_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent,
org.apache.jasper.runtime.JspSourceImports {
//<%! %>中声明的
/*int globalVar = 0;
static {
System.out.println("看看在哪...");
}
public void look(){
System.out.println("再看看在哪...");
}*/
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 = new java.util.HashSet<>();
_jspx_imports_classes.add("java.util.Date");
}
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("<body>\n");
out.write("<h2>Hello World!</h2>\n");
out.write('\n');
out.print(new Date());
out.write('\n');
out.write('\n');
//以下为<%= %>和<% %>中声明的
/*int sum = 0;
for (int i = 0; i < 100; i++) {
sum += i;
}
out.println("<h1>sum:" + sum + "</h1>");
out.write("\n");
out.write("\n");
out.write("<hr>\n");
for (int i = 0; i < 5; i++) {
out.write("\n");
out.write("<h5>这是第");
out.print(i);
out.write("次展示</h5>\n");
}
out.write("\n");
out.write("<hr>\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);
}
}
}
It can be seen that the declaration in <%! %> is placed in the index_jsp class, and other declarations are placed in the _jspService method
<% %>
<%= %>
<%! %>
<%--注释--%>
Comment
<!--html注释 可以通过网页上的f12查看到-->
<%--jsp注释--%>
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