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/OpenJDK 21

Class JarInputStream

java.lang.Object
java.io.InputStream
java.io.FilterInputStream
java.util.zip.InflaterInputStream
java.util.zip.ZipInputStream
java.util.jar.JarInputStream
All Implemented Interfaces:
Closeable, AutoCloseable 
public class JarInputStream extends ZipInputStream
The JarInputStream class, which extends ZipInputStream, is used to read the contents of a JAR file from an input stream. It provides support for reading an optional Manifest entry. The Manifest can be used to store meta-information about the JAR file and its entries.

Accessing the Manifest

The getManifest method is used to return the Manifest from the entry META-INF/MANIFEST.MF when it is the first entry in the stream (or the second entry if the first entry in the stream is META-INF/ and the second entry is META-INF/MANIFEST.MF).

The getNextJarEntry() and getNextEntry() methods are used to read JAR file entries from the stream. These methods skip over the Manifest (META-INF/MANIFEST.MF) when it is at the beginning of the stream. In other words, these methods do not return an entry for the Manifest when the Manifest is the first entry in the stream. If the first entry is META-INF/ and the second entry is the Manifest then both are skipped over by these methods. Whether these methods skip over the Manifest when it appears later in the stream is not specified.

Signed JAR Files

A JarInputStream verifies the signatures of entries in a Signed JAR file when:
  • The Manifest is the first entry in the stream (or the second entry if the first entry in the stream is META-INF/ and the second entry is META-INF/MANIFEST.MF).
  • All signature-related entries immediately follow the Manifest

Once the JarEntry has been completely verified, which is done by reading until the end of the entry's input stream, JarEntry.getCertificates() may be called to obtain the certificates for this entry and JarEntry.getCodeSigners() may be called to obtain the signers.

It is important to note that the verification process does not include validating the signer's certificate. A caller should inspect the return value of JarEntry.getCodeSigners() to further determine if the signature can be trusted.

API Note:
If a JarEntry is modified after the JAR file is signed, a SecurityException will be thrown when the entry is read.
Since:
1.2
See Also:

Field Summary

Modifier and Type Field Description
static final int CENATT
Central directory (CEN) header internal file attributes field offset.
static final int CENATX
Central directory (CEN) header external file attributes field offset.
static final int CENCOM
Central directory (CEN) header comment length field offset.
static final int CENCRC
Central directory (CEN) header uncompressed file crc-32 value field offset.
static final int CENDSK
Central directory (CEN) header disk number start field offset.
static final int CENEXT
Central directory (CEN) header extra field length field offset.
static final int CENFLG
Central directory (CEN) header encrypt, decrypt flags field offset.
static final int CENHDR
Central directory (CEN) header size in bytes (including signature).
static final int CENHOW
Central directory (CEN) header compression method field offset.
static final int CENLEN
Central directory (CEN) header uncompressed size field offset.
static final int CENNAM
Central directory (CEN) header filename length field offset.
static final int CENOFF
Central directory (CEN) header LOC header offset field offset.
static final long CENSIG
Central directory (CEN) header signature.
static final int CENSIZ
Central directory (CEN) header compressed size field offset.
static final int CENTIM
Central directory (CEN) header modification time field offset.
static final int CENVEM
Central directory (CEN) header version made by field offset.
static final int CENVER
Central directory (CEN) header version needed to extract field offset.
static final int ENDCOM
End of central directory (END) header zip file comment length field offset.
static final int ENDHDR
End of central directory (END) header size in bytes (including signature).
static final int ENDOFF
End of central directory (END) header offset for the first CEN header field offset.
static final long ENDSIG
End of central directory (END) header signature.
static final int ENDSIZ
End of central directory (END) header central directory size in bytes field offset.
static final int ENDSUB
End of central directory (END) header number of entries on this disk field offset.
static final int ENDTOT
End of central directory (END) header total number of entries field offset.
static final int EXTCRC
Extra local (EXT) header uncompressed file crc-32 value field offset.
static final int EXTHDR
Extra local (EXT) header size in bytes (including signature).
static final int EXTLEN
Extra local (EXT) header uncompressed size field offset.
static final long EXTSIG
Extra local (EXT) header signature.
static final int EXTSIZ
Extra local (EXT) header compressed size field offset.
static final int LOCCRC
Local file (LOC) header uncompressed file crc-32 value field offset.
static final int LOCEXT
Local file (LOC) header extra field length field offset.
static final int LOCFLG
Local file (LOC) header general purpose bit flag field offset.
static final int LOCHDR
Local file (LOC) header size in bytes (including signature).
static final int LOCHOW
Local file (LOC) header compression method field offset.
static final int LOCLEN
Local file (LOC) header uncompressed size field offset.
static final int LOCNAM
Local file (LOC) header filename length field offset.
static final long LOCSIG
Local file (LOC) header signature.
static final int LOCSIZ
Local file (LOC) header compressed size field offset.
static final int LOCTIM
Local file (LOC) header modification time field offset.
static final int LOCVER
Local file (LOC) header version needed to extract field offset.

