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JSP页面中的pageEncoding和contentType两种属性

JSP page指令：

JSP文件：

<%@ page language="java"%>
<%@ page import="java.util.*"%>
<%@ page isThreadSafe="false"%>
<%@ page contentType="text/html; charset=UTF-8"%>
<%@ page isELIgnored="true"%>
<%@ page isErrorPage="true"%>
<%@ page errorPage="index0051.jsp"%>
<!-- %@ page extends="org.apache.jsp"% -->
<%@ page session="false"%>
<%@ page buffer="none"%>
<%@ page autoFlush="true"%>
<%@ page info="infotext"%>
<%@ page pageEncoding="UTF-8"%>
<%
    String path = request.getContextPath();
    String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
    pageContext.setAttribute("pca", "pageContextAttribute");
    //session.setAttribute("s", "session");
%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>005index</title>
</head>
<body>
    <p>Page指令</p>
    <p>Page指令可以在页面内随便放置，最好放在页首；</p>
    <p>language属性不写可以，写成别的会无法编译，异常为:org.apache.jasper.JasperException: /index005.jsp (line: 1, column: 2) Page directive: invalid language attribute</p>
    <%@ page import="a.b.*"%>
    <p>import属性，写了之后会自动添加到servlet的import语句中，但不进行包存在性的检查；反编译生成的class中就没有无效的包；</p>
    <p>isThreadSafe问你的应用是否是线程安全的，缺省为true，表示应用是线程安全的，可以同时响应多个请求；如果设置为false，生成的servlet会实现javax.servlet.SingleThreadModel线程，那么一次只能处理一个用户请求；</p>
    <p>${pageScope.pca }</p>
    <p>isELIgnored忽略el表达式</p>
    <p>errorPage="relativeURL" 设置处理异常事件的JSP文件。 isErrorPage="true | false" 设置此页是否为出错页，如果被设置为true,你就能使用exception对象.</p>
    <p>extends="package.class" 标明JSP编译时需要加入的Java Class的全名，但是得慎重的使用它，它会限制JSP的编译能力.写成别的就无法转换了。org.apache.jasper.JasperException: Unable to compile class for JSP:</p>
    <p>session="false"就没有session对象了；</p>
    <p>contentType属性设置发送到客户端文档的响应报头的MIME类型和字符编码。多个使用;号分开。 pageEncodeing属性只用于更改字符编码。</p>
    <p>buffer属性指定out对象(JspWriter)使用的缓冲区大小，以kb为单位，默认8kb。 none表示不使用缓冲区。这样要求设置报头或状态代码的jsp元素要出现在文件的顶部，任何HTML内容之前。 autoFlush属性控制当缓冲区满了后，是自动清空输出缓冲区(默认true)，还是在缓冲区溢出后抛出异常(false)。
        在buffer=none的时候，autoFlush=false是错误的。</p>
    <p>定义一个可以在servlet中通过getServletInfo方法获取的字符串。 jsp容器做的是在servlet中生成getServletInfo方法返回info属性指定的String。</p>
</body>
</html>

JSP转换的java文件：

/*
 * Generated by the Jasper component of Apache Tomcat
 * Version: Apache Tomcat/7.0.35
 * Generated at: 2015-10-20 00:27:17 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.*;
import a.b.*;

public final class index005_jsp extends org.apache.jasper.runtime.HttpJspBase
    implements org.apache.jasper.runtime.JspSourceDependent,
                 javax.servlet.SingleThreadModel {

  public java.lang.String getServletInfo() {
    return "infotext";
  }

  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 javax.el.ExpressionFactory _el_expressionfactory;
  private org.apache.tomcat.InstanceManager _jsp_instancemanager;

  public java.util.Map<java.lang.String,java.lang.Long> getDependants() {
    return _jspx_dependants;
  }

  public void _jspInit() {
    _el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
    _jsp_instancemanager = org.apache.jasper.runtime.InstanceManagerFactory.getInstanceManager(getServletConfig());
  }

  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;
    java.lang.Throwable exception = org.apache.jasper.runtime.JspRuntimeLibrary.getThrowable(request);
    if (exception != null) {
      response.setStatus(javax.servlet.http.HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
    }
    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,
                  "index0051.jsp", false, 0, true);
      _jspx_page_context = pageContext;
      application = pageContext.getServletContext();
      config = pageContext.getServletConfig();
      out = pageContext.getOut();
      _jspx_out = out;

