pack200(1) General Commands Manual pack200(1)
pack200 - JAR Packing tool
pack200 [ OPTIONS ] output-file JAR-file
The options may be in any order. The last option on the command line or in a properties file supersedes all previously specified options.
For a discussion of the options, see OPTIONS below.
OPTIONS see OPTIONS below.
output-file name of the output file.
JAR-file name of the input file.
The pack200 tool is a Java application that transforms a JAR file into a compressed pack200 file using the Java gzip compressor. The com-
pressed packed files are highly compressed JARs that can be directly deployed, saving bandwidth and reducing download time.
The pack200 tool uses several options to fine-tune and set the compression engine.
% pack200 myarchive.pack.gz myarchive.jar
In this example, the myarchive.pack.gz is produced, using the default pack200 and gzip settings.
Produces a JAR file by packing the file myarchive.jar, and unpacking it. The resulting file can be used as an input to the jar-
% pack200 --repack myarchive-packed.jar myarchive.jar
% pack200 --repack myarchive.jar
Produces a pack200 file. With this option a suitable compressor must be used, and the target system must also use a corresponding
% pack200 --no-gzip myarchive.pack myarchive.jar
Strips the attributes used for debugging, from the output. These include SourceFile, LineNumberTable, LocalVariableTable and Local-
VariableTypeTable. Removing these attributes reduces the size of both downloads and installations but reduces the usefulness of
The packer will reorder and transmit all elements. Additionally, the packer may remove JAR directory names. This will reduce the
download size; however, certain JAR file optimizations such as indexing, may not work correctly.
The value is the estimated target size N (in bytes) of each archive segment. If a single input file requires more than N bytes, it
will be given its own archive segment. As a special case, a value of -1 will produce a single large segment with all input files,
while a value of 0 will produce one segment for each class. Larger archive segments result in less fragmentation and better compres-
sion, but processing them requires more memory.
The size of each segment is estimated by counting the size of each input file to be transmitted in the segment, along with the size
of its name and other transmitted properties.
The default is 1000000 (a million bytes). This allows input JAR files of moderate size to be transmitted in one segment. It also
puts a limit on memory requirements for packers and unpackers.
A 10MB JAR packed without this limit will typically pack about 10% smaller, but the packer may require a larger Java heap (about ten
times the segment limit).
If the value is set to a single decimal digit, the packer will use the indicated amount of effort in compressing the archive. Level
1 may produce somewhat larger size and faster compression speed, while level 9 will take much longer but may produce better compres-
sion. The special value 0 instructs the packer to copy through the original JAR file directly, with no compression. The JSR 200
standard requires any unpacker to understand this special case as a pass-through of the entire archive.
The default is 5, investing a modest amount of time to produce reasonable compression.
Overrides the default, which preserves the input information, but may cause the transmitted archive to be larger.
The possible values are:
In either case, the packer will set the deflation hint accordingly in the output archive, and will not transmit the individual
deflation hints of archive elements.
Preserve deflation hints observed in the input JAR. (This is the default.)
The possible values are:
The packer will attempt to determine the latest modification time, among all the available entries in the original archive, or
the latest modification time of all the available entries in that segment. This single value will be transmitted as part of
the segment and applied to all the entries in each segment. This can marginally decrease the transmitted size of the archive
at the expense of setting all installed files to a single date.
Preserve modification times observed in the input JAR. (This is the default.)
Indicates that a file should be passed through byte-wise with no compression. By repeating the option, multiple files may be speci-
fied,. There is no pathname transformation, except that the system file separator is replaced by the JAR file separator '/'. The
resulting file names must match exactly as strings with their occurrences in the JAR file. If file is a directory name, all files
under that directory will be passed.
Overrides the default behavior, ie. the classfile containing the unknown attribute will be passed through with the specified action.
The possible values for actions are:
The pack200 operation as a whole will fail, with a suitable explanation.
The attribute will be dropped. Note: removing the VM required attributes may cause Class Loader failures.
Upon encountering this attribute, the entire class will be transmitted as though it is a resource. (This is the default.)
With the above four options, the attribute layout can be specified for a class entity, such as Class attribute, Field attribute,
Method attribute and Code attribute. The attribute-name is the name of the attribute for which the layout or action is being
The possible values for action are:
(some layout string)
The layout language is defined in the JSR 200 specification. For example --class-attribute=SourceFile=RUH.
upon encountering this attribute, the pack200 operation will fail, with a suitable explanation.
upon encountering this attribute, the attribute will be removed from the output. Note: removing the VM required attributes may
cause Class Loader failures.
upon encountering this attribute, the entire class will be transmitted as though it is a resource.
Example --class-attribute=CompilationID=pass, will cause the classfile containing this attribute to be passed through, without
further action by the packer.
A configuration file, containing Java properties to initialize the packer, may be specified on the command line.
% pack200 -f pack.properties myarchive.pack.gz myarchive.jar
% cat pack.properties
# Generic properties for the packer.
# This option will cause the files bearing new attributes to
# be reported as an error rather than passed uncompressed.
# Change the segment limit to be unlimited.
-v --verbose Outputs minimal messages, multiple specification of this option will output more verbose messages.
-q --quiet Quiet operation with no messages.
A log file to output messages.
-Joption Passes option to the Java launcher called by pack200. For example, -J-Xms48m sets the startup memory to 48
megabytes. Although it does not begin with -X, it is not a `standard option' of pack200. It is a common conven-
tion for -J to pass options to the underlying VM executing applications written in Java.
The following exit values are returned:
0 Successful completion.
>0 An error occurred.
unpack200(1), jar(1), jarsigner(1), attributes(5)
For API specification and other related information:
This command should not be confused with pack(1). They are distinctly separate products.
The J2SE API Specification provided with the JDK release is the superseding
authority, in case of discrepancies.
14 July 2004 pack200(1)