Extract contents of Zip file downloaded using a HTTP GET request

Question

I have to download a Zip file, from rest call and extract its contents (some PDF files and a PNG file).

I'm using Java Spring.

How can do it?

Answer 1

You can use Spring's RestTemplate to download the file

RestTemplate templ = new RestTemplate();
byte[] downloadedBytes = templ.getForObject(url, byte[].class);

Extract the contents with standard java or a third party library.

Example utility, adapted from here: http://www.codejava.net/java-se/file-io/programmatically-extract-a-zip-file-using-java

package com.test;

import java.io.BufferedOutputStream;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;

public class ZipHelper {

    private static final int BUFFER_SIZE = 4096;

    public static void unzip(byte[] data, String dirName) throws IOException {
        File destDir = new File(dirName);
        if (!destDir.exists()) {
            destDir.mkdir();
        }
        ZipInputStream zipIn = new ZipInputStream(new ByteArrayInputStream(data));
        ZipEntry entry = zipIn.getNextEntry();

        while (entry != null) {
            String filePath = dirName + File.separator + entry.getName();
            if (!entry.isDirectory()) {
                // if the entry is a file, extracts it
                extractFile(zipIn, filePath);
            } else {
                // if the entry is a directory, make the directory
                File dir = new File(filePath);
                dir.mkdir();
            }
            zipIn.closeEntry();
            entry = zipIn.getNextEntry();
        }
        zipIn.close();
    }

    private static void extractFile(ZipInputStream zipIn, String filePath) throws IOException {
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(filePath));
        byte[] bytesIn = new byte[BUFFER_SIZE];
        int read = 0;
        while ((read = zipIn.read(bytesIn)) != -1) {
            bos.write(bytesIn, 0, read);
        }
        bos.close();
    }
}

Then you use this utility like so:

ZipHelper.unzip(downloadedBytes, "/path/to/directory");