- 1. About the decompiler
- Fernflower is the first actually working analytical decompiler for Java and
- probably for a high-level programming language in general. Naturally it is still
- under development, please send your bug reports and improvement suggestions at
- 2. License
- See license_en.txt
- 3. Running from the command line
- java -jar fernflower.jar [-<option>=<value>]* [<source>]+ <destination>
- * means 0 or more times
- + means 1 or more times
- <source>: file or directory with files to be decompiled. Directories are recursively scanned. Allowed file extensions are class, zip and jar.
- Sources prefixed with -e= mean "library" files that won't be decompiled, but taken into account when analysing relationships between
- classes or methods. Especially renaming of identifiers (s. option 'ren') can benefit from information about external classes.
- <destination>: destination directory
- <option>,<value>: command line option with the corresponding value, see 4.
- java -jar fernflower.jar -hes=0 -hdc=0 c:\Temp\binary\ -e=c:\Java\rt.jar c:\Temp\source\
- java -jar fernflower.jar -dgs=1 c:\Temp\binary\library.jar c:\Temp\binary\Boot.class c:\Temp\source\
- 4. Command line options
- With the exception of mpm and urc the value of 1 means the option is activated, 0 - deactivated. Default
- value, if any, is given between parentheses.
- Typically, the following options will be changed by user, if any: hes, hdc, dgs, mpm, ren, urc
- The rest of options can be left as they are: they are aimed at professional reverse engineers.
- rbr (1): hide bridge methods
- rsy (0): hide synthetic class members
- din (1): decompile inner classes
- dc4 (1): collapse 1.4 class references
- das (1): decompile assertions
- hes (1): hide empty super invocation
- hdc (1): hide empty default constructor
- dgs (0): decompile generic signatures
- occ (0): ouput copyright comment
- ner (1): assume return not throwing exceptions
- den (1): decompile enumerations
- rgn (1): remove getClass() invocation, when it is part of a qualified new statement
- bto (1): interpret int 1 as boolean true (workaround to a compiler bug)
- nns (1): allow for not set synthetic attribute (workaround to a compiler bug)
- uto (1): consider nameless types as java.lang.Object (workaround to a compiler architecture flaw)
- udv (1): reconstruct variable names from debug information, if present
- rer (1): remove empty exception ranges
- fdi (1): deinline finally structures
- asc (0): allow only ASCII characters in string literals. All other characters will be encoded using Unicode escapes (JLS 3.3). Default encoding is UTF8.
- mpm (0): maximum allowed processing time per decompiled method, in seconds. 0 means no upper limit.
- ren (0): rename ambiguous (resp. obfuscated) classes and class elements
- urc : full name of user-supplied class implementing IIdentifierRenamer. It is used to determine which
- class identifiers should be renamed and provides new identifier names. For more information
- s. section 5
- The default logging level is INFO. This value can be overwritten by setting the option 'log' as follows:
- log (INFO): possible values TRACE, INFO, WARN, ERROR
- 5. Renaming identifiers
- Some obfuscators give classes and their member elements short, meaningless and above all ambiguous names. Recompiling of such
- code leads to a great number of conflicts. Therefore it is advisable to let the decompiler rename elements in its turn,
- ensuring uniqueness of each identifier.
- Option 'ren' (i.e. -ren=1) activates renaming functionality. Default renaming strategy goes as follows:
- - rename an element if its name is a reserved word or is shorter than 3 characters
- - new names are built according to a simple pattern: (class|method|field)_<consecutive unique number>
- You can overwrite this rules by providing your own implementation of the 4 key methods invoked by the decompiler while renaming. Simply
- pass a class that implements de.fernflower.main.extern.IIdentifierRenamer in the option 'urc' (e.g. -urc=com.mypackage.MyRenamer) to
- Fernflower. The class must be available on the application classpath.
- The meaning of each method should be clear from naming: toBeRenamed determine whether the element will be renamed, while the other three
- provide new names for classes, methods and fields respectively.
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