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From: zyng <xsli2@yahoo.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: the problem for accessing the classes in rt.jar
Date: Wed, 18 Apr 2012 06:13:36 -0700 (PDT)
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OK. And also re-phrase my question:=20
A)in build.xml file, when not including rt.jar by commenting out rt.jar:

        <path id=3D"project.classpath">
            <!--fileset dir=3D"$/A/B/jdk1.6.0_25">
                <include name=3D"jre/lib/rt.jar"/>
            </fileset-->
                <pathelement location=3D"${build.dir}"/>
                <fileset dir=3D"${externals.dir}">
                        <include name=3D"abc.jar"/>
                        <include name=3D"xyz.jar"/>
                        <include name=3D"junit.jar"/>
                </fileset>
        </path>=20


I got these error message

compile:
    [javac] C:\my_work\build.xml:47: warning: 'includeantruntime' was not s=
et, defaulting to build.sysclasspath=3Dlast; set to fals
 for repeatable builds
    [javac] Compiling 407 source files to C:\my_work\build
    [javac] C:\my_work\src\abc\efg\xml\MyXmlUtils.java:27: package com.sun.=
xml.internal.fastinfoset.stax does not exist
    [javac] import com.sun.xml.internal.fastinfoset.stax.StAXDocumentParser=
;
    [javac]                                             ^
    [javac] C:\my_work\src\abc\efg\xml\MyXmlUtils.java:28: package com.sun.=
xml.internal.fastinfoset.stax does not exist
    [javac] import com.sun.xml.internal.fastinfoset.stax.StAXDocumentSerial=
izer;
    [javac]                                             ^
    [javac] C:\my_work\src\abc\efg\xml\MyXmlUtils.java:29: package com.sun.=
xml.internal.txw2.output does not exist
...


Those packages are located inside rt.jar. And everybody agrees, rt.jar is a=
utomatically loaded into the platform. Since I added the option "-verbose" =
in javac, I saw this print out, which clearly shows rt.jar is in the class =
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 =
..=20

Clearly, my code cannot access /jre/lib/rt.jar so compiling failed. Why my =
code cannot access rt.jar?

B)If including rt.jar in the project.classpath:
        <path id=3D"project.classpath">
            <fileset dir=3D"$/A/B/jdk1.6.0_25">
                <include name=3D"jre/lib/rt.jar"/>
            </fileset>
                <pathelement location=3D"${build.dir}"/>
                <fileset dir=3D"${externals.dir}">
                        <include name=3D"abc.jar"/>
                        <include name=3D"xyz.jar"/>
                        <include name=3D"junit.jar"/>
                </fileset>
        </path>=20

I got exactly the same error message. The classpath shown by -verbose is:
 [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 ..

"/A/B/jdk1.6.0_25/jre/lib/rt.jar" shows up twice, which makes sense(one is =
due to automatically loaded, one is due to explicit reference in my build.x=
ml).=20

C)if I make a soft link which points to /A/B/jdk1.6.0_25, with a name, say,=
 "/fs/soft_link" and in project.classpath:
        <path id=3D"project.classpath">
            <fileset dir=3D"$/fs/soft_link">
                <include name=3D"jre/lib/rt.jar"/>
            </fileset>
                <pathelement location=3D"${build.dir}"/>
                <fileset dir=3D"${externals.dir}">
                        <include name=3D"abc.jar"/>
                        <include name=3D"xyz.jar"/>
                        <include name=3D"junit.jar"/>
                </fileset>
        </path>=20
On linux, this will work, because linux does not "translate" the soft link =
back to its original 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 =
.. /fs/soft_link/jre/lib/rt.jar ..

"rt.jar" shows up twice, with different path. JAVA clearly re-loaded rt.jar=
, from /fs/soft_link path and my code now can grap the classes they need.

On PC, it does not work. Somehow, PC "translate" the soft link into its rea=
l path, so again, "/A/B/jdk1.6.0_25/jre/lib/rt.jar" shows up twice. My gues=
s is that JAVA does not do repeated loading. As case A) above showed, the f=
irst time loading of "/A/B/jdk1.6.0_25/jre/lib/rt.jar" does not help my cod=
e.

D)this case works on both Linux and PC. Just for testing purpose only:
within /A/B/jdk1.6.0_25/jre/lib/, copy rt.jar to rt2.jar, in project.classp=
ath:

        <path id=3D"project.classpath">
            <fileset dir=3D"$/A/B/jdk1.6.0_25">
                <include name=3D"jre/lib/rt2.jar"/>
            </fileset>
                <pathelement location=3D"${build.dir}"/>
                <fileset dir=3D"${externals.dir}">
                        <include name=3D"abc.jar"/>
                        <include name=3D"xyz.jar"/>
                        <include name=3D"junit.jar"/>
                </fileset>
        </path>=20
Now compiling is fine.
 [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 ..

Clearly, JAVA loaded rt2.jar since "/A/B/jdk1.6.0_25/jre/lib/rt2.jar" looks=
 different from "/A/B/jdk1.6.0_25/jre/lib/rt.jar", at least in JAVA's view.=
 Now my code have their classes to grab.

E)Needless to say, if copying rt.jar from /A/B/jdk1.6.0_25/jre/lib/ to some=
where else, say, /C/D/jre/lib, now in project.classpath:
        <path id=3D"project.classpath">
            <fileset dir=3D"$/C/D">
                <include name=3D"jre/lib/rt.jar"/>
            </fileset>
                <pathelement location=3D"${build.dir}"/>
                <fileset dir=3D"${externals.dir}">
                        <include name=3D"abc.jar"/>
                        <include name=3D"xyz.jar"/>
                        <include name=3D"junit.jar"/>
                </fileset>
        </path>=20
Compiling is fine.
 [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 =
.. /C/D/jre/lib/rt.jar ..

To summarize what I saw,=20
1)"/A/B/jdk1.6.0_25/jre/lib/rt.jar" will be loaded automatically regardless=
 of including rt.jar in the project.classpath or not. However, this loading=
 do not serve my code.
2)in build.xml, project.classpath, when referencing "rt.jar", it needs eith=
er the path be different or the file name be different, somehow fool JAVA t=
o really re-load this JAR file. Only this second loading of rt.jar can help=
 my code. Very strange!

Thank you very much.

Thank you very much.