Java IO.pdf - Nguyen Dang Binh

9.1.1.10 Checking the state of a deflater
Java I/O
The Deflater class also provides several methods that return information about the deflater's
state. The getAdler() method returns the Adler-32 checksum of the uncompressed data. This
is not a java.util.zip.Checksum object but the actual int value of the checksum:
public native synchronized int getAdler()
The getTotalIn() method returns the number of uncompressed bytes passed to the
setInput() method:
public native synchronized int getTotalIn()
The getTotalOut() method returns the total number of compressed bytes output so far via
deflate():
public native synchronized int getTotalOut()
For example, to print a running total of the compression achieved by the Deflater object
def, you might do something like this:
System.out.println((1.0 - def.getTotalOut()/def.getTotalIn())*100.0 +
?% saved?);
9.1.2 Inflating Data
The Inflater class contains methods to decompress blocks of data compressed in the zip,
gzip, or zlib formats. This data may have been produced by Java's Deflater class or by some
other program written in another language entirely, such as PKZip or gzip. Using an inflater is
a little simpler than using a deflater, since there aren't a lot of settings to pick. Those were
established when the data was compressed. There are seven steps to inflating data:
1. Construct an Inflater object.
2. Set the input with the compressed data to be inflated.
3. Call needsDictionary() to determine if a preset dictionary is required.
4. If needsDictionary() returns true, call getAdler() to get the Adler-32 checksum
of the dictionary. Then invoke setDictionary() to set the dictionary data.
5. Inflate the data repeatedly until inflate() returns zero.
6. If needsInput() returns true, go back to step 2 to provide additional input data.
7. The finished() method returns true.
If you want to decompress more data with this Inflater object, reset it.
You rarely use this class directly. Instead, you use an inflater indirectly through one of the
decompressing stream classes like InflaterInputStream or InflaterOutputStream. These
classes provide much more convenient programmer interfaces for stream-oriented
decompression.
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