1. Compiler Usage

The J2JS cross-compiler translates Java class files into JavaScript code and assembles reachable code into an assembly. To boost performance, J2JS is incremental by performing dependency checking based on existence/modification times.

It is important to understand that the assembler will ignore all unreachable code. The decision on reachability is based on a static code analysis and a set of entry points: Only those methods are reachable which can be traced back to a method declared as an entry point.

2. Configuration

The J2JS cross-compiler is configured with an xml string. This string can have the following attributes.

Attribute	Description	Required
baseDir	Semicolon- or whitespace-separated list of path entries on which Java class files may be located. A path entry must not contain whitespaces.	No; default is the current directory.
webPage	The path to the web page. The assembler will generate a script include into the web page. The include will be placed between the magic pair of comments <!-- j2js Script --><!-- j2js Script -->.	Yes
targetDir	The directory to which the enhanced web page and the assemblies will be generated.	Yes
classPath	Semicolon- or whitespace-separated list of path entries on which Java class files may be located. A path entry must not contain whitespaces.	Yes
cacheFile	The assembler will maintain a cache of pre-crosscompiled classes. This is the path to the cache. Hint: For troubleshooting, it may sometimes be useful to delete the cache or to use the noCache option.	Yes
onLoad	The signature of a static method which is called after the document has loaded. The method must have no argument or an argument of type 'java.lang.String[]'. In the latter case, the values of the URL query string are passed to the method. Note: The method is automatically added to the set of entry points, see below.	Yes
junkSize	Assemblies are written in junks of the specified size. Must be of the form [0-9]+B or [0-9]+kB.	Yes
compression	Assemblies are kept as small as possibly. For example, no comments are generated. For maximal compression, set generateLineNumbers to false. Compressed assemblies are hard to read by humans. This fact can add an extra layer of obfuscation to your code. Note: Only semantic compression is used. Currently, no file compression algorithm (for example zip) is employed.	No; default is false
generateLineNumbers	If true, then line number information is generated for debugging purposes, for example in stack traces.	No; default is true
entryPoints	Semicolon- or whitespace-separated list of entry points, see the discussion on reachability above. Each item must either be the signature of a method, of a class, or of a package. A class signature equals specifying all method signatures of that class. A package signature equals specifying all classes in that package (but not in sub-packages). The static onLoad method (see above) is automatically added to the list of entry points. Also added to this list are all pre-reachable signatures. Note: Normally you will only add those entrypoints which the static code analyser cannot detect, for example methods called through reflection (this is the case in the TestRunner target).	No; defaults to the empty list.
noCache	If true, no dependency checking based on existence/modification times takes place, and required sources will always be recompile.	No; default is false.
failonerror	Indicates whether the build will continue even if there are compilation errors.	No; default is true.
logFilePattern	The path and pattern for the log file. Supported are all patterns as defined by class java.util.logging.FileHandler.	No; default is to log to standard output.
logLevel	One of SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST.	No; default is INFO

3. Standalone Invokation

The cross-compiler can be invoked directly on the command line, for example

set applCLASSPATH=lib/j2js.jar;lib/bcel.jar
java -cp %applCLASSPATH% j2js.compiler.Compiler conf/helloworld1.xml


Extracted from /projects/j2js-Demos/compile.bat

4. Ant Invokation

    <target name="HelloWorld1">
        <j2js 
            baseDir="${basedir}"
            targetDir="build/site"
            classPath="build/classes; ${j2js-Runtime.dir}/build/classes"
            webPage="src/site/HelloWorld1.html"
            onLoad="j2js.demo.HelloWorld1#main(java.lang.String[])"
            junkSize="30kB"
            compression="true"
            generateLineNumbers="false"
            cacheFile="build/j2js.cache" />
    </target>

Extracted from /projects/j2js-Demos/build.xml

5. About Signatures

Signatures play an important role for the configuration of J2JS.

packageName.className#methodName(type1, ...)

foo.bar#fooBar(int)
    foo.bar#fooBar()
    foo.bar#fooBar(java.lang.String, int)

java.lang.String

java.lang.*

j2js.preTaintedSignatures = \
    java.lang.NullPointerException#<init>(java.lang.String); \
    java.lang.RuntimeException#<init>(java.lang.String); \
    java.lang.Throwable#printStackTrace(); \
    java.lang.Throwable#fillInStackTrace(); \
    java.lang.Throwable#toString(); \
    java.lang.String#init(); \
    java.lang.System#invoke(java.lang.String,java.lang.String); \
    java.lang.Class$AnnotationInvocationHandler#invoke(\
    		java.lang.Object,\
    		java.lang.reflect.Method,java.lang.Object[]); \
    java.lang.reflect.Proxy#invoke(\
    		java.lang.reflect.Proxy,\
    		java.lang.String,java.lang.Object[]); \
    j2js.client.Engine#getEngine();

Extracted from file:/D:/workspace/j2js-Compiler/src/resources/j2js.properties

j2js.taintIfInstantiated = \
    *#handleEvent(*); \
    *#compare(java.lang.Object,java.lang.Object); \
    *#invoke(*)

Extracted from file:/D:/workspace/j2js-Compiler/src/resources/j2js.properties