Fields declared in class java.util.zip.InflaterInputStream

buf, inf, len

Fields declared in class java.io.FilterInputStream

in

Constructor Summary

Constructor Description
JarInputStream(InputStream in)
Creates a new JarInputStream and reads the optional manifest.
JarInputStream(InputStream in, boolean verify)
Creates a new JarInputStream and reads the optional manifest.

Method Summary

Modifier and Type Method Description
protected ZipEntry createZipEntry(String name)
Creates a new JarEntry (ZipEntry) for the specified JAR file entry name.
Manifest getManifest()
Returns the Manifest for this JAR file when it is the first entry in the stream (or the second entry if the first entry in the stream is META-INF/ and the second entry is META-INF/MANIFEST.MF), or null otherwise.
ZipEntry getNextEntry()
Reads the next ZIP file entry and positions the stream at the beginning of the entry data.
JarEntry getNextJarEntry()
Reads the next JAR file entry and positions the stream at the beginning of the entry data.
int read(byte[] b, int off, int len)
Reads from the current JAR entry into an array of bytes, returning the number of inflated bytes.

Methods declared in class java.util.zip.ZipInputStream

available, close, closeEntry, read, readAllBytes, readNBytes, readNBytes, skip, skipNBytes, transferTo

Methods declared in class java.util.zip.InflaterInputStream

fill, mark, markSupported, reset

Methods declared in class java.io.FilterInputStream

read

Methods declared in class java.io.InputStream

nullInputStream

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

LOCSIG

static final long LOCSIG
Local file (LOC) header signature.
See Also:

EXTSIG

static final long EXTSIG
Extra local (EXT) header signature.
See Also:

CENSIG

static final long CENSIG
Central directory (CEN) header signature.
See Also:

ENDSIG

static final long ENDSIG
End of central directory (END) header signature.
See Also:

LOCHDR

static final int LOCHDR
Local file (LOC) header size in bytes (including signature).
See Also:

EXTHDR

static final int EXTHDR
Extra local (EXT) header size in bytes (including signature).
See Also:

CENHDR

static final int CENHDR
Central directory (CEN) header size in bytes (including signature).
See Also:

ENDHDR

static final int ENDHDR
End of central directory (END) header size in bytes (including signature).
See Also:

LOCVER

static final int LOCVER
Local file (LOC) header version needed to extract field offset.
See Also:

LOCFLG

static final int LOCFLG
Local file (LOC) header general purpose bit flag field offset.
See Also:

LOCHOW

static final int LOCHOW
Local file (LOC) header compression method field offset.
See Also:

LOCTIM

static final int LOCTIM
Local file (LOC) header modification time field offset.
See Also:

LOCCRC

static final int LOCCRC
Local file (LOC) header uncompressed file crc-32 value field offset.
See Also:

LOCSIZ

static final int LOCSIZ
Local file (LOC) header compressed size field offset.
See Also:

LOCLEN

static final int LOCLEN
Local file (LOC) header uncompressed size field offset.
See Also:

LOCNAM

static final int LOCNAM
Local file (LOC) header filename length field offset.
See Also:

LOCEXT

static final int LOCEXT
Local file (LOC) header extra field length field offset.
See Also:

EXTCRC

static final int EXTCRC
Extra local (EXT) header uncompressed file crc-32 value field offset.
See Also:

EXTSIZ

static final int EXTSIZ
Extra local (EXT) header compressed size field offset.
See Also:

EXTLEN

static final int EXTLEN
Extra local (EXT) header uncompressed size field offset.
See Also:

CENVEM

static final int CENVEM
Central directory (CEN) header version made by field offset.
See Also:

CENVER

static final int CENVER
Central directory (CEN) header version needed to extract field offset.
See Also:

CENFLG

static final int CENFLG
Central directory (CEN) header encrypt, decrypt flags field offset.
See Also:

CENHOW

static final int CENHOW
Central directory (CEN) header compression method field offset.
See Also:

CENTIM

static final int CENTIM
Central directory (CEN) header modification time field offset.
See Also:

CENCRC

static final int CENCRC
Central directory (CEN) header uncompressed file crc-32 value field offset.
See Also:

CENSIZ

static final int CENSIZ
Central directory (CEN) header compressed size field offset.
See Also:

CENLEN

static final int CENLEN
Central directory (CEN) header uncompressed size field offset.
See Also:

CENNAM

static final int CENNAM
Central directory (CEN) header filename length field offset.
See Also:

