## 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?

Retrotranslator is a Java bytecode transformer that translates Java classes compiled with JDK 5.0 into classes that can be run on JVM 1.4. It is a free, open-source tool based on the ASM bytecode manipulation framework and concurrency utilities backported to Java 1.4.

#### 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>`

Option | Description | Default
--- | --- | ---
`-srcdir` | Directory with classes compiled using JDK 5.0 (may be specified several times). | -
`-srcjar` | JAR file with classes compiled using JDK 5.0 (may be specified several times). | -
`-destdir` | Directory to place classes compatible with J2SE 1.4. | Location of sources
`-destjar` | JAR file to place classes compatible with J2SE 1.4. | Location of sources
`-stripsign` | Asks the translator to strip signature (generics) information. | Off
`-verbose` | Asks the translator for verbose output. | Off
`-lazy` | Asks the translator to transform only Java 5 classes. | Off
`-advanced` | Allows to override Java 1.4 methods for better Java 5 compatibility. | Off
`-verify` | Asks the translator for warnings when references to unknown classes, methods, or fields are found. | Off
`-classpath` | The classpath to use for verification including `rt.jar`, `jce.jar`, `jsse.jar` (from JRE 1.4), `retrotranslator-runtime-n.n.n.jar`, and `backport-util-concurrent.jar`. | Current classpath
`-srcmask` | Files to translate (either bytecode or UTF-8 text) , e.g. "`*.class;*.tld`". Only three special characters are supported: "`*?;`". | *.class
`-embed` | Package name for a private copy of `retrotranslator-runtime-n.n.n.jar` and `backport-util-concurrent.jar` to be put into `-destdir` or `-destjar`. This makes your application independent of other versions of Retrotranslator present in the classpath. | -
`-retainapi` | Asks the translator to modify classes for JVM 1.4 compatibility but keep use of Java 5 API. References introduced by a compiler will also remain unchanged, like the use of `java.lang.StringBuilder` for string concatenation or the implicit `valueOf` method call for autoboxing. | Off
`-retainflags` | Asks the translator to keep Java 5 specific access modifiers. | Off
`-backport` | Informs the translator about user-defined backport packages. Package names should be separated by semicolons. | -

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:

Attribute | Description | Default
--- | --- | ---
`srcdir` | Directory with classes compiled using JDK 5.0. | -
`srcjar` | JAR file with classes compiled using JDK 5.0. | -
`destdir` | Directory to place classes compatible with J2SE 1.4. | Location of sources
`destjar` | JAR file to place classes compatible with J2SE 1.4. | Location of sources
`stripsign` | Asks the translator to strip signature (generics) information. | Off
`verbose` | Asks the translator for verbose output. | Off
`lazy` | Asks the translator to transform only Java 5 classes. | Off
`advanced` | Allows to override Java 1.4 methods for better Java 5 compatibility. | Off
`verify` | Asks the translator for warnings when references to unknown classes, methods, or fields are found. | Off
`classpath` | The classpath to use for verification including `rt.jar`, `jce.jar`, `jsse.jar` (from JRE 1.4), `retrotranslator-runtime-n.n.n.jar`, and `backport-util-concurrent.jar`. | Current classpath
`srcmask` | Files to translate (either bytecode or UTF-8 text) , e.g. "`*.class;*.tld`". Only three special characters are supported: "`*?;`". | *.class
`embed` | Package name for a private copy of `retrotranslator-runtime-n.n.n.jar` and `backport-util-concurrent.jar` to be put into `-destdir` or `-destjar`. This makes your application independent of other versions of Retrotranslator present in the classpath. | -
`retainapi` | Asks the translator to modify classes for JVM 1.4 compatibility but keep use of Java 5 API. References introduced by a compiler will also remain unchanged, like the use of `java.lang.StringBuilder` for string concatenation or the implicit `valueOf` method call for autoboxing. | Off
`retainflags` | Asks the translator to keep Java 5 specific access modifiers. | Off
`backport` | Informs the translator about user-defined backport packages. Package names should be separated by semicolons. | -
`failonwarning` | Indicates whether the build will fail when there are verification warnings. | On

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?

