When a program tries to do XML digital signature, the following exception shows up.

C:\Users\licensees>java -version
java version "1.6.0_21"
Java(TM) SE Runtime Environment (build 1.6.0_21-b06)
Java HotSpot(TM) Client VM (build 17.0-b16, mixed mode)

C:\Users\licensees>javac *.java

C:\Users\licensees>java Main
javax.xml.crypto.dsig.TransformException: Couldn't find Canonicalizer for: http://www.w3.org/TR/2001/REC-xml-c14n-20010315: Unknown canonicalizer. No handler installed for URI http://www.w3.org/TR/2001/REC-xml-c14n-20010315
        at org.jcp.xml.dsig.internal.dom.ApacheCanonicalizer.canonicalize(ApacheCanonicalizer.java:85)
        at org.jcp.xml.dsig.internal.dom.ApacheCanonicalizer.canonicalize(ApacheCanonicalizer.java:71)
        at org.jcp.xml.dsig.internal.dom.DOMCanonicalXMLC14NMethod.transform(DOMCanonicalXMLC14NMethod.java:55)
        at org.jcp.xml.dsig.internal.dom.DOMTransform.transform(DOMTransform.java:111)
        at Main.test1(Main.java:32)
        at Main.main(Main.java:23)
Caused by: com.sun.org.apache.xml.internal.security.c14n.InvalidCanonicalizerException: Unknown canonicalizer. No handlerinstalled for URI http://www.w3.org/TR/2001/REC-xml-c14n-20010315
        at com.sun.org.apache.xml.internal.security.c14n.Canonicalizer.<init>(Canonicalizer.java:108)
        at com.sun.org.apache.xml.internal.security.c14n.Canonicalizer.getInstance(Canonicalizer.java:123)
        at org.jcp.xml.dsig.internal.dom.ApacheCanonicalizer.canonicalize(ApacheCanonicalizer.java:79)
        ... 5 more
com.sun.org.apache.xml.internal.security.c14n.InvalidCanonicalizerException: Unknown canonicalizer. No handler installed for URI
http://www.w3.org/TR/2001/REC-xml-c14n-20010315
        at com.sun.org.apache.xml.internal.security.c14n.Canonicalizer.<init>(Canonicalizer.java:108)
        at com.sun.org.apache.xml.internal.security.c14n.Canonicalizer.getInstance(Canonicalizer.java:123)
        at org.jcp.xml.dsig.internal.dom.ApacheCanonicalizer.canonicalize(ApacheCanonicalizer.java:79)
        at org.jcp.xml.dsig.internal.dom.ApacheCanonicalizer.canonicalize(ApacheCanonicalizer.java:71)
        at org.jcp.xml.dsig.internal.dom.DOMCanonicalXMLC14NMethod.transform(DOMCanonicalXMLC14NMethod.java:55)
        at org.jcp.xml.dsig.internal.dom.DOMTransform.transform(DOMTransform.java:111)
        at Main.test1(Main.java:32)
        at Main.main(Main.java:23)
com.sun.org.apache.xml.internal.security.c14n.InvalidCanonicalizerException: Unknown canonicalizer. No handler installed for URI http://www.w3.org/TR/2001/REC-xml-c14n-20010315
        at com.sun.org.apache.xml.internal.security.c14n.Canonicalizer.<init>(Canonicalizer.java:108)
        at com.sun.org.apache.xml.internal.security.c14n.Canonicalizer.getInstance(Canonicalizer.java:123)
        at org.jcp.xml.dsig.internal.dom.ApacheCanonicalizer.canonicalize(ApacheCanonicalizer.java:79)
        at org.jcp.xml.dsig.internal.dom.ApacheCanonicalizer.canonicalize(ApacheCanonicalizer.java:71)
        at org.jcp.xml.dsig.internal.dom.DOMCanonicalXMLC14NMethod.transform(DOMCanonicalXMLC14NMethod.java:55)
        at org.jcp.xml.dsig.internal.dom.DOMTransform.transform(DOMTransform.java:111)
        at Main.test1(Main.java:32)
        at Main.main(Main.java:23)


REPRODUCE:
1. Compile the attached Main.java
2. Set the attached SampleDOM.xml under the directory where Main.class is placed.
3. Invoke "java Main"

FREQUENCY:
This exception always occurs.

NOTE:
This problem does not occur in jdk7.