从上图中，就可以看出，我们之前创建的HelloWorld.jsp文件，最终是被编译成了HelloWorld_jsp.java文件。
编译之后的JSP文件的命名规则是：XXX_jsp.java、XXX_jsp.class，其中XXX是原先的JSP文件名称。
到这里，我们就可以解释，为什么JSP程序本质上Servlet程序啦。
1.2、编译之后的JSP源代码打开上面编译之后的HelloWorld_jsp.java文件，查看里面的源代码，如下所示：
/*
* Generated by the Jasper component of Apache Tomcat
* Version: Apache Tomcat/8.5.98
* Generated at: 2024-02-24 07:57:25 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 com.gitcode.servlet;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
public final class HelloWorld_jsp extends org.apache.jasper.runtime.HttpJspBase
implements org.apache.jasper.runtime.JspSourceDependent,
org.apache.jasper.runtime.JspSourceImports {
private static final JspFactory _jspxFactory =
JspFactory.getDefaultFactory();
private static java.util.Map<String, Long> _jspx_dependants;
private static final java.util.Set<String> _jspx_imports_packages;
private static final java.util.Set<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<String, Long> getDependants() {
return _jspx_dependants;
}
public java.util.Set<String> getPackageImports() {
return _jspx_imports_packages;
}
public java.util.Set<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 HttpServletRequest request, final HttpServletResponse response)
throws java.io.IOException, ServletException {
final String _jspx_method = request.getMethod();
if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method) && !DispatcherType.ERROR.equals(request.getDispatcherType())) {
response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSP 只允许 GET、POST 或 HEAD。Jasper 还允许 OPTIONS");
return;
}
final PageContext pageContext;
HttpSession session = null;
final ServletContext application;
final ServletConfig config;
JspWriter out = null;
final Object page = this;
JspWriter _jspx_out = null;
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\n");
out.write("<html>\r\n");
out.write("<head>\r\n");
out.write(" <title>Title</title>\r\n");
out.write("</head>\r\n");
out.write("<body>\r\n");
out.write(" <h3>Hello JSP</h3>\r\n");
out.write("</body>\r\n");
out.write("</html>\r\n");
} catch (Throwable t) {
if (!(t instanceof 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);
}
}
}
从编译之后的JSP源代码中可以看出，我们自己写的JSP文件，编译之后会继承自HttpJspBase类，并且实现JspSourceDependent、JspSourceImports两个接口。
其中HttpJspBean类，它是继承自HttpServlet类，如下图所示：
从这就再次说明了，JSP程序本质上就是一个Servlet程序，因为最终都是继承HttpServlet类的。既然JSP是Servlet，那么就会有service方法啦，JSP中不叫做service方法，而是叫做_jspService()方法，如下所示：
_jspService()方法中，可以看到JSP中编写的那些HTML内容，这些内容采用out.write()方法，嵌入到编译之后的Servlet程序里面。
