在Java中将InputStream转换为字节数组

Question

如何将整个读InputStream入字节数组？

Answer 1

您可以使用Apache Commons IO来处理此类和类似的任务.

该IOUtils类型有一个静态方法来读取InputStream和返回a byte[].

InputStream is;
byte[] bytes = IOUtils.toByteArray(is);

在内部,这会创建一个ByteArrayOutputStream并将字节复制到输出,然后调用toByteArray().它通过复制4KiB块中的字节来处理大文件.

Answer 2

您需要从您的每个字节读取InputStream并将其写入a ByteArrayOutputStream.然后,您可以通过调用检索基础字节数组toByteArray(); 例如

InputStream is = ...
ByteArrayOutputStream buffer = new ByteArrayOutputStream();

int nRead;
byte[] data = new byte[16384];

while ((nRead = is.read(data, 0, data.length)) != -1) {
  buffer.write(data, 0, nRead);
}

return buffer.toByteArray();

Answer 3

最后,二十年后,有了一个简单的解决方案,而不需要第三方库,这要归功于Java 9:

InputStream is;
…
byte[] array = is.readAllBytes();

还要注意便利方法readNBytes(byte[] b, int off, int len)和transferTo(OutputStream)解决重复需求.

Answer 4

使用vanilla Java DataInputStream及其readFully方法(至少从Java 1.4开始存在):

...
byte[] bytes = new byte[(int) file.length()];
DataInputStream dis = new DataInputStream(new FileInputStream(file));
dis.readFully(bytes);
...

这种方法还有其他一些风格,但我一直都在使用这个用例.

Answer 5

如果您碰巧使用谷歌番石榴,它将如此简单:

byte[] bytes = ByteStreams.toByteArray(inputStream);

Answer 6

和往常一样,Spring框架(自3.2.2以来的spring-core)也有适合你的东西:StreamUtils.copyToByteArray()

Answer 7

public static byte[] getBytesFromInputStream(InputStream is) throws IOException {
    ByteArrayOutputStream os = new ByteArrayOutputStream(); 
    byte[] buffer = new byte[0xFFFF];
    for (int len = is.read(buffer); len != -1; len = is.read(buffer)) { 
        os.write(buffer, 0, len);
    }
    return os.toByteArray();
}

Answer 8

你真的需要这个形象byte[]吗？您对byte[]图像文件的完整内容有何期待- 以图像文件所处的格式编码,或RGB像素值？

这里的其他答案向您展示如何将文件读入byte[].您byte[]将包含文件的确切内容,并且您需要解码它以对图像数据执行任何操作.

Java用于读取(和写入)图像的标准API是ImageIO API,您可以在包中找到它javax.imageio.您只需一行代码即可从文件中读取图像:

BufferedImage image = ImageIO.read(new File("image.jpg"));

这会给你一个BufferedImage,而不是一个byte[].要获取的图像数据,可以调用getRaster()的BufferedImage.这将为您提供一个Raster对象,该对象具有访问像素数据的方法(它有几个getPixel()/ getPixels()方法).

查找API文档javax.imageio.ImageIO,java.awt.image.BufferedImage,java.awt.image.Raster等.

默认情况下,ImageIO支持多种图像格式:JPEG,PNG,BMP,WBMP和GIF.可以添加对更多格式的支持(您需要一个实现ImageIO服务提供程序接口的插件).

另请参阅以下教程:使用图像

Answer 9

安全的解决方案（具有close正确的流功能）：

• Java 9+版本：

  final byte[] bytes;
  try (inputStream) {
      bytes = inputStream.readAllBytes();
  }
  

• Java 8版本：

  public static byte[] readAllBytes(InputStream inputStream) throws IOException {
      final int bufLen = 4 * 0x400; // 4KB
      byte[] buf = new byte[bufLen];
      int readLen;
      IOException exception = null;
  
      try {
          try (ByteArrayOutputStream outputStream = new ByteArrayOutputStream()) {
              while ((readLen = inputStream.read(buf, 0, bufLen)) != -1)
                  outputStream.write(buf, 0, readLen);
  
              return outputStream.toByteArray();
          }
      } catch (IOException e) {
          exception = e;
          throw e;
      } finally {
          if (exception == null) inputStream.close();
          else try {
              inputStream.close();
          } catch (IOException e) {
              exception.addSuppressed(e);
          }
      }
  }
  