      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("<!-- %@ page extends="org.apache.jsp"% -->
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");

    String path = request.getContextPath();
    String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
    pageContext.setAttribute("pca", "pageContextAttribute");
    //session.setAttribute("s", "session");

      out.write("
");
      out.write("<!DOCTYPE html>
");
      out.write("<html>
");
      out.write("<head>
");
      out.write("<meta charset="UTF-8">
");
      out.write("<title>005index</title>
");
      out.write("</head>
");
      out.write("<body>
");
      out.write("	<p>Page指令</p>
");
      out.write("	<p>Page指令可以在页面内随便放置，最好放在页首；</p>
");
      out.write("	<p>language属性不写可以，写成别的会无法编译，异常为:org.apache.jasper.JasperException: /index005.jsp (line: 1, column: 2) Page directive: invalid language attribute</p>
");
      out.write("	
");
      out.write("	<p>import属性，写了之后会自动添加到servlet的import语句中，但不进行包存在性的检查；反编译生成的class中就没有无效的包；</p>
");
      out.write("	<p>isThreadSafe问你的应用是否是线程安全的，缺省为true，表示应用是线程安全的，可以同时响应多个请求；如果设置为false，生成的servlet会实现javax.servlet.SingleThreadModel线程，那么一次只能处理一个用户请求；</p>
");
      out.write("	<p>${pageScope.pca }</p>
");
      out.write("	<p>isELIgnored忽略el表达式</p>
");
      out.write("	<p>errorPage="relativeURL" 设置处理异常事件的JSP文件。 isErrorPage="true | false" 设置此页是否为出错页，如果被设置为true,你就能使用exception对象.</p>
");
      out.write("	<p>extends="package.class" 标明JSP编译时需要加入的Java Class的全名，但是得慎重的使用它，它会限制JSP的编译能力.写成别的就无法转换了。org.apache.jasper.JasperException: Unable to compile class for JSP:</p>
");
      out.write("	<p>session="false"就没有session对象了；</p>
");
      out.write("	<p>contentType属性设置发送到客户端文档的响应报头的MIME类型和字符编码。多个使用;号分开。 pageEncodeing属性只用于更改字符编码。</p>
");
      out.write("	<p>buffer属性指定out对象(JspWriter)使用的缓冲区大小，以kb为单位，默认8kb。 none表示不使用缓冲区。这样要求设置报头或状态代码的jsp元素要出现在文件的顶部，任何HTML内容之前。 autoFlush属性控制当缓冲区满了后，是自动清空输出缓冲区(默认true)，还是在缓冲区溢出后抛出异常(false)。
");
      out.write("		在buffer=none的时候，autoFlush=false是错误的。</p>
");
      out.write("	<p>定义一个可以在servlet中通过getServletInfo方法获取的字符串。 jsp容器做的是在servlet中生成getServletInfo方法返回info属性指定的String。</p>
");
      out.write("</body>
");
      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 { 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);
    }
  }
}

反编译class文件：

package org.apache.jsp;

import java.io.IOException;
import java.util.Map;
import javax.el.ExpressionFactory;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.SingleThreadModel;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.jsp.JspApplicationContext;
import javax.servlet.jsp.JspFactory;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.SkipPageException;
import org.apache.jasper.runtime.HttpJspBase;
import org.apache.jasper.runtime.InstanceManagerFactory;
import org.apache.jasper.runtime.JspRuntimeLibrary;
import org.apache.jasper.runtime.JspSourceDependent;
import org.apache.tomcat.InstanceManager;

public final class index005_jsp extends HttpJspBase
  implements JspSourceDependent, SingleThreadModel
{
  private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory();
  private static Map<String, Long> _jspx_dependants;
  private ExpressionFactory _el_expressionfactory;
  private InstanceManager _jsp_instancemanager;

  public String getServletInfo()
  {
    return "infotext";
  }

  public Map<String, Long> getDependants()
  {
    return _jspx_dependants;
  }

  public void _jspInit() {
    this._el_expressionfactory = _jspxFactory.getJspApplicationContext(getServletConfig().getServletContext()).getExpressionFactory();
    this._jsp_instancemanager = InstanceManagerFactory.getInstanceManager(getServletConfig());
  }

  public void _jspDestroy()
  {
  }

  public void _jspService(HttpServletRequest request, HttpServletResponse response)
    throws IOException, ServletException
  {
    Throwable exception = JspRuntimeLibrary.getThrowable(request);
    if (exception != null) {
      response.setStatus(500);
    }

