Retrotranslator

Contents

1. What is Retrotranslator?
2. What Java 5.0 features are supported?
3. How to use Retrotranslator from the command line?
4. How to use Retrotranslator from Apache Ant or Maven?
5. How to use Retrotranslator from IntelliJ IDEA?
6. How to produce a jar file compatible with Java 1.4?
7. How to use annotations and generics at runtime on Android?
8. How to use Just-in-Time Retrotranslator?
9. What API is supported on Java 1.4 and Java 1.3?
10. How to write an extension?
11. What are the limitations?
12. Alternative tools
13. Contact
14. License

What is Retrotranslator?

Retrotranslator is a tool that makes Java applications compatible with Java 1.4, Java 1.3 and other environments. It supports all Java 5.0 language features and a significant part of the Java 5.0 API on both J2SE 1.4 and J2SE 1.3. In other Java environments only the Java 5.0 features that don't depend on the new API are supported. Retrotranslator employs the ASM bytecode manipulation framework to transform compiled Java classes and the backport of the Java 5.0 concurrency utilities to emulate the Java 5.0 API.

What Java 5.0 features are supported?

• Generics
• Annotations
• Reflection on generics and annotations
• Typesafe enums
• Autoboxing/unboxing
• Enhanced for loop
• Varargs
• Covariant return types
• Formatted output
• Static import
• Concurrency utilities
• Collections framework enhancements

How to use Retrotranslator from the 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 Java 5.0 or Java 6 and put them into some directory, e.g. myclasses.
3. Go to the unzipped directory and execute:
   java -jar retrotranslator-transformer-n.n.n.jar -srcdir myclasses
   Use appropriate options to verify the result and for troubleshooting, e.g. -verify, -classpath, -advanced, and -smart.
4. Put retrotranslator-runtime-n.n.n.jar and backport-util-concurrent-n.n.jar into the classpath of your application if you use the Java 5.0 API.
5. Run or debug the application as usual on Java 1.4.

The 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>

How to use Retrotranslator from Apache Ant or Maven?

The distribution contains an Apache Ant task net.sf.retrotranslator.transformer.RetrotranslatorTask. Every command line option can be set using the corresponding attribute. In addition the source files can be specified with nested fileset, jarfileset, and dirset elements and the classpath can be set with nested classpath elements or the classpathref attribute. The source directories specified with srcdir, dirset, and the dir attribute of fileset should contain the root package of the classes. In case of warnings the build fails unless the value of the failonwarning attribute is set to false. The following script can be used to build one jar compatible with Java 1.4 and another one compatible with Java 1.3.

    <taskdef name="retrotranslator" classname="net.sf.retrotranslator.transformer.RetrotranslatorTask">
        <classpath>
            <fileset dir="../Retrotranslator-n.n.n-bin">
                <include name="retrotranslator-transformer-n.n.n.jar" />
                <include name="retrotranslator-runtime-n.n.n.jar" />
                <include name="backport-util-concurrent-n.n.jar" />
            </fileset>
        </classpath>
    </taskdef>
    
    <retrotranslator target="1.4" destjar="build/application14.jar"
                     smart="true" verify="true" failonwarning="false">
        <fileset dir="build/classes" includes="**/*.class" />
        <jarfileset dir="build/lib" includes="**/*.jar" />
        <classpath>
            <fileset dir="../j2sdk1.4.2_17/jre/lib" includes="**/*.jar"/>
            <fileset dir="../Retrotranslator-n.n.n-bin">
                <include name="retrotranslator-runtime-n.n.n.jar" />
                <include name="backport-util-concurrent-n.n.jar" />
            </fileset>
            <fileset dir="lib" includes="**/*.jar"/>
        </classpath>
    </retrotranslator>

    <retrotranslator target="1.3" destjar="build/application13.jar"
                     smart="true" verify="true" failonwarning="false">
        <fileset dir="build/classes" includes="**/*.class" />
        <jarfileset dir="build/lib" includes="**/*.jar" />
        <classpath>
            <fileset dir="../jdk1.3.1_20/jre/lib" includes="**/*.jar"/>
            <fileset dir="../Retrotranslator-n.n.n-bin">
                <include name="retrotranslator-runtime13-n.n.n.jar" />
                <include name="backport-util-concurrent-java12-n.n.jar" />
            </fileset>
            <fileset dir="lib" includes="**/*.jar"/>
        </classpath>
    </retrotranslator>

Maven users can use the Retrotranslator plugin from the Mojo Project.

How to use Retrotranslator from IntelliJ IDEA?

There is a plugin to automatically translate and verify classes compiled by IntelliJ IDEA, so you can develop in Java 5.0 but run and debug on Java 1.4.

How to produce a jar file compatible with Java 1.4?

If you have a myapplication5.jar file built with Java 5.0 you can use the following command to produce myapplication4.jar. The jar file will be compatible with Java 1.4 and independent of Retrotranslator because backport 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

Also it is recommended to specify the classpath, verify, and smart options. In case of verification failure try the support option.

How to use annotations and generics at runtime on Android?

The Android SDK m5-rc15 does not support generics and annotations at runtime. This issue can be fixed if both classes that read generics or annotations and classes containing them are processed with Retrotranslator. When using Apache Ant add a target like the following one to the build.xml file created by the activityCreator script and make the dex target depend on it.