• Kotlin版本（无法访问Java 9+时）：

  @Throws(IOException::class)
  fun InputStream.readAllBytes(): ByteArray {
      val bufLen = 4 * 0x400 // 4KB
      val buf = ByteArray(bufLen)
      var readLen: Int = 0
  
      ByteArrayOutputStream().use { o ->
          this.use { i ->
              while (i.read(buf, 0, bufLen).also { readLen = it } != -1)
                  o.write(buf, 0, readLen)
          }
  
          return o.toByteArray()
      }
  }
  

  为避免嵌套，use请参见此处。

Answer 10

如果您不想使用Apache commons-io库,则此片段取自sun.misc.IOUtils类.它几乎是使用ByteBuffers的常见实现的两倍:

public static byte[] readFully(InputStream is, int length, boolean readAll)
        throws IOException {
    byte[] output = {};
    if (length == -1) length = Integer.MAX_VALUE;
    int pos = 0;
    while (pos < length) {
        int bytesToRead;
        if (pos >= output.length) { // Only expand when there's no room
            bytesToRead = Math.min(length - pos, output.length + 1024);
            if (output.length < pos + bytesToRead) {
                output = Arrays.copyOf(output, pos + bytesToRead);
            }
        } else {
            bytesToRead = output.length - pos;
        }
        int cc = is.read(output, pos, bytesToRead);
        if (cc < 0) {
            if (readAll && length != Integer.MAX_VALUE) {
                throw new EOFException("Detect premature EOF");
            } else {
                if (output.length != pos) {
                    output = Arrays.copyOf(output, pos);
                }
                break;
            }
        }
        pos += cc;
    }
    return output;
}

Answer 11

在某些情况下有人仍在寻找没有依赖关系的解决方案,如果你有一个文件.

1)DataInputStream

 byte[] data = new byte[(int) file.length()];
 DataInputStream dis = new DataInputStream(new FileInputStream(file));
 dis.readFully(data);
 dis.close();

2)ByteArrayOutputStream

 InputStream is = new FileInputStream(file);
 ByteArrayOutputStream buffer = new ByteArrayOutputStream();
 int nRead;
 byte[] data = new byte[(int) file.length()];
 while ((nRead = is.read(data, 0, data.length)) != -1) {
     buffer.write(data, 0, nRead);
 }

3)RandomAccessFile

 RandomAccessFile raf = new RandomAccessFile(file, "r");
 byte[] data = new byte[(int) raf.length()];
 raf.readFully(data);

Answer 12

ByteArrayOutputStream out = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
while (true) {
    int r = in.read(buffer);
    if (r == -1) break;
    out.write(buffer, 0, r);
}

byte[] ret = out.toByteArray();

Answer 13

Input Stream is ...
ByteArrayOutputStream bos = new ByteArrayOutputStream();
int next = in.read();
while (next > -1) {
    bos.write(next);
    next = in.read();
}
bos.flush();
byte[] result = bos.toByteArray();
bos.close();

Answer 14

@Adamski:你可以完全避免缓冲.

代码复制http://www.exampledepot.com/egs/java.io/File2ByteArray.html(是的,这是很详细,但需要的内存与其他解决方案的一半.)

// Returns the contents of the file in a byte array.
public static byte[] getBytesFromFile(File file) throws IOException {
    InputStream is = new FileInputStream(file);

    // Get the size of the file
    long length = file.length();

    // You cannot create an array using a long type.
    // It needs to be an int type.
    // Before converting to an int type, check
    // to ensure that file is not larger than Integer.MAX_VALUE.
    if (length > Integer.MAX_VALUE) {
        // File is too large
    }

    // Create the byte array to hold the data
    byte[] bytes = new byte[(int)length];

    // Read in the bytes
    int offset = 0;
    int numRead = 0;
    while (offset < bytes.length
