The example shows how to compress and uncompress 7z files using Java

Compress to 7z file
First of all, there is very little compressed content for 7z on the network.
In particular, Java calls compress less.
The following is a compression done by itself.
I conducted the test and it was successful.
To write a compressed stream as to disk in a compressed file.
Then use 7z compression software to open the decompression.

7 - the open source project 7 zip zip - JBinding (link: http://sourceforge.net/projects/sevenzipjbind/)

Without further ado, the method of calling 7z source code to be compressed is as follows.

public byte[] lzmaZip(String xml) throws IOException{ 
  BufferedInputStream inStream = new BufferedInputStream(new ByteArrayInputStream(xml.getBytes())); 
  ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
   
  boolean eos = true; 
    Encoder encoder = new Encoder(); 
    encoder.SetEndMarkerMode(eos); 
    encoder.WriteCoderProperties(bos); 
    long fileSize = xml.length(); 
    if (eos) 
      fileSize = -1; 
    for (int i = 0; i < 8; i++) 
      bos.write((int)(fileSize >>> (8 * i)) & 0xFF); 
    encoder.Code(inStream, bos, -1, -1, null); 
    return bos.toByteArray() ; 
} 

Unzip the 7z file
Use the 7-zip open source project 7-zip-jbinding to unzip a variety of compressed files instead of calling external commands (such as the win call to winrar).

Java's native decompression module has a limited number of decompression types.
Code sample

package core;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Arrays;

import net.sf.sevenzipjbinding.ExtractOperationResult;
import net.sf.sevenzipjbinding.ISequentialOutStream;
import net.sf.sevenzipjbinding.ISevenZipInArchive;
import net.sf.sevenzipjbinding.SevenZip;
import net.sf.sevenzipjbinding.SevenZipException;
import net.sf.sevenzipjbinding.impl.RandomAccessFileInStream;
import net.sf.sevenzipjbinding.simple.ISimpleInArchive;
import net.sf.sevenzipjbinding.simple.ISimpleInArchiveItem;

public class UnZip {


  void extractile(String filepath){
     RandomAccessFile randomAccessFile = null;
      ISevenZipInArchive inArchive = null;

      try {
        randomAccessFile = new RandomAccessFile(filepath, "r");
        inArchive = SevenZip.openInArchive(null, // autodetect archive type
            new RandomAccessFileInStream(randomAccessFile));

        // Getting simple interface of the archive inArchive
        ISimpleInArchive simpleInArchive = inArchive.getSimpleInterface();

        System.out.println("  Hash  |  Size  | Filename");
        System.out.println("----------+------------+---------");

        for (final ISimpleInArchiveItem item : simpleInArchive.getArchiveItems()) {
          final int[] hash = new int[] { 0 };
          if (!item.isFolder()) {
            ExtractOperationResult result;

            final long[] sizeArray = new long[1];
            result = item.extractSlow(new ISequentialOutStream() {
              public int write(byte[] data) throws SevenZipException {

                //Write to file
                FileOutputStream fos;
                try {
                  File file = new File(item.getPath());
                  //error occours below
//                 file.getParentFile().mkdirs();
                  fos = new FileOutputStream(file);
                  fos.write(data);
                  fos.close();

                } catch (FileNotFoundException e) {
                  // TODO Auto-generated catch block
                  e.printStackTrace();
                } catch (IOException e) {
                  // TODO Auto-generated catch block
                  e.printStackTrace();
                }

                hash[0] ^= Arrays.hashCode(data); // Consume data
                sizeArray[0] += data.length;
                return data.length; // Return amount of consumed data
              }
            });
            if (result == ExtractOperationResult.OK) {
              System.out.println(String.format("%9X | %10s | %s", // 
                  hash[0], sizeArray[0], item.getPath()));
            } else {
              System.err.println("Error extracting item: " + result);
            }
          }
        }
      } catch (Exception e) {
        System.err.println("Error occurs: " + e);
        e.printStackTrace();
        System.exit(1);
      } finally {
        if (inArchive != null) {
          try {
            inArchive.close();
          } catch (SevenZipException e) {
            System.err.println("Error closing archive: " + e);
          }
        }
        if (randomAccessFile != null) {
          try {
            randomAccessFile.close();
          } catch (IOException e) {
            System.err.println("Error closing file: " + e);
          }
        }
      }
  }
}

When invoked:

unzip=new UnZip();
unzip.extractile("a.7z");

Will automatically unzip the files in the zip package to the current directory, of course, you can change the Settings to a specific directory. The code is simple and unambiguous. You can go to the discuss search at the sourceforge project address above for questions.