Pack200.IPacker Interface
Definition
Important
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The packer engine applies various transformations to the input JAR file, making the pack stream highly compressible by a compressor such as gzip or zip.
[Android.Runtime.Register("java/util/jar/Pack200$Packer", "", "Java.Util.Jar.Pack200/IPackerInvoker")]
public interface Pack200.IPacker : Android.Runtime.IJavaObject, IDisposable, Java.Interop.IJavaPeerable[<Android.Runtime.Register("java/util/jar/Pack200$Packer", "", "Java.Util.Jar.Pack200/IPackerInvoker")>]
type Pack200.IPacker = interface
interface IJavaObject
interface IDisposable
interface IJavaPeerable- Attributes
- Implements
Remarks
The packer engine applies various transformations to the input JAR file, making the pack stream highly compressible by a compressor such as gzip or zip. An instance of the engine can be obtained using #newPacker.
The high degree of compression is achieved by using a number of techniques described in the JSR 200 specification. Some of the techniques are sorting, re-ordering and co-location of the constant pool.
The pack engine is initialized to an initial state as described by their properties below. The initial state can be manipulated by getting the engine properties (using #properties) and storing the modified properties on the map. The resource files will be passed through with no changes at all. The class files will not contain identical bytes, since the unpacker is free to change minor class file features such as constant pool order. However, the class files will be semantically identical, as specified in <cite>The Java™ Virtual Machine Specification</cite>.
By default, the packer does not change the order of JAR elements. Also, the modification time and deflation hint of each JAR element is passed unchanged. (Any other ZIP-archive information, such as extra attributes giving Unix file permissions, are lost.)
Note that packing and unpacking a JAR will in general alter the bytewise contents of classfiles in the JAR. This means that packing and unpacking will in general invalidate any digital signatures which rely on bytewise images of JAR elements. In order both to sign and to pack a JAR, you must first pack and unpack the JAR to "normalize" it, then compute signatures on the unpacked JAR elements, and finally repack the signed JAR. Both packing steps should use precisely the same options, and the segment limit may also need to be set to "-1", to prevent accidental variation of segment boundaries as class file sizes change slightly.
(Here's why this works: Any reordering the packer does of any classfile structures is idempotent, so the second packing does not change the orderings produced by the first packing. Also, the unpacker is guaranteed by the JSR 200 specification to produce a specific bytewise image for any given transmission ordering of archive elements.)
In order to maintain backward compatibility, the pack file's version is set to accommodate the class files present in the input JAR file. In other words, the pack file version will be the latest, if the class files are the latest and conversely the pack file version will be the oldest if the class file versions are also the oldest. For intermediate class file versions the corresponding pack file version will be used. For example: If the input JAR-files are solely comprised of 1.5 (or lesser) class files, a 1.5 compatible pack file is produced. This will also be the case for archives that have no class files. If the input JAR-files contains a 1.6 class file, then the pack file version will be set to 1.6.
Note: Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.
Added in 1.5.
Java documentation for java.util.jar.Pack200.Packer.
Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.
Fields
| ClassAttributePfx |
When concatenated with a class attribute name, indicates the format of that attribute, using the layout language specified in the JSR 200 specification. |
| CodeAttributePfx |
When concatenated with a code attribute name, indicates the format of that attribute. |
| DeflateHint |
If this property is set to |
| Effort |
If this property is set to a single decimal digit, the packer will use the indicated amount of effort in compressing the archive. |
| Error |
The string "error", a possible value for certain properties. |
| False |
The string "false", a possible value for certain properties. |
| FieldAttributePfx |
When concatenated with a field attribute name, indicates the format of that attribute. |
| Keep |
The string "keep", a possible value for certain properties. |
| KeepFileOrder |
If this property is set to |
| Latest |
The string "latest", a possible value for certain properties. |
| MethodAttributePfx |
When concatenated with a method attribute name, indicates the format of that attribute. |
| ModificationTime |
If this property is set to the special string |
| Pass |
The string "pass", a possible value for certain properties. |
| PassFilePfx |
Indicates that a file should be passed through bytewise, with no compression. |
| Progress |
The unpacker's progress as a percentage, as periodically updated by the unpacker. |
| SegmentLimit |
This property is a numeral giving the estimated target size N (in bytes) of each archive segment. |
| Strip |
The string "strip", a possible value for certain properties. |
| True |
The string "true", a possible value for certain properties. |
| UnknownAttribute |
Indicates the action to take when a class-file containing an unknown attribute is encountered. |
Properties
| Handle |
Gets the JNI value of the underlying Android object. (Inherited from IJavaObject) |
| JniIdentityHashCode |
Returns the value of |
| JniManagedPeerState |
State of the managed peer. (Inherited from IJavaPeerable) |
| JniPeerMembers |
Member access and invocation support. (Inherited from IJavaPeerable) |
| PeerReference |
Returns a JniObjectReference of the wrapped Java object instance. (Inherited from IJavaPeerable) |
Methods
| AddPropertyChangeListener(IPropertyChangeListener) |
Registers a listener for PropertyChange events on the properties map. |
| Disposed() |
Called when the instance has been disposed. (Inherited from IJavaPeerable) |
| DisposeUnlessReferenced() |
If there are no outstanding references to this instance, then
calls |
| Finalized() |
Called when the instance has been finalized. (Inherited from IJavaPeerable) |
| Pack(JarFile, Stream) |
Takes a JarFile and converts it into a Pack200 archive. |
| Pack(JarInputStream, Stream) |
Takes a JarInputStream and converts it into a Pack200 archive. |
| Properties() |
Get the set of this engine's properties. |
| RemovePropertyChangeListener(IPropertyChangeListener) |
Remove a listener for PropertyChange events, added by
the |
| SetJniIdentityHashCode(Int32) |
Set the value returned by |
| SetJniManagedPeerState(JniManagedPeerStates) | (Inherited from IJavaPeerable) |
| SetPeerReference(JniObjectReference) |
Set the value returned by |
| UnregisterFromRuntime() |
Unregister this instance so that the runtime will not return it from future Java.Interop.JniRuntime+JniValueManager.PeekValue invocations. (Inherited from IJavaPeerable) |
Extension Methods
| JavaCast<TResult>(IJavaObject) |
Performs an Android runtime-checked type conversion. |
| JavaCast<TResult>(IJavaObject) | |
| GetJniTypeName(IJavaPeerable) | |
| PackAsync(Pack200+IPacker, JarFile, Stream) | |
| PackAsync(Pack200+IPacker, JarInputStream, Stream) | |