CENEXT

static final int CENEXT
Central directory (CEN) header extra field length field offset.
See Also:

CENCOM

static final int CENCOM
Central directory (CEN) header comment length field offset.
See Also:

CENDSK

static final int CENDSK
Central directory (CEN) header disk number start field offset.
See Also:

CENATT

static final int CENATT
Central directory (CEN) header internal file attributes field offset.
See Also:

CENATX

static final int CENATX
Central directory (CEN) header external file attributes field offset.
See Also:

CENOFF

static final int CENOFF
Central directory (CEN) header LOC header offset field offset.
See Also:

ENDSUB

static final int ENDSUB
End of central directory (END) header number of entries on this disk field offset.
See Also:

ENDTOT

static final int ENDTOT
End of central directory (END) header total number of entries field offset.
See Also:

ENDSIZ

static final int ENDSIZ
End of central directory (END) header central directory size in bytes field offset.
See Also:

ENDOFF

static final int ENDOFF
End of central directory (END) header offset for the first CEN header field offset.
See Also:

ENDCOM

static final int ENDCOM
End of central directory (END) header zip file comment length field offset.
See Also:

Constructor Details

JarInputStream

public JarInputStream(InputStream in) throws IOException
Creates a new JarInputStream and reads the optional manifest. If a manifest is present, also attempts to verify the signatures if the JarInputStream is signed.
Parameters:
in - the actual input stream
Throws:
IOException - if an I/O error has occurred

JarInputStream

public JarInputStream(InputStream in, boolean verify) throws IOException
Creates a new JarInputStream and reads the optional manifest. If a manifest is present and verify is true, also attempts to verify the signatures if the JarInputStream is signed.
Parameters:
in - the actual input stream
verify - whether or not to verify the JarInputStream if it is signed.
Throws:
IOException - if an I/O error has occurred

Method Details

getManifest

public Manifest getManifest()
Returns the Manifest for this JAR file when it is the first entry in the stream (or the second entry if the first entry in the stream is META-INF/ and the second entry is META-INF/MANIFEST.MF), or null otherwise.
Returns:
the Manifest for this JAR file, or null otherwise.

getNextEntry

public ZipEntry getNextEntry() throws IOException
Reads the next ZIP file entry and positions the stream at the beginning of the entry data. If verification has been enabled, any invalid signature detected while positioning the stream for the next entry will result in an exception.
Overrides:
getNextEntry in class ZipInputStream
Returns:
the next ZIP file entry, or null if there are no more entries
Throws:
ZipException - if a ZIP file error has occurred
IOException - if an I/O error has occurred
SecurityException - if any of the jar file entries are incorrectly signed.

getNextJarEntry

public JarEntry getNextJarEntry() throws IOException
Reads the next JAR file entry and positions the stream at the beginning of the entry data. If verification has been enabled, any invalid signature detected while positioning the stream for the next entry will result in an exception.
Returns:
the next JAR file entry, or null if there are no more entries
Throws:
ZipException - if a ZIP file error has occurred
IOException - if an I/O error has occurred
SecurityException - if any of the jar file entries are incorrectly signed.

read

public int read(byte[] b, int off, int len) throws IOException
Reads from the current JAR entry into an array of bytes, returning the number of inflated bytes. If len is not zero, the method blocks until some input is available; otherwise, no bytes are read and 0 is returned.

If the current entry is compressed and this method returns a nonzero integer n then buf[off] through buf[off+n-1] contain the uncompressed data. The content of elements buf[off+n] through buf[off+len-1] is undefined, contrary to the specification of the InputStream superclass, so an implementation is free to modify these elements during the inflate operation. If this method returns -1 or throws an exception then the content of buf[off] through buf[off+len -1] is undefined.

If verification has been enabled, any invalid signature on the current entry will be reported at some point before the end of the entry is reached.

Overrides:
read in class ZipInputStream
Parameters:
b - the buffer into which the data is read
off - the start offset in the destination array b
len - the maximum number of bytes to read
Returns:
the actual number of bytes read, or -1 if the end of the entry is reached
Throws:
NullPointerException - If b is null.
IndexOutOfBoundsException - If off is negative, len is negative, or len is greater than b.length - off
ZipException - if a ZIP file error has occurred
IOException - if an I/O error has occurred
SecurityException - if any of the jar file entries are incorrectly signed.
See Also:

createZipEntry

protected ZipEntry createZipEntry(String name)
Creates a new JarEntry (ZipEntry) for the specified JAR file entry name. The manifest attributes of the specified JAR file entry name will be copied to the new JarEntry.
Overrides:
createZipEntry in class ZipInputStream
Parameters:
name - the name of the JAR/ZIP file entry
Returns:
the JarEntry object just created

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/jar/JarInputStream.html