Java Foundation----Use of >zip compression

Java provides read and write data streams in a compressed format. They are encapsulated into out-of-the-box IO classes to provide compression capabilities. Let's start with the use of compressed files in Java.

Directory Navigation:

1. A brief description of compression
2. Use of gzip compressed files
3. Use of Zip compressed files
4. Comparison of gzip with zip compression
5. Friendship Link

A brief description of compression

First, there are compressed classes in Java:

• Checkedinputstream getchecksum () generates checksums for any inputstream (not just decompression)
• Checkedoutputstream getchecksum () generates checksums for any outputstream (not just decompression)
• Deflateroutputstream the underlying class for compressing classes
• Zipoutputstream a deflateroutputstream to compress the data into a ZIP file format
• Gzipoutputstream a deflateroutputstream to compress data into gzip file format
• Inflaterinputstream the base class for extracting classes
• Zipinputstream a deflaterinputstream, unzip the data saved in the ZIP file format
• Gzipinputstream a deflaterinputstream, unzip the data saved in the gzip file format

Second, some description of the compression library:

• Compressed class libraries are processed in bytes rather than characters, and they are part of the InputStream and OutputStream inheritance hierarchies

Third, the use of zip compression Note:

• For each file that you want to add to the archive, you must call Putnextentry () and pass it to a ZipEntry object.
• The ZipEntry object contains a fully functional interface that allows you to get and set all the data that is acceptable on that particular entry (portal) in the zip file: First name, length before compression and compression, date, CRC checksum, data for extra fields, comments, The compression method and whether it is a directory entry, and so on.
• Although Checkedinputstream and Checkedoutputstream also provide support for Adler32 and CRC32 checksums, the ZipEntry only supports CRC interfaces
• To extract the files, Zipinputstream provides a getnextentry () method to return to the next zipentry under some conditions
• You can use the ZipFile object to read the file. The object has a entries () method that can return a enumeration (enumeration) for ZipEntry.

Use of gzip compressed files

We use a simple program use case to expand today's usage of the compression class, the program structure is as follows

First, we create a gzipcompress class, used for the Gzip compression class test: firstly, the compressed file Method compress ():

Compressed file private static void compress () throws Exception {    BufferedReader in = new BufferedReader (New FileReader ("Compr Ess/test.txt ")));    Bufferedoutputstream out = new Bufferedoutputstream (new Gzipoutputstream (New FileOutputStream ("uncompress/test.gz")) );    int C;    while ((c = In.read ())! =-1) {        out.write (c);    }    In.close ();    Out.close ();}

Second, we create the Gzip decompression method: Uncompress ()

Unzip the file private static void Uncompress () throws Exception {    BufferedReader in = new BufferedReader (            new Inputstr Eamreader (New Gzipinputstream (New FileInputStream ("uncompress/test.gz")));    String str;    while ((str = in.readline ()) = null) {        System.out.println (str);    }    In.close ();}

Third, in the main method to run, the following results are obtained:

• Console printing: Hello world.
• Generate test.gz files under the Uncompress folder

Use of Zip compressed files

One, we create a zipcompress class for the Gzip compression class test: First, the compressed file Method compress (): Compressed Huhx.png,test2.txt, Test3.txt, test4.txt file

Private final static string[] resources = new string[] {"Huhx.png", "Test2.txt", "Test3.txt", "Test4.txt"};//compressed file privat    e static void Compress () throws Exception {FileOutputStream f = new FileOutputStream ("Uncompress/test.zip");    Checkedoutputstream csum = new Checkedoutputstream (f, New Adler32 ());    Zipoutputstream Zos = new Zipoutputstream (csum);    Bufferedoutputstream out = new Bufferedoutputstream (ZOS);    Zos.setcomment ("A test of Java zipping");    ZipEntry entry = null;        for (String resource:resources) {System.out.println ("Writing file:" + Resource);        BufferedReader in = new BufferedReader (New FileReader ("compress/" + Resource));        Entry = new ZipEntry (Resource);        Entry.setcomment (Resource + "comments");        Zos.putnextentry (entry);        int C;        while ((c = In.read ())! =-1) {out.write (c);        } in.close ();    Out.flush ();    } out.close (); System.out.println ("Checksum:" + csum.getchecksum (). GetValue ());} 

Second, we create the Zip decompression method: Uncompress1 ()

Unzip the file private static void Uncompress1 () throws Exception {    FileInputStream fi = new FileInputStream ("Uncompress/tes T.zip ");    Checkedinputstream csum = new Checkedinputstream (FI, New Adler32 ());    Zipinputstream in2 = new Zipinputstream (csum);    Bufferedinputstream bis = new Bufferedinputstream (in2);    ZipEntry ze;    while ((Ze = in2.getnextentry ()) = null) {        System.out.println ("Reading file:" + ze.getname ());    }    System.out.println ("Checksum:" + csum.getchecksum (). GetValue ());    Bis.close ();}

Third, we create a zip decompression another method: Uncompress2 ()

Unzip the file private static void Uncompress2 () throws Exception {    ZipFile ZF = new ZipFile ("Uncompress/test.zip");    Enumeration<?> e = zf.entries ();    while (E.hasmoreelements ()) {        ZipEntry entry = (zipentry) e.nextelement ();        System.out.println ("File:" + entry.getcomment ());    }    Zf.close ();}

Iv. run the Compress () and Uncompress1 () methods to obtain the following results:

V. Run the Compress () and Uncompress2 () methods to obtain the following results:

Comparison of gzip with zip compression

• GZIP: If only a single data stream needs to be compressed (rather than a series of different data), then it might be the most appropriate choice.
• ZIP: It makes it easy to save multiple files. There is even a separate class to simplify the reading of the zip file

Friendship Link

• Test Project source code download access password 56C3

Http://www.cnblogs.com/huhx/p/javaCompress.html

Java Foundation----Use of >zip compression (RPM)