Java Card Converter: unsupported class file format of version 50.0

Question

I am attempting to generate a CAP file and an export file from the Wallet.java which comes standard in the Java Card SDK under the samples directory. I compile the class, use the converter and encounter the following:

$ javac -g -d classes/ src/com/sun/javacard/samples/wallet/Wallet.java
$ converter -debug -verbose -classdir "$JC_HOME/samples/src" com.sun.javacard.samples.wallet 0xa0:0x0:0x0:0x0:0x62:0x3:0x1:0xc:0x6:0x1 1.0

Java Card 2.2.2 Class File Converter, Version 1.3
Copyright 2005 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.

parsing /home/user/javacard/java_card_kit-2_2_2/samples/src/com/sun/javacard/samples/wallet/Wallet.class
error: com.sun.javacard.samples.wallet.Wallet: unsupported class file format of version 50.0.

conversion completed with 1 errors and 0 warnings.

My Java version and javac versions are the same, Java 1.6:

$ java -version
java version "1.6.0_45"
Java(TM) SE Runtime Environment (build 1.6.0_45-b06)
Java HotSpot(TM) 64-Bit Server VM (build 20.45-b01, mixed mode)
$ javac -version
javac 1.6.0_45

I am using JC SDK 2.2.2 on Ubuntu 14.04. The version of the converter is 1.3:

$ converter -version
Java Card 2.2.2 Class File Converter, Version 1.3
Copyright 2005 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.

I cannot seem to resolve this "unsupported class file format of version 50.0" error. I am slightly puzzled as to why I am encountering this error given Java 1.6 is version 50.0.

Has anyone else encountered the same issue?

Papilla

You must use Java 1.3 to compile your .java files to .class files. Because JCDK2.2.2 converter supports Java 1.3 generated class files only. – Cultivar

@Abraham, Thanks. I will give this a try. – Papilla

Answer 1

The Java Card 2.2.2 converter supports at most the Java 5 class file format (hence it tells you that Java 6/version 50.0 is not supported). Thus, you need to specify the source compatibility/class file version when compiling the source code using newer JDK versions:

javac -g -source 1.5 -target 1.5 -d classes/ src/com/sun/javacard/samples/wallet/Wallet.java

Similarly, for Java Card 2.2.1, you would use version 1.2:

javac -g -source 1.2 -target 1.2 -d classes/ src/com/sun/javacard/samples/wallet/Wallet.java

And for Java Card 2.1.1 (JC SDK 2.1.2), you would use version 1.1:

javac -g -source 1.1 -target 1.1 -d classes/ src/com/sun/javacard/samples/wallet/Wallet.java

You can check the version of a class file with the Java class file disassembler (thanks to @cmanning for mentioning this):

javap -v -cp classes/ com.sun.javacard.samples.wallet.Wallet |grep 'version'

Heterotypic

Thanks, I have already tried that and I still encounter the same result. The outcome of the javac command with the source and target specified still generates a class file with the version 50.0 format. I checked by using the following command javap -verbose src.com.sun.javacard.samples.wallet.Wallet | grep version – Papilla

@Papilla That's odd. This works fine for me with Oracle JDK 8 (1.8.0_60) on Windows 7 as well as with Oracle JDK 6 (1.6.0_30) on Ubuntu 14.04.3 LTS. – Heterotypic

I think there is something wrong with my Ubuntu VM. I created a new VM and was able to control the major version through the javac source and target tags. I think I am on the right track now. Thanks for your help. – Papilla

Dear Michael, I receive javac: invalid source release: 1.1 error, for -source 1.1 -target 1.1 . Why? (Other releases worked fine). – Cultivar

@Abraham Seems as if the depreciated 1.1 is no longer available in Java 7 and Java 8. I have not tested this but using -source 1.2 -target 1.1 should work fine in that case. – Heterotypic

Answer 2

You might want to look into ant-javacard that does such things (as compiler flags depending on JC SDK version) automagically. (disclaimer: i did it)

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