Package | Class | Methods and fields | Compatibility notes
--- | --- | --- | ---
`java.lang.annotation` | * (all classes) | * (all methods) |
`java.util.concurrent, java.util.concurrent.atomic, java.util.concurrent.locks` | almost all classes | almost all methods | Supported via the Backport of JSR 166. The `Condition.awaitNanos(long)` method is supported with very little accuracy guarantees.
`java.io` | `Closeable` | `*` | `new Closeable[...]` is replaced with `new Object[...]`
`Flushable` | `*` | `new Flushable[...]` is replaced with `new Object[...]`
`PrintStream` | * (11 new methods and constructors) |
`PrintWriter` | * (11 new methods and constructors) | The `PrintWriter.format` and `PrintWriter.printf` methods always flush the output buffer.
`Reader` | `read(CharBuffer)` |
`Writer` | `append(CharSequence), append(CharSequence, int, int), append(char)` |
`java.lang` | `Appendable` | * | `new Appendable[...]` is replaced with `new Object[...]`
`Boolean` | `parseBoolean(String), compareTo(Boolean)` |
`Byte` | `valueOf(byte)` |
`Character` | `valueOf(char)` |
`Class` | * (21 new methods) | `Class.getMethod(String, Class...)` and `Class.getDeclaredMethod(String, Class...)` are intercepted in advanced mode to better support generics and covariant return types on several JVM implementations.
`Deprecated` | * |
`Double` | `valueOf(double)` |
`Enum` | * |
`Float` | `valueOf(float)` |
`IllegalArgumentException` | `IllegalArgumentException(String, Throwable), IllegalArgumentException(Throwable)` |
`IllegalStateException` | `IllegalStateException(String, Throwable), IllegalStateException(Throwable)` |
`Integer` | `valueOf(int), signum(int)` |
`Iterable` | * | `new Iterable[...]` is replaced with `new Object[...]`
`Long` | `valueOf(long), signum(long)` |
`Package` | * (4 new methods) |
`Readable` | * | `new Readable[...]` is replaced with `new Object[...]`
`Short` | `valueOf(short)` |
`String` | `contains(CharSequence), contentEquals(CharSequence), format(Locale, String, Object...), format(String, Object...), replace(CharSequence, CharSequence)` |
`StringBuffer` | `StringBuffer(CharSequence), append(CharSequence), append(CharSequence, int, int), insert(int, CharSequence), insert(int, CharSequence, int, int)` |
`StringBuilder` | All methods supported in `StringBuffer` | `StringBuilder` is replaced with `StringBuffer`
`SuppressWarnings` | * |
`System` | `nanoTime(), clearProperty(String)` | The `System.nanoTime()` method is supported via the Backport of JSR 166 and its precision may vary on different platforms.
`Thread` | `getStackTrace(), getId()` | The `Thread.getStackTrace()` method returns non-empty stack trace only for the current thread. The `Thread.getId()` method does not reflect the order in which threads are created.
`TypeNotPresentException` | * |
`java.lang.reflect` | `AccessibleObject` | * |
`AnnotatedElement` | * | `new AnnotatedElement[...]` is replaced with `new Object[...]`
`Constructor` | * (11 new methods) |
`Field` | * (8 new methods) |
`GenericArrayType` | * |
`GenericDeclaration` | * | `new GenericDeclaration[...]` is replaced with `new Object[...]`
`GenericSignatureFormatError` | * |
`MalformedParameterizedTypeException` | * |
`Method` | * (14 new methods) |
`ParameterizedType` | * |
`Type` | * | `new Type[...]` is replaced with `new Object[...]`
`TypeVariable` | * |
`WildcardType` | * |
`java.math` | `BigDecimal` | `BigDecimal(int), BigDecimal(long), ZERO, ONE, TEN, divideAndRemainder(BigDecimal), divideToIntegralValue(BigDecimal), pow(int), remainder(BigDecimal), toPlainString(), valueOf(double), valueOf(long)` | The `BigDecimal.setScale(int, int)` method supports negative scales in advanced mode.
`java.rmi.server` | `RemoteObjectInvocationHandler` | * |
`java.net` | `URL` | `toURI()` |
`java.util.nio` | `CharBuffer` | `append(CharSequence), append(CharSequence, int, int), append(char), read(CharBuffer)` |
`java.util` | `AbstractQueue` | * | Supported via the Backport of JSR 166.
`Arrays` | * (21 new methods) |
`Collections` | * (13 new methods) | Supported via the Backport of JSR 166.
`EnumMap` | * |
`EnumSet` | * |
`Formatter` | * |
`LinkedList` | * (5 new methods) |
`PriorityQueue` | * | Supported via the Backport of JSR 166.
`Queue` | * | Supported via the Backport of JSR 166. `new Queue[...]` is replaced with `new Object[...]`
`UUID` | * |
`java.util.regex` | `Matcher` | `quoteReplacement(String), toMatchResult()` |
`MatchResult` | * | `new MatchResult[...]` is replaced with `new Object[...]`
`Pattern` | `quote(String)` |

#### 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

- Latest documentation
- 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
        CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
        SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
        INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
        CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
        ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
        THE POSSIBILITY OF SUCH DAMAGE.