Question

如何在java中检查文件是否为gzip。我通过读取前2个字节并与魔术代码进行比较来检查。但是对于大尺寸的文件获取OutOfMemoryError。任何人都知道其他方法吗？

Answer 1

使用我在google上找到的这个包：

package example;
 
import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.util.zip.GZIPInputStream;
 
public class GZipUtil {
 
 /**
  * Checks if an input stream is gzipped.
  * 
  * @param in
  * @return
  */
 public static boolean isGZipped(InputStream in) {
  if (!in.markSupported()) {
   in = new BufferedInputStream(in);
  }
  in.mark(2);
  int magic = 0;
  try {
   magic = in.read() & 0xff | ((in.read() << 8) & 0xff00);
   in.reset();
  } catch (IOException e) {
   e.printStackTrace(System.err);
   return false;
  }
  return magic == GZIPInputStream.GZIP_MAGIC;
 }
 
 /**
  * Checks if a file is gzipped.
  * 
  * @param f
  * @return
  */
 public static boolean isGZipped(File f) {
  int magic = 0;
  try {
   RandomAccessFile raf = new RandomAccessFile(f, "r");
   magic = raf.read() & 0xff | ((raf.read() << 8) & 0xff00);
   raf.close();
  } catch (Throwable e) {
   e.printStackTrace(System.err);
  }
  return magic == GZIPInputStream.GZIP_MAGIC;
 }
 
 public static void main(String[] args) throws FileNotFoundException {
  File gzf = new File("/tmp/1.gz");
 
  // Check if a file is gzipped.
  System.out.println(isGZipped(gzf));
 
  // Check if a input stream is gzipped.
  System.out.println(isGZipped(new FileInputStream(gzf)));
 }
}

Answer 2

尝试Files.probeContentType(Path) [JDK 7]

Path source = Paths.get("D:/myfiles/a.zip");
System.out.println(Files.probeContentType(source));

<强>输出

application/x-zip-compressed

Answer 3

使用gzip输入流http://docs.oracle.com/javase/7/docs/api/java/util/zip/GZIPInputStream.html。如果您尝试打开另一种格式，它会抛出ZipException。在您的代码中，您可以在catchblock中捕获此异常。

Answer 4

你应该只读取文件中的2个字节，如果你正在检查它，听起来就像是把整个文件拉进了内存。

https://docs.oracle.com/javase/tutorial/essential/io/datastreams.html

Answer 5

这就是我正在使用的

private static void decompressGzipFile(String gzipFilePath, String newFilePath) {
        try {
            FileInputStream fis = new FileInputStream(gzipFile);
            GZIPInputStream gis = new GZIPInputStream(fis);
            // If this line does not throw exception your file is GZip
            // Your logic


        } catch (IOException e) {
            //Not in GZip Format
        }

    }

如何在java中检查文件是否为gzip

5 个答案: