Retrotranslator

What is Retrotranslator?
What Java 5 features are supported?
How to use Retrotranslator from a command line?
How to produce a JAR file compatible with J2SE 1.4?
How to use Retrotranslator from Apache Ant or Maven?
How to use Retrotranslator from IntelliJ IDEA?
How to use Just-in-Time Retrotranslator?
What API is supported on J2SE 1.4?
How to write an extension?
What are the limitations?
Alternative tools
Contact
License

What is Retrotranslator?

Retrotranslator is a tool that makes Java applications compatible with various versions of the Java platform. It supports all Java 5 language features and a significant part of Java 5 API on J2SE 1.4. In other Java environments only the Java 5 language features that does not require new API are supported. Retrotranslator is based on the ASM bytecode manipulation framework and the backport of concurrency utilities.

What Java 5 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 a command line?

Download and unzip the binary distribution file Retrotranslator-n.n.n-bin.zip, where n.n.n is the latest Retrotranslator release number.
Compile your classes with Java 5 or later and put them into some directory, e.g. myclasses.
Go to the unzipped directory and execute:
java -jar retrotranslator-transformer-n.n.n.jar -srcdir myclasses
If you use Java 5 API put retrotranslator-runtime-n.n.n.jar and backport-util-concurrent-n.n.jar into the classpath of your application.
Run or debug the application as usual on J2SE 1.4.x.

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>

Option	Description	Default
`-srcdir <path>`	The directory with the files to process (may be specified several times).	-
`-srcjar <file>`	The JAR archive file with the files to process (may be specified several times).	-
`-destdir <path>`	The directory to place processed files.	The source directory.
`-destjar <file>`	The JAR archive file to place processed files.	The source JAR file.
`-srcmask <mask>`	The wildcard pattern specifying the files to transform rather than copy (classes or UTF-8 text files), e.g. `.class;?.tld`.	`*.class`
`-target <version>`	The version of the JVM where classes should be able to run. The supported targets are 1.1, 1.2, 1.3, 1.4, and 1.5. While API support is available only for the 1.4 target, user-defined backport classes may be used for other targets as well.	`1.4`
`-classpath <path>`	The dependencies of the translated classes, including the target JVM and Retrotranslator itself. The following files should be specified among others if the target is Sun JRE 1.4: `rt.jar`, `jce.jar`, `jsse.jar`, `retrotranslator-runtime-n.n.n.jar`, and `backport-util-concurrent-n.n.jar`. This option may be omitted if the current Java environment matches the target one.	The current classpath.
`-verify`	Asks the translator to examine translated bytecode for references to classes, methods, or fields that cannot be found in the classpath.	`false`
`-support <features>`	Enables advanced features. The names specified should be separated with semicolons, e.g. `ThreadLocal.remove;BigDecimal.setScale`.	-
`-advanced`	Enables all advanced features at once, but it's recommended to enable only required features in order to avoid compatibility issues.	`false`
`-smart`	Makes all backport classes inheritable provided that the classpath correctly reflects the target environment. For example, the backport of the `Writer.append(String)` method may be used to translate the following expression: `new FileWriter("file.tmp").append("Hello")`.	`false`
`-backport <names>`	The backport names separated with semicolons, e.g. `com.myco.all;java.util:com.myco.ju;javax.net.SocketFactory:com.myco.jsse.Factory`. The corresponding backport classes must be present in the classpath.	-
`-embed <package>`	The package name for a partial copy of `retrotranslator-runtime-n.n.n.jar` and `backport-util-concurrent-n.n.jar` to be put along with translated classes. This makes an application independent of other versions of Retrotranslator present in the classpath.	-
`-lazy`	Asks the translator to transform and verify only the classes compiled with a target greater than the current one.	`false`
`-stripsign`	Asks the translator to strip signature (generics) information.	`false`
`-verbose`	Asks the translator for verbose output.	`false`
`-retainapi`	Asks the translator to modify classes for JVM compatibility but keep use of API unless the backport option is specified. Any references introduced by a compiler remain unchanged, like the use of `java.lang.StringBuilder` for string concatenation or the implicit `valueOf` method calls for autoboxing.	`false`
`-retainflags`	Asks the translator to keep Java 5 specific access modifiers.	`false`
`-uptodatecheck`	Asks the translator to skip processing of files if the destination files are newer.	`false`

How to produce a JAR file compatible with J2SE 1.4?

If you have myapplication5.jar file built with Java 5 you can use the following command to produce myapplication4.jar. It 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 and verify options. In case of verification failure try the smart and advanced 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. 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" failonwarning="false">
        <fileset dir="build/classes15" includes="**/*.class">
        <jarfileset dir="build/lib15" includes="**/*.jar">
        <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?

There is a plugin to automatically translate and verify classes compiled by IntelliJ IDEA, so you can develop in Java 5 but run and debug on JRE 1.4.

How to use Just-in-Time Retrotranslator?

In order to run a Java 5 application on J2SE 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 can include support, advanced, smart, and backport. 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 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 J2SE 1.4?

Package	Class	Methods and fields	Compatibility notes
`java.io`	`Closeable²`	* (all methods)
	`Flushable²`	*
	`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`	* (1 new method)
	`Writer`	* (3 new methods)
`java.lang`	`Appendable²`	*
	`Boolean`	* (2 new methods)
	`Byte`	* (1 new method)
	`Character`	* (44 new methods)	New members of `Character.UnicodeBlock` are not supported. All supplementary code points are considered as unassigned.
	`Class`	* (21 new methods)	Enable features "`Class.getMethod`" and "`Class.getDeclaredMethod`" for more uniform support of generics and covariant return types on different platforms³.
	`Deprecated`	*
	`Double`	`valueOf(double)`
	`Enum`	*
	`Float`	`valueOf(float)`
	`IllegalArgumentException`	* (2 new constructors)
	`IllegalStateException`	* (2 new constructors)
	`Integer`	`valueOf(int), signum(int)`
	`Iterable²`	*
	`Long`	`valueOf(long), signum(long)`
	`Package`	* (4 new methods)
	`Readable²`	*
	`Short`	* (2 new methods)
	`StackTraceElement`	* (1 new constructor)
	`String`	* (10 new methods and constructors) `isEmpty()⁴`
	`StringBuffer`	* (11 new methods and constructors)	Enable feature "`StringBuffer.trimToSize`" to use an empty implementation of the `StringBuffer.trimToSize()` method³.
	`StringBuilder`	*	`StringBuilder` is replaced with `StringBuffer`.
	`SuppressWarnings`	*
	`System`	`nanoTime()¹, clearProperty(String)`	The `System.nanoTime()` method precision may vary on different platforms.
	`Thread`	* (8 new methods)	The `Thread.getId()` method does not reflect the order in which threads are created. The `Thread.getStackTrace()` and `Thread.getAllStackTraces()` methods return non-empty stack trace only for the current thread. Enable feature "`Thread.getState`" to support the `Thread.getState()` method, but it may be able to detect only `NEW`, `RUNNABLE` and `TERMINATED` states.³ Enable features "`Thread.setUncaughtExceptionHandler`" and "`Thread.setDefaultUncaughtExceptionHandler`" to support exception handlers for threads created by translated code (in contrast to J2SE 5.0 the default `UncaughtExceptionHandler` takes precedence over `ThreadGroup`)³.
	`Thread.State`	*
	`Thread.UncaughtExceptionHandler²`	*
	`ThreadLocal`	* (1 new method)	Enable feature "`ThreadLocal.remove`" to use alternative `ThreadLocal` and `InheritableThreadLocal` implementations with method `remove()`³.
	`TypeNotPresentException`	*
`java.lang.annotation`	* (all classes)	*
`java.lang.instrument`	*	*	Bytecode instrumentation is not implemented.
`java.lang.management`	`ManagementFactory`	`getPlatformMBeanServer()`	The `ManagementFactory.getPlatformMBeanServer()` method simply returns the first registered `MBeanServer` or creates it when no one exists. An implementation of JMX 1.2 must be present in a classpath.
`java.lang.ref`	`SoftReference`	*	Enable feature "`SoftReference.NullReferenceQueue`" to support `null` for the second parameter of `SoftReference(Object,ReferenceQueue)` on all platforms³.
`java.lang.ref`	`WeakReference`	*	Enable feature "`WeakReference.NullReferenceQueue`" to support `null` for the second parameter of `WeakReference(Object,ReferenceQueue)` on all platforms³.
`java.lang.reflect`	`AccessibleObject`	* (4 new methods)
	`AnnotatedElement²`	*
	`Constructor`	* (11 new methods)
	`Field`	* (8 new methods)
	`GenericArrayType`	*
	`GenericDeclaration²`	*
	`GenericSignatureFormatError`	*
	`MalformedParameterizedTypeException`	*
	`Method`	* (14 new methods)
	`ParameterizedType`	*
	`Type²`	*
	`TypeVariable`	*
	`WildcardType`	*
`java.math`	`BigDecimal`	`ZERO, ONE, TEN, BigDecimal(int), BigDecimal(long), BigDecimal(char[]), BigDecimal(char[], int, int), divideAndRemainder(BigDecimal), divideToIntegralValue(BigDecimal), pow(int), remainder(BigDecimal), toPlainString(), valueOf(double), valueOf(long)`	Enable feature "`BigDecimal.setScale`" to support negative scales in method `BigDecimal.setScale(int, int)`³.
`java.math`	`BigInteger`	`TEN`
`java.net`	`HttpURLConnection`	* (6 new methods)	Enable features "`HttpURLConnection.setChunkedStreamingMode`", "`HttpURLConnection.setFixedLengthStreamingMode`" to use the corresponding methods, but on Java 1.4 they will simply return. Consider using alternative or writing own protocol handlers.
	`Proxy`	*
	`ProxySelector`	*
	`URL`	* (2 new methods)	The `Proxy` is ignored by the `URL.openConnection(Proxy)` method.
	`URLConnection`	* (4 new methods)	Enable features "`URLConnection.getConnectTimeout`", "`URLConnection.setConnectTimeout`", "`URLConnection.getReadTimeout`", "`URLConnection.setReadTimeout`" to use the corresponding methods, but on Java 1.4 they will simply return. Consider using alternative or writing own protocol handlers.
`java.nio`	`CharBuffer`	* (4 new methods)
`java.nio`	`Charset`	* (1 new method)	The `Charset.defaultCharset()` method returns UTF-8 if the default charset is unavailable (occurs on JDK 1.4.0).
`java.rmi.server`	`RemoteObjectInvocationHandler`	*
`java.text`	`DecimalFormat`	* (2 new methods)	Enable feature "`DecimalFormat.setParseBigDecimal`" to support the `DecimalFormat.setParseBigDecimal(boolean)` method, but parsing and formatting precision will still be limited by the `java.lang.Double` or `java.lang.Long` precision³.
`java.util`	`AbstractQueue¹`	*
	`ArrayDeque^1,4`	*
	`Arrays`	* (21 new methods) `copyOf(...)`⁴ (10 methods) `copyOfRange(...)`⁴ (10 methods)
	`Collections¹`	* (13 new methods) `newSetFromMap(Map)`⁴
	`Deque^1,2,4`	*
	`EnumMap`	*
	`EnumSet`	*
	`Formatter`	*
	`LinkedList`	* (5 new methods)
	`PriorityQueue¹`	*
	`Properties`	*
	`Queue^1,2`	*
	`Timer`	* (3 new methods and constructors)	Enable feature "`Timer.All`" to use alternative `Timer` and `TimerTask` implementations in order to be able to call `Timer(String)`, `Timer(String, boolean)`, and `Timer.purge()`³.
	`UUID`	*
`java.util.concurrent, java.util.concurrent.atomic, java.util.concurrent.locks`	almost all classes¹	almost all methods	The `LockSupport` class may be unusable due to insufficient performance. The `Condition.awaitNanos(long)` method has little accuracy guarantees.
`java.util.regex`	`Matcher`	`quoteReplacement(String), toMatchResult()`
	`MatchResult²`	*
	`Pattern`	`quote(String)`
`javax.net.ssl`	`HttpsURLConnection`	* (2 new methods)

¹ Supported via the Backport of JSR 166.
² In most cases this type is 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.

How to write an extension?

In order to support API unavailable on the target platform Retrotranslator should be able to replace all references to new clases, 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 may be specified via the backport option. The backport names may have five different forms, the first one declares a universal backport package and the others allow to reuse existing backports.

Backport name form	Example
`<universal backport package name>`	`net.sf.retrotranslator.runtime com.mycompany.backport`
`<original package name>:<backport package name>`	`java.util.concurrent:edu.emory.mathcs.backport.java.util.concurrent com.sun.org.apache.xerces.internal:org.apache.xerces`
`<original class name>:<backport class name>`	`java.lang.StringBuilder:java.lang.StringBuffer java.util.LinkedHashMap:org.apache.commons.collections.map.LinkedMap`
`<original method name>:<backport method name>`	`java.lang.System.nanoTime:edu.emory.mathcs.backport.java.util.concurrent.helpers.Utils.nanoTime`
`<original field name>:<backport field name>`	`java.util.Collections.EMPTY_MAP:edu.emory.mathcs.backport.java.util.Collections.EMPTY_MAP`

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 an returns an argument for a Java 1.4 constuctor.

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 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. If this approach does not work there is another flexible but not always supported one 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?

Retrotranslator does not emulate the Java 5 memory model.
Only the classes, methods, and fields listed above should work and the other features, like formatted input, are not supported.
Java 5 reflection methods should be able to load compiled classes as resources, so for dynamically generated classes they may return incomplete information.
The backported implementation of Java 5 API may be incompatible with the original API implementation when running on J2SE 5.0.
Reflection-based tools may be unable to discover Java 5 API when running on J2SE 1.4.
The constants inlined by a compiler and access modifiers are ignored during the verification.

    Copyright (c) 2005 - 2007 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
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    CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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    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.

Retrotranslator

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