Java – Decompress a Gzip file
In previous article, we show how to compress a file in Gzip format. This article shows how to decompress a Gzip file.
1. Decompress a Gzip file – GZIPInputStream
1.1 This example decompress a Gzip file sitemap.xml.gz
back to its original file sitemap.xml
. We copy the GZIPInputStream into a FileOutputStream
to decompress a Gzip file.
GZipExample.java
package com.mkyong.io.howto.compress;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.zip.GZIPInputStream;
public class GZipExample {
public static void main(String[] args) {
Path source = Paths.get("/home/mkyong/test/sitemap.xml.gz");
Path target = Paths.get("/home/mkyong/test/sitemap.xml");
if (Files.notExists(source)) {
System.err.printf("The path %s doesn't exist!", source);
return;
}
try {
GZipExample.decompressGzip(source, target);
} catch (IOException e) {
e.printStackTrace();
}
}
public static void decompressGzip(Path source, Path target) throws IOException {
try (GZIPInputStream gis = new GZIPInputStream(
new FileInputStream(source.toFile()));
FileOutputStream fos = new FileOutputStream(target.toFile())) {
// copy GZIPInputStream to FileOutputStream
byte[] buffer = new byte[1024];
int len;
while ((len = gis.read(buffer)) > 0) {
fos.write(buffer, 0, len);
}
}
}
}
2. Decompress a Gzip file, again.
2.1 This example is similar to example 1; instead, we use NIO File.copy
to copy a file.
import java.nio.file.Files;
import java.util.zip.GZIPInputStream;
//...
public static void decompressGzipNio(Path source, Path target) throws IOException {
try (GZIPInputStream gis = new GZIPInputStream(
new FileInputStream(source.toFile()))) {
Files.copy(gis, target);
}
}
3. Decompress a Gzip file to byte arrays
3.1 This example decompress a Gzip file into a byte[]
directly without saving it into a local file.
GZipExample3.java
package com.mkyong.io.howto.compress;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.zip.GZIPInputStream;
public class GZipExample3 {
public static void main(String[] args) {
// decompress
Path source = Paths.get("/home/mkyong/test/sitemap.xml.gz");
if (Files.notExists(source)) {
System.err.printf("The path %s doesn't exist!", source);
return;
}
try {
byte[] bytes = GZipExample.decompressGzipToBytes(source);
// do task for the byte[]
//convert byte[] to string for display
System.out.println(new String(bytes, StandardCharsets.UTF_8));
} catch (IOException e) {
e.printStackTrace();
}
}
// decompress a Gzip file into a byte arrays
public static byte[] decompressGzipToBytes(Path source) throws IOException {
ByteArrayOutputStream output = new ByteArrayOutputStream();
try (GZIPInputStream gis = new GZIPInputStream(
new FileInputStream(source.toFile()))) {
// copy GZIPInputStream to ByteArrayOutputStream
byte[] buffer = new byte[1024];
int len;
while ((len = gis.read(buffer)) > 0) {
output.write(buffer, 0, len);
}
}
return output.toByteArray();
}
}
Download Source Code
$ git clone https://github.com/mkyong/core-java
$ cd java-io
It is a good idea to put the close() method calls within finally clause, prevents resource leakage 😉
Thanks for your feedback, we updated the code again, using
try-with-resources
to auto close the resources.Following your example I wrote below how to do same thing but to
retrieve gziped text files to a String.
Is there any better container then String for big xml files?
Blob blob = rs.getBlob("ACR_FILE_CONTENT");
byte[] bdata = blob.getBytes(1, (int) blob.length());
ByteArrayInputStream bais = new ByteArrayInputStream(bdata);
String text=gunzipIt(bais,"UTF-8");
public static String gunzipIt(ByteArrayInputStream bais, String format){
byte[] buffer = new byte[1024];
String str=null;
if(format==null||format.isEmpty()){
format="UTF-8";
}
try{
GZIPInputStream gzis = new GZIPInputStream(bais);
ByteArrayOutputStream out = new ByteArrayOutputStream();
int len;
while ((len = gzis.read(buffer)) > 0)
{
out.write(buffer, 0, len);
}
str=out.toString(format);
gzis.close();
out.close();
}catch(IOException ex){
ex.printStackTrace();
}
return str;
}
Normally, I will return a
byte[]