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JSP novice

2022-07-25 22:00:00 【Hua Weiyun】

Catalog

JSP brief introduction

jsp The creation of

jsp How to access the

jsp The essence of

jsp The head of the page Instructions

Common properties ：

JSP brief introduction

jsp The full name is java server pages .java The server page of .
jsp The main function of is to replace Servlet Program returns html Page data .
because Servlet Program returns html Page data is a very cumbersome thing , Not conducive to development and maintenance .

jsp The creation of

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jsp How to access the

jsp Page and html equally , It's all stored in web Under the table of contents . Access is also related to html The page is the same .

Such as :web A file in a directory

a.html page ：http://ip:port/ Project path /a.html

b.jsp page ：http://ip:port/ Project path /b.jsp

jsp The essence of

jsp The essence of servlet Program

When we first visited the server ,tomcat Will be able to jsp Translate the page into a java Source file , And compile it into .class The bytecode program of

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Bytecode file is the corresponding java Source file , Open the source file to find

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b_jsp This class inherits HttpJspBase class , We go through idea Find out HttpJspBase Class directly inherits HttpServlet class , So ,jsp Translated java Class indirectly inherits HttpServlet class , So ,jsp In essence Servlet Program

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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, "JSP  Only  GET、POST  or  HEAD.Jasper  It also allows  OPTIONS");      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('\r');      out.write('\n');    String path = request.getContextPath();    String basepath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";      out.write("\r\n");      out.write("<html>\r\n");      out.write("<head>\r\n");      out.write("    <base href=\"");      out.print(basepath );      out.write("\"/>\r\n");      out.write("    <meta charset=\"utf-8\"/>\r\n");      out.write("    <title>Insert title here</title>\r\n");      out.write("</head>\r\n");      out.write("<body>\r\n");      out.write("b.jsp The page of \r\n");      out.write("</body>\r\n");      out.write("</html>");    } 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);    }  }

Observe the translation Servlet The source code can find , The lower layer also uses the output stream to put html The page is returned to the client .

jsp The head of the page Instructions

jsp Of page Instructions can be modified jsp Some important properties of the page , Or act .

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" %>

Common properties ：

language attribute Express jsp What language documents are translated , For the time being, it can only support Java.

contentType attribute Express jsp What is the data type returned , In the source code response.setContentType() Parameter values

pageEncoding attribute At present jsp The character set of the page file itself .

import attribute Follow java The same as in the source code is used to import packages , Guide class . Such as ：

<%@ page import="java.util.Map" %>

autoFlush attribute Set when out When the output stream buffer is full , Whether to automatically refresh the buffer , Default true.

buffer attribute Set up out Size of buffer , The default is 8kb

When we set not to automatically refresh the buffer , And when the buffer setting is relatively small, it will happen jsp overflow , If auto refresh is set, there will be no overflow .( Buffer settings 8kb Is the best comprehensive )

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errorPage attribute Set when jsp An error occurred while the page was running , Automatically jump to the wrong page path

errorPage Indicates the path to automatically jump after an error , This path usually starts with a diagonal bar , He said the request address was http://ip:port/ Project path /, Map to... In the code web Catalog

b.jsp The page is as follows ：

<%@ page language="java"         contentType="text/html; charset=utf-8"         pageEncoding="utf-8"          autoFlush="true"           buffer="8kb"            errorPage="/error500.jsp"    %><%--errorPage Indicates the path to automatically jump after an error , This path usually starts with a diagonal bar ,             He said the request address was http://ip:port/ Project path /,             Map to... In the code web Catalog             --%><%@ page import="java.util.Map"  %><%    String path = request.getContextPath();    String basepath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";%><html><head>    <base href="<%=basepath %>"/>    <meta charset="utf-8"/>    <title>Insert title here</title></head><body><%-- Make a mistake --%><% int i =10/0; %>b.jsp The page of </body></html>

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isErrorPage attribute Set up current jsp Whether the page · Error message page , The default is false, If it is true You can get exception information .