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From: zyng <xsli2@yahoo.com>
Newsgroups: comp.lang.java.programmer
Subject: the problem for accessing the classes in rt.jar
Date: Mon, 16 Apr 2012 08:47:33 -0700 (PDT)
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Hi,
I have asked the similar question before. Thank you for all your help. The =
issue is still not solved and is very mysterious. By many testing, I have o=
btained new observations. I think I can ask this question in a better way. =
Thank you for your help.

As everybody knows, rt.jar is located in jre/lib/ directory. It is *automat=
ically* loaded into Java runtime platform. My code uses some classes in rt.=
jar. (Whether this is wise or not, this is different issue. Here, I just ho=
pe to solve the classpath issue related to rt.jar.)

To check rt.jar is *automatically* loaded by Java, in ant script compile ta=
rget, I added the option "-verbose". This shows all path of the classes ref=
erenced:
	<target name=3D"compile" depends=3D"prepare">
		<javac srcdir=3D"${src.dir}" destdir=3D"${build.dir}" compiler=3D"modern"=
 fork=3D"yes" debug=3D"on">
			<classpath refid=3D"project.classpath"/>
			<compilerarg value=3D"-Xlint"/>
			<compilerarg value=3D"-verbose"/>
		</javac>
	</target>

The printout shows that indeed all those JAR files inside jre/lib are loade=
d:
 [javac] [search path for class files: /A/B/jdk1.6.0_25/jre/lib/resources.j=
ar,/A/B/jdk1.6.0_25/jre/lib/rt.jar,/A/B/jdk1.6.0_25/jre/lib/sunrsasign.jar =
..

However, I need this to compile successfully:
	<path id=3D"project.classpath">
           <fileset dir=3D"/A/B/java/">
                <include name=3D"jre/lib/rt.jar"/>
           </fileset>
           ...
	</path>

The print out shows
 [javac] [search path for class files: /A/B/jdk1.6.0_25/jre/lib/resources.j=
ar,/A/B/jdk1.6.0_25/jre/lib/rt.jar,/A/B/jdk1.6.0_25/jre/lib/sunrsasign.jar =
.., ...,/A/B/java/jre/lib/rt.jar, ..
(/A/B/java is a solft link to /A/B/jdk1.6.0_25)

To make my story short, my findings is that in order to compile, rt.jar mus=
t shows up twice and the path must be different from the first time by thes=
e observations:
1) this won't compile:
	<path id=3D"project.classpath">
           <fileset dir=3D"/A/B/jdk1.6.0_25/">
                <include name=3D"jre/lib/rt.jar"/>
           </fileset>
           ...
	</path>
 [javac] [search path for class files: /A/B/jdk1.6.0_25/jre/lib/resources.j=
ar,/A/B/jdk1.6.0_25/jre/lib/rt.jar,/A/B/jdk1.6.0_25/jre/lib/sunrsasign.jar =
.., ...,/A/B/jdk1.6.0_25/jre/lib/rt.jar, ..
(the second time rt.jar path is exactly same as the first time, it seems ja=
va didn't bother to re-load rt.jar -- my understanding)
2)this will work(copy rt.jar to rt2.jar before hand):
	<path id=3D"project.classpath">
           <fileset dir=3D"/A/B/jdk1.6.0_25/">
                <include name=3D"jre/lib/rt2.jar"/>
           </fileset>
           ...
	</path>
 [javac] [search path for class files: /A/B/jdk1.6.0_25/jre/lib/resources.j=
ar,/A/B/jdk1.6.0_25/jre/lib/rt.jar,/A/B/jdk1.6.0_25/jre/lib/sunrsasign.jar =
.., ...,/A/B/jdk1.6.0_25/jre/lib/rt2.jar, ..
(java loads rt2.jar, now my code compiles successfully)
3)this will work(copy jre/lib to somewhere else beforehand)
	<path id=3D"project.classpath">
           <fileset dir=3D"/X/Y/">
                <include name=3D"jre/lib/rt.jar"/>
           </fileset>
           ...
	</path>

 [javac] [search path for class files: /A/B/jdk1.6.0_25/jre/lib/resources.j=
ar,/A/B/jdk1.6.0_25/jre/lib/rt.jar,/A/B/jdk1.6.0_25/jre/lib/sunrsasign.jar =
.., ...,/X/Y/jre/lib/rt.jar, ..
(again, the path of the second time referencing rt.jar is different, java t=
hen load rt.jar into the platform and my code compiles successfully)

My feeling is that the first time rt.jar loaded, the classes inside rt.jar =
cannot be accessed by my code. The second time referencing rt.jar, if every=
thing is exactly same as the first reference(including path and the file na=
me), java skips the loading; if there is some difference(different path or =
different file name) comparing to the first reference, java loads this JAR =
into the platform, then my code can compile.

Can you help me understand this? I really hope that in the ant script, rt.j=
ar no need to be referenced.

Thank you very much.=20