java-如何使用gzip将图像转换为base64字符串

我正在尝试转换和压缩从android上的文件路径获取的图像,以使用base64的gzip进行转换(我正在使用它,因为我的桌面版本是用Java编写的,因此也是如此).这是我目前用于压缩的内容：

Bitmap bm = BitmapFactory.decodeFile(imagePath);              
ByteArrayOutputStream baos = new ByteArrayOutputStream();     
bm.compress(Bitmap.CompressFormat.JPEG, 100, baos);           
byte[] data = baos.toByteArray();                                                               
String base64Str = null;                                      

ByteArrayOutputStream out_bytes = new ByteArrayOutputStream();
OutputStream out = new Base64.OutputStream(out_bytes);

try {
    out.write(data);
    out.close();                                                         
    byte[] encoded = out_bytes.toByteArray();                 

    base64Str = Base64.encodeBytes(encoded, Base64.GZIP);     
    baos.close();                                             
} catch (Exception e) {}

解决方法:

这是您的代码当前正在执行的操作：

//1. Decode data from image file
Bitmap bm = BitmapFactory.decodeFile(imagePath);
...
//2. Compress decoded image data to JPEG format with max quality
bm.compress(Bitmap.CompressFormat.JPEG, 100, baos);
...
//3. Encode compressed image data to base64
out.write(data);
...
//4. Compress to gzip format, before encoding gzipped data to base64
base64Str = Base64.encodeBytes(encoded, Base64.GZIP);

我不知道您的台式机版本是如何做到的,但是步骤3是不必要的,因为您要执行与步骤4相同的操作.

(已删除部分答案)

编辑：以下代码将从文件中读取字节,对这些字节进行gzip压缩并将其编码为base64.它适用于所有小于2 GB的可读文件.传递给Base64.encodeBytes的字节将与文件中的字节相同,因此不会丢失任何信息(与上面的代码相反,在上面的代码中,您首先将数据转换为JPEG格式).

/*
 * imagePath has changed name to path, as the file doesn't have to be an image.
 */
File file = new File(path);
long length = file.length();
BufferedInputStream bis = null;
try {
    bis = new BufferedInputStream(new FileInputStream(file));
    if(length > Integer.MAX_VALUE) {
        throw new IOException("File must be smaller than 2 GB.");
    }
    byte[] data = new byte[(int)length];
    //Read bytes from file
    bis.read(data);
} catch (IOException e) {
    e.printstacktrace();
} finally {
    if(bis != null)
        try { bis.close(); }
        catch(IOException e) {}
}
//Gzip and encode to base64
String base64Str = Base64.encodeBytes(data, Base64.GZIP);

EDIT2：这应该解码base64字符串,并将解码的数据写入文件：

    //outputPath is the path to the destination file.

    //Decode base64 String (automatically detects and decompresses gzip)
    byte[] data = Base64.decode(base64str);
    FileOutputStream fos = null;
    try {
        fos = new FileOutputStream(outputPath);
        //Write data to file
        fos.write(data);
    } catch(IOException e) {
        e.printstacktrace();
    } finally {
        if(fos != null)
            try { fos.close(); }
            catch(IOException e) {}
    }