Retrotranslator

Contents

1. What is Retrotranslator?
2. What Java 5 features are supported?
3. How to use Retrotranslator from a command line?
4. How to use Retrotranslator from Apache Ant or Maven?
5. How to use Retrotranslator from IntelliJ IDEA?
6. How to use Just-in-Time Retrotranslator?
7. What Java 5 classes and methods are supported?
8. How to write an extension for Retrotranslator?
9. What are the limitations?
10. Alternative tools
11. Contact
12. License

What is Retrotranslator?

What Java 5 features are supported?

• Generics (generic types)
• Annotations (metadata)
• Reflection on generics and annotations
• Typesafe enums (enumerated types)
• Autoboxing/unboxing
• Enhanced for loop (for-each loop)
• Varargs (variable arguments)
• Covariant return types
• Formatted output
• Static import
• Concurrency utilities
• Collections framework enhancements

How to use Retrotranslator from a command line?

1. Download and unzip the binary distribution file Retrotranslator-n.n.n-bin.zip, where n.n.n is the latest Retrotranslator release number.
2. Compile your classes with JDK 5.0 and put them into some directory, e.g. myclasses.
3. Go to the unzipped directory Retrotranslator-n.n.n-bin and execute:
   java -jar retrotranslator-transformer-n.n.n.jar -srcdir myclasses
4. If you use Java 5 API put retrotranslator-runtime-n.n.n.jar and backport-util-concurrent.jar into the classpath of your application.
5. Run or debug the application as usual on any JVM 1.4, preferably JRE 1.4.2.

The full command line syntax:
java -jar retrotranslator-transformer-n.n.n.jar <options>
or
java -cp retrotranslator-transformer-n.n.n.jar net.sf.retrotranslator.transformer.Retrotranslator <options>

For example, if you have a Java 5 application myapplication5.jar you can use the following command to produce myapplication4.jar that will run on J2SE 1.4 and is independent of Retrotranslator, since required classes are added to the translated application with a different package name:

java -jar retrotranslator-transformer-n.n.n.jar -srcjar myapplication5.jar -destjar myapplication4.jar -embed com.mycompany.internal

How to use Retrotranslator from Apache Ant or Maven?

The distribution contains an integrated Apache Ant task net.sf.retrotranslator.transformer.RetrotranslatorTask. It has the following syntax:

You may use nested src elements to specify source directories or JAR files, and nested classpath elements to specify classpath for verification. For example:

    <path id="classpath">
        <fileset dir="lib" includes="**/*.jar"/>
    </path>
    <taskdef name="retrotranslator" classpathref="classpath"
             classname="net.sf.retrotranslator.transformer.RetrotranslatorTask" />
    <retrotranslator destdir="build/classes14" verify="true">
        <src path="build/classes15"/>
        <classpath location="${java14_home}/jre/lib/rt.jar"/>
        <classpath refid="classpath"/>
    </retrotranslator>

For Maven there is a Retrotranslator plugin from the Mojo Project.

How to use Retrotranslator from IntelliJ IDEA?

To automatically translate and verify classes compiled by IntelliJ IDEA you may download a plugin that generates classes compatible with 1.4 virtual machines from your Java 5 source code.

How to use Just-in-Time Retrotranslator?

JIT Retrotranslator is able to translate at runtime Java classes loaded with any classloader. It works on J2SE 1.4 from Sun, IBM, BEA, and Apple, but does nothing on J2SE 5.0 and other platforms. However translation at runtime consumes additional memory and processing resources and it will not work if your classes make use of Java 5 API but were compiled with "-target 1.4".

• If you want to run a JAR file with the JIT, execute:
  java -cp retrotranslator-transformer-n.n.n.jar net.sf.retrotranslator.transformer.JITRetrotranslator <options> -jar <jarfile> [<args...>]
• When the first option does not work or if you just want to run a class from your classpath, execute:
  java -cp retrotranslator-transformer-n.n.n.jar:<classpath> net.sf.retrotranslator.transformer.JITRetrotranslator <options> <class> [<args...>]
• Alternatively you may simply call JITRetrotranslator.run() from some JVM 1.4 compatible class before Java 5 classes are loaded.

JIT Retrotranslator can accept -advanced and -backport options.

What Java 5 classes and methods are supported?

How to write an extension for Retrotranslator?

Since most backported classes are discovered by Retrotranslator at translation time, you may write an extension and simply put it into the Retrotranslator classpath to make it work. For example, all references to java.util.EnumSet are replaced with references to net.sf.retrotranslator.runtime.java.util.EnumSet_ (trailing underscore) if the latter can be found. But if you replace a whole class that exists in J2SE 1.4 you may encounter interoperability issues with other libraries. So, for example, support for Java 5 fields, methods, and constructors of java.math.BigDecimal is placed into net.sf.retrotranslator.runtime.java.math._BigDecimal (leading underscore):

• For a static field there is a public static field with the same name and type.
• For a static method there is a public static method with the same signature.
• For an instance method there is a public static method with the same signature but with an additional first parameter representing the instance.
• For a constructor there is a public static convertConstructorArguments method that accepts constructor's arguments an returns an argument for a Java 1.4 constuctor.

Another approach for constructor backporting is used by net.sf.retrotranslator.runtime.java.io._PrintStream. There is a public static createInstanceBuilder method that accepts constructor's arguments an returns an object with public argument1...argumentN methods and optional public void initialize method. All argumentX methods provide arguments for a Java 1.4 constuctor and should not have any parameters. The initialize method has a single parameter for the created instance and may be used for postprocessing.

However, if the backported methods require access to non-public methods or fields of the instance, they cannot be fully handled by Retrotranslator. While you can use reflection to access any data, translated code generally should not depend on security settings. For example, it is impossible to write an implementation for methods getSource() and setSource() of java.beans.PropertyEditorSupport that will work in any environment. Also this approach cannot be used to replace instance field references.

You can put your extensions into packages other than net.sf.retrotranslator.runtime. For example, to make Retrotranslator use com.mycompany.internal.java.lang._String just specify -backport com.mycompany.internal at the command line. If you have written an extension that does not contain copyrighted code, you may send a patch under the Retrotranslator license.

What are the limitations?

Basically, only classes, methods, and fields listed above should work, and other features, like formatted input, are not supported. Known issues:

• Reflection-based tools may be unable to discover additional classes and methods introduced in Java 5 when running on JRE 1.4.
• Some applications enable all features only if they detect Java 5, so you may need to override system properties:
   java -Djava.version=1.5.0 -Djava.specification.version=1.5 -Djava.class.version=49.0 ...
• Translated code running on JRE 5.0 may be incompatible with other Java 5 code when Java 5 API is used.
• Reflection on generics and metadata may return incomplete information for dynamically generated classes.
• Constants inlined by a compiler and access modifiers are ignored during the verification.
• Inherited methods introduced in Java 5 may not work, however upcasting may help in some cases:
   ((Writer) new FileWriter("file.tmp")).append("Hello").close();
• Serialized objects produced by translated code may be incompatible with JRE 5.0.

Alternative tools

• Retroweaver - a Java bytecode weaver that enables you to take advantage of the new 1.5 language features in your source code, while still retaining compatibility with 1.4 virtual machines.
• Declawer - a customized Java compiler which reduces 1.5 Generics to equivalent 1.4 syntax.

Contact

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• Open discussion
• Help
• Bugs
• Feature requests
• Author

License

    Retrotranslator: a Java bytecode transformer that translates Java classes
    compiled with JDK 5.0 into classes that can be run on JVM 1.4.

    Copyright (c) 2005, 2006 Taras Puchko
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:
    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in the
       documentation and/or other materials provided with the distribution.
    3. Neither the name of the copyright holders nor the names of its
       contributors may be used to endorse or promote products derived from
       this software without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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    ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
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