classloader in tomcat[转贴加修改]--rosonsandy.htm

这是最详细的对Tomcat4以上版本的解析。

href="http://www.huihoo.com/apache/tomcat/heavyz/SecurityClassLoad.java.html"><SPAN 
style="mso-bidi-font-size: 12.0pt">[</SPAN><SPAN lang=EN-US 
style="mso-bidi-font-size: 12.0pt"><SPAN lang=EN-US>查看代码]</SPAN></SPAN></A> 
</SPAN></P>
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<P class=MsoNormal 
style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: left; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-outline-level: 3" 
align=left><B><SPAN lang=EN-US 
style="FONT-SIZE: 13.5pt; FONT-FAMILY: 宋体; mso-font-kerning: 0pt; mso-bidi-font-family: 宋体">Appendix 
- </SPAN></B><B><SPAN 
style="FONT-SIZE: 13.5pt; FONT-FAMILY: 宋体; mso-font-kerning: 0pt; mso-bidi-font-family: 宋体">参考<SPAN 
lang=EN-US> </SPAN></SPAN></B></P>
<P>
<P class=MsoNormal 
style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: left; mso-pagination: widow-orphan; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto" 
align=left><SPAN lang=EN-US 
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 0pt; mso-bidi-font-family: 宋体">[1] 
http://jakarta.apache.org/tomcat/</SPAN><SPAN 
style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 0pt; mso-bidi-font-family: 宋体">中的<SPAN 
lang=EN-US>Tomcat 4.1.x</SPAN>文档<SPAN lang=EN-US>Class Loader HOW-TO 
</SPAN></SPAN></P>
<P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=2><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">在一个</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">JVM</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">中可能存在多个</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">ClassLoader</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">，每个</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">ClassLoader</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">拥有自己的</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">NameSpace</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">。一个</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">ClassLoader</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">只能拥有一个</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">class</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">对象类型的实例，但是不同的</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">ClassLoader</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">可能拥有相同的</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">class</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">对象实例，这时可能产生致命的问题。如</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">ClassLoaderA</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">，装载了类</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">A</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">的类型实例</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">A1</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">，而</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">ClassLoaderB</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">，也装载了类</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">A</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">的对象实例</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">A2</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">。逻辑上讲</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">A1=A2</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">，但是由于</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">A1</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">和</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">A2</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">来自于不同的</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">ClassLoader</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">，它们实际上是完全不同的，如果</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">A</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">中定义了一个静态变量</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">c</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">，则</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">c</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">在不同的</SPAN><SPAN 
lang=EN-US 
style="COLOR: blue; FONT-FAMILY: Verdana; mso-bidi-font-size: 10.5pt">ClassLoader</SPAN><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana">中的值是不同的。</SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=2><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana"></SPAN></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=2><SPAN 
style="COLOR: blue; FONT-FAMILY: 宋体; mso-hansi-font-family: Verdana; mso-bidi-font-size: 10.5pt; mso-ascii-font-family: Verdana"><STRONG>深入Java2平台安全</STRONG></SPAN></FONT></P><BR>
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<P class=diaryFoot>- 作者： <A 
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