    JspWriter out = null;

    JspWriter _jspx_out = null;
    PageContext _jspx_page_context = null;
    try
    {
      response.setContentType("text/html; charset=UTF-8");
      PageContext pageContext = _jspxFactory.getPageContext(this, request, response, 
        "index0051.jsp", false, 0, true);
      _jspx_page_context = pageContext;
      pageContext.getServletContext();
      pageContext.getServletConfig();
      out = pageContext.getOut();
      _jspx_out = out;

      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("<!-- %@ page extends="org.apache.jsp"% -->
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");
      out.write("
");

      String path = request.getContextPath();
      new StringBuilder(String.valueOf(request.getScheme())).append("://").append(request.getServerName()).append(":").append(request.getServerPort()).append(path).append("/").toString();
      pageContext.setAttribute("pca", "pageContextAttribute");

      out.write("
");
      out.write("<!DOCTYPE html>
");
      out.write("<html>
");
      out.write("<head>
");
      out.write("<meta charset="UTF-8">
");
      out.write("<title>005index</title>
");
      out.write("</head>
");
      out.write("<body>
");
      out.write("	<p>Page指令</p>
");
      out.write("	<p>Page指令可以在页面内随便放置，最好放在页首；</p>
");
      out.write("	<p>language属性不写可以，写成别的会无法编译，异常为:org.apache.jasper.JasperException: /index005.jsp (line: 1, column: 2) Page directive: invalid language attribute</p>
");
      out.write("	
");
      out.write("	<p>import属性，写了之后会自动添加到servlet的import语句中，但不进行包存在性的检查；反编译生成的class中就没有无效的包；</p>
");
      out.write("	<p>isThreadSafe问你的应用是否是线程安全的，缺省为true，表示应用是线程安全的，可以同时响应多个请求；如果设置为false，生成的servlet会实现javax.servlet.SingleThreadModel线程，那么一次只能处理一个用户请求；</p>
");
      out.write("	<p>${pageScope.pca }</p>
");
      out.write("	<p>isELIgnored忽略el表达式</p>
");
      out.write("	<p>errorPage="relativeURL" 设置处理异常事件的JSP文件。 isErrorPage="true | false" 设置此页是否为出错页，如果被设置为true,你就能使用exception对象.</p>
");
      out.write("	<p>extends="package.class" 标明JSP编译时需要加入的Java Class的全名，但是得慎重的使用它，它会限制JSP的编译能力.写成别的就无法转换了。org.apache.jasper.JasperException: Unable to compile class for JSP:</p>
");
      out.write("	<p>session="false"就没有session对象了；</p>
");
      out.write("	<p>contentType属性设置发送到客户端文档的响应报头的MIME类型和字符编码。多个使用;号分开。 pageEncodeing属性只用于更改字符编码。</p>
");
      out.write("	<p>buffer属性指定out对象(JspWriter)使用的缓冲区大小，以kb为单位，默认8kb。 none表示不使用缓冲区。这样要求设置报头或状态代码的jsp元素要出现在文件的顶部，任何HTML内容之前。 autoFlush属性控制当缓冲区满了后，是自动清空输出缓冲区(默认true)，还是在缓冲区溢出后抛出异常(false)。
");
      out.write("		在buffer=none的时候，autoFlush=false是错误的。</p>
");
      out.write("	<p>定义一个可以在servlet中通过getServletInfo方法获取的字符串。 jsp容器做的是在servlet中生成getServletInfo方法返回info属性指定的String。</p>
");
      out.write("</body>
");
      out.write("</html>
");
    } catch (Throwable t) {
      if (!(t instanceof SkipPageException)) {
        out = _jspx_out;
        if ((out != null) && (out.getBufferSize() != 0)) try {
            out.clearBuffer(); } catch (IOException localIOException) { }
        if (_jspx_page_context != null) _jspx_page_context.handlePageException(t);
        else throw new ServletException(t);
      }

      _jspxFactory.releasePageContext(_jspx_page_context); } finally { _jspxFactory.releasePageContext(_jspx_page_context);
    }
  }
}

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原文地址：https://www.cnblogs.com/jinhengyu/p/10258113.html