    <target name="translate" depends="compile">
        <taskdef name="retrotranslator" classname="net.sf.retrotranslator.transformer.RetrotranslatorTask">
            <classpath>
                <fileset dir="../Retrotranslator-n.n.n-bin">
                  <include name="retrotranslator-transformer-n.n.n.jar"/>
                  <include name="retrotranslator-android-n.n.n.jar"/>
                  <include name="retrotranslator-runtime-n.n.n.jar"/>
                  <include name="backport-util-concurrent-n.n.jar"/>
                </fileset>
            </classpath>
        </taskdef>
        <retrotranslator srcdir="${outdir-classes}" target="1.5" reflection="safe" stripannot="true" embed="."/>
    </target>

If you're using the ADT plugin in the Eclipse IDE you cannot run Retrotranslator on your code, but the dependencies of your application can be translated manually before adding them to the Eclipse project.

java -jar retrotranslator-transformer-n.n.n.jar -srcjar mylibrary.jar -destjar mylibrary-android.jar -target 1.5 -reflection safe -stripannot -classpath retrotranslator-android-n.n.n.jar

If any part of your application declares or analyzes annotations you can extract it into a separate library that should be processed with Retrotranslator and added to the main project. Note that you also have to add the retrotranslator-android-n.n.n.jar to the project since the translated libraries depend on it.

How to use Just-in-Time Retrotranslator?

In order to run a Java 5.0 application on Java 1.4 start it with JIT Retrotranslator:

• java -cp retrotranslator-transformer-n.n.n.jar net.sf.retrotranslator.transformer.JITRetrotranslator <options> -jar <jarfile> [<args...>]
• java -cp retrotranslator-transformer-n.n.n.jar:<classpath> net.sf.retrotranslator.transformer.JITRetrotranslator <options> <class> [<args...>]

The options include support, advanced, smart, backport, syncvolatile, syncfinal, and keepclasslit. When running on J2SE 5.0 JIT Retrotranslator simply calls the application, but on J2SE 1.4 it also translates classes compiled for Java 5.0 or later. However this capability depends on the current JVM and the application itself, so under certain conditions JIT Retrotranslator may be unable to translate either a jar file or classes from the classpath or both.

What API is supported on Java 1.4 and Java 1.3?

¹ Supported via the Backport of JSR 166.
² In most cases this type is being replaced with its base type.
³ Supported only when the corresponding feature is enabled via the support or advanced options.
⁴ Introduced in Java 6.
⁵ Not supported on J2SE 1.3.
⁶ Introduced in Java 1.4 and supported on J2SE 1.3.

How to write an extension?

In order to support the API unavailable on the target platform Retrotranslator should be able to replace all references to new classes, constructors, methods, and fields with references to backports compatible with the platform. The location of the backports must be specified with the classpath option. The default backports for the 1.4 target have been packaged into the retrotranslator-runtime-n.n.n.jar and backport-util-concurrent-n.n.jar files, and to complement or override them additional backport names can be specified via the backport option or a properties file. The backport names can have five different forms, the first one declares a universal backport package and the others allow reusing existing backports.

The names of backport classes in a universal backport package consist of the backport package name, the name of the original class, and an optional trailing underscore. For example, net.sf.retrotranslator.runtime.java.util.EnumSet_ is a complete backport of java.util.EnumSet. But when classes exist on the target platform then the backports of their new fields, constructors and methods are grouped into classes with a leading underscore in their names. Look at the net.sf.retrotranslator.runtime.java.math._BigDecimal class:

• 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 and returns an argument for a Java 1.4 constructor.

The net.sf.retrotranslator.runtime.java.io._PrintStream and net.sf.retrotranslator.runtime.java.lang._SecurityException classes use another type of constructor backports. There is a public static createInstanceBuilder method that accepts constructor's arguments an returns an object with public argument1...argumentN methods and an optional public void initialize method. All the argumentX methods don't have any parameters and provide arguments for a constructor that exists on the target platform. The initialize method has a single parameter for the created instance and can be used for postprocessing. And the most flexible but unsupported in certain cases way has been used by net.sf.retrotranslator.runtime.java.lang._StackTraceElement.

If backported methods require access to non-public methods or fields of the instance, they can do it with reflection when the security manager allows such access. The backports of public instance fields are not supported, but private instance fields can be emulated using a weak identity map, see net.sf.retrotranslator.runtime.java.lang._Thread for an example.

What are the limitations?

• The Java 5.0 memory model is not fully supported even with the syncvolatile and syncfinal options if the fields are being accessed via reflection.
• Only the classes, methods, and fields listed above should work and the other features, like formatted input, are not supported.
• The Java 1.4 compilers and applications performing bean introspection may fail to work correctly with covariant return types.
• The backported implementation of the Java 5.0 API is not interoperable with the original implementation.
• Reflection-based tools may be unable to discover the backported implementation of the Java 5.0 API.
• The Java 5.0 reflection methods may return incomplete information for dynamically generated classes.
• The constants inlined by a compiler and access modifiers are ignored during the verification.

Alternative tools

• Retroweaver
• Declawer
• JBossRetro

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License

    Copyright (c) 2005 - 2008 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:
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       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.

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