jsp页面中使用声明脚本添加成员变量，成员方法，内部类

一点看法：

        1.在jsp中，每一行标签都是一个参数，传给out.write()方法的参数，而表达式输出，仅仅是输出内容而已
        2.输出脚本里面的内容是作为参数直接放入service方法的out输出流的打印流中的，所以也不用加分号结尾
        3.代码脚本原封不动的加入到service方法的方法体，方便我们操作方法体中的对象以及做我们想做的一些判断等等
 

这是jsp页面的代码

<%@ page import="java.util.Date" %><%--
  Created by IntelliJ IDEA.
  User: Lenovo
  Date: 2021/10/3
  Time: 19:38
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    


<%--
<%!…%>：声明，用来创建类的成员变量和成员方法(类似与类

--%>
<%--声明属性--%>
<%!
    private int number;
    private Date date;
    private String name;
%>
<%--声明方法--%>
<%!
public void hello(){
    System.out.println("我是jsp解析后的类的成员方法！");
}
%>
<%--声明内部类--%>
<%!
   static class T{
       static {
           System.out.println("我是静态内部类的静态代码块！");
       }
   }
%>

然后我们找到tomcat翻译出来的.java文件

public final class test_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent,
                 org.apache.jasper.runtime.JspSourceImports {


    private int number;
    private Date date;
    private String name;


public void hello(){
    System.out.println("我是jsp解析后的类的成员方法！");
}


   static class T{
       static {
           System.out.println("我是静态内部类的静态代码块！");
       }
   }

  private static final jakarta.servlet.jsp.JspFactory _jspxFactory =
          jakarta.servlet.jsp.JspFactory.getDefaultFactory();

  private static java.util.Map _jspx_dependants;

  private static final java.util.Set _jspx_imports_packages;

  private static final java.util.Set _jspx_imports_classes;

  static {
    _jspx_imports_packages = new java.util.HashSet<>();
    _jspx_imports_packages.add("jakarta.servlet");
    _jspx_imports_packages.add("jakarta.servlet.http");
    _jspx_imports_packages.add("jakarta.servlet.jsp");
    _jspx_imports_classes = new java.util.HashSet<>();
    _jspx_imports_classes.add("java.util.Date");
  }

  private volatile jakarta.el.ExpressionFactory _el_expressionfactory;
  private volatile org.apache.tomcat.InstanceManager _jsp_instancemanager;

  public java.util.Map getDependants() {
    return _jspx_dependants;
  }

  public java.util.Set getPackageImports() {
    return _jspx_imports_packages;
  }

  public java.util.Set getClassImports() {
    return _jspx_imports_classes;
  }

  public jakarta.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 jakarta.servlet.http.HttpServletRequest request, final jakarta.servlet.http.HttpServletResponse response)
      throws java.io.IOException, jakarta.servlet.ServletException {

    if (!jakarta.servlet.DispatcherType.ERROR.equals(request.getDispatcherType())) {
      final java.lang.String _jspx_method = request.getMethod();
      if ("OPTIONS".equals(_jspx_method)) {
        response.setHeader("Allow","GET, HEAD, POST, OPTIONS");
        return;
      }
      if (!"GET".equals(_jspx_method) && !"POST".equals(_jspx_method) && !"HEAD".equals(_jspx_method)) {
        response.setHeader("Allow","GET, HEAD, POST, OPTIONS");
        response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, "JSP 只允许 GET、POST 或 HEAD。Jasper 还允许 OPTIONS");
        return;
      }
    }

    final jakarta.servlet.jsp.PageContext pageContext;
    jakarta.servlet.http.HttpSession session = null;
    final jakarta.servlet.ServletContext application;
    final jakarta.servlet.ServletConfig config;
    jakarta.servlet.jsp.JspWriter out = null;
    final java.lang.Object page = this;
    jakarta.servlet.jsp.JspWriter _jspx_out = null;
    jakarta.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\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write("    \r\n");
      out.write("\r\n");
      out.write("\r\n");
      out.write('\r');
      out.write('\n');
      out.write('\r');
      out.write('\n');
      out.write('\r');
      out.write('\n');
      out.write('\r');
      out.write('\n');
      out.write('\r');
      out.write('\n');
      out.write('\r');
      out.write('\n');
      out.write("\r\n");
      out.write("\r\n");
      out.write("\r\n");
    } catch (java.lang.Throwable t) {
      if (!(t instanceof jakarta.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);
    }
  }
}

发现我们在页面中写入的内容都在该类中加载了 

 再测试其他两个脚本，我这里直接混合使用了

<%
    for(int i=1;i<=10;i++){
        //使用输出流，将标签输出给浏览器
%>
你好
<%}%>
<%--
翻译出来的代码段
for(int i=1;i<=10;i++){
        //使用输出流，将标签输出给浏览器

      out.write("\r\n");
      out.write("
你好
\r\n");
}
--%>

需要注意的是，标签不能直接写在java语句中，只能将Java语句拆分成几段脚本 ，让标签直接在body的下面才可以实现混合嵌套