jsp的执行流程

╰+哭是因爲堅強的太久メ 2022-02-01 21:15 206阅读 0赞

1.在tomcat的web.xml中, 配置了一个JspServlet, 访问路径是\*.jsp. 所有以.jsp结尾的路径都归JspServlet负责. JspServlet帮忙将所有的jsp文件转换为java代码, java代码编译成class, 运行后信息就被输出到了浏览器.

2. 当客户端访问\*.jsp的路径时, 被JspServlet拦下来, 将jsp文件转换为java代码, 然后编译为class文件, 执行, 页面就看到效果了.具体代码见本节最后

3.分析jsp的执行流程, 需要查看服务器的work目录, 当jsp被访问时, 会在当前目录下, 生成对应的java文件和class文件.

访问路径:C:\\Users\\Administrator\\.IntelliJIdea2018.3\\system\\tomcat\\Tomcat\_7\_0\_79\_jsp\\work\\Catalina\\localhost\\01\_hello\_jsp\_war\_exploded\\org\\apache\\jsp

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## 4. jsp的执行流程文字描述: ##

> 客户端访问jsp资源: http://localhost:8080/项目/index.jsp

> 被JspServlet匹配成功, 执行JspServlet

> JspServlet被称之为JSP引擎,JspServlet会查找index.jsp资源文件, 将jsp文件翻译为java文件, 命名为index\_jsp.java

> index\_jsp.java定义了一个类, 叫index\_jsp, 继承了HttpJspBase类, HttpJspBase有继承了HttpServlet. 所以说, jsp本质上就是一个Servlet.

> 在index\_jsp.java中, 并没有直接定义service方法, 而是重写了父类中的\_jspService方法, 这个方法会被父类中的service方法自动调用.

> 其实\_jspService方法中就是将jsp文件中所有的内容转换成了java输出, 结构是out.write();

> index\_jsp.java被编译为index\_jsp.class, 运行后, 页面就看到效果了.

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## 5.常见疑问 ##

**1.为什么称jsp转化的java代码为servlet，并没有直接继承HttpServlet啊？**

答：由代码可知，HttpJspBase继承了HttpServlet，而error500\_jsp.java由继承了HttpJspBase，所以说error500\_jsp.java是一个servlet

**2.error500\_jsp.java中并没有定义service方法，那是如何进行调用的呢？**

答:由代码可知，error500\_jsp.java的父类 (public abstract class HttpJspBase extends HttpServlet implements HttpJspPage)

存在service，init，destroy等方法，还有一个抽象方法\_jspService，无方法体，service方法无法调用本类的抽象方法\_jspService，而

其子类error500\_jsp.java正好重写了父类的\_jspService()，这就导致父类调用\_jspService()方法时，会跑到子类error500\_jsp.java中去调用该重写的方法。

# 有关文件代码 #

# tomcat中的web.xml中关于jsp的设置 #

当客户端访问\*.jsp的路径时, 被JspServlet拦下来, 将jsp文件转换为java代码, 然后编译为class文件, 执行, 页面就看到效果了

<servlet>
        <servlet-name>jsp</servlet-name>
        <servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class>
        <init-param>
            <param-name>fork</param-name>
            <param-value>false</param-value>
        </init-param>
        <init-param>
            <param-name>xpoweredBy</param-name>
            <param-value>false</param-value>
        </init-param>
        <load-on-startup>3</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>jsp</servlet-name>
        <url-pattern>*.jsp</url-pattern>
        <url-pattern>*.jspx</url-pattern>
    </servlet-mapping>

# 通过JspServlet将jsp转化成的servlet #

error500.jsp--->error500\_jsp.java

/*
     * Generated by the Jasper component of Apache Tomcat
     * Version: Apache Tomcat/7.0.79
     * Generated at: 2019-05-09 07:08:40 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.*;
    
    public final class error500_jsp extends org.apache.jasper.runtime.HttpJspBase
        implements org.apache.jasper.runtime.JspSourceDependent {
    
      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 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 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 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");
          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("<h1>500</h1>");
        } 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);
        }
      }
    }

# HttpJspBase的相关代码 #

error500\_jsp extends org.apache.jasper.runtime.HttpJspBase

由代码可知，HttpJspBase继承了HttpServlet，而error500\_jsp.java由继承了HttpJspBase，所以说error500\_jsp.java是一个servlet

package org.apache.jasper.runtime;
    
    import java.io.IOException;
    import javax.servlet.ServletConfig;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.jsp.HttpJspPage;
    import org.apache.jasper.compiler.Localizer;
    
    public abstract class HttpJspBase extends HttpServlet
      implements HttpJspPage
    {
      private static final long serialVersionUID = 1L;
    
      public final void init(ServletConfig config)
        throws ServletException
      {
        super.init(config);
        jspInit();
        _jspInit();
      }
    
      public String getServletInfo()
      {
        return Localizer.getMessage("jsp.engine.info");
      }
    
      public final void destroy()
      {
        jspDestroy();
        _jspDestroy();
      }
    
      public final void service(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
      {
        _jspService(request, response);
      }
    
      public void jspInit()
      {
      }
    
      public void _jspInit()
      {
      }
    
      public void jspDestroy()
      {
      }
    
      protected void _jspDestroy()
      {
      }
    
      public abstract void _jspService(HttpServletRequest paramHttpServletRequest, HttpServletResponse paramHttpServletResponse)
        throws ServletException, IOException;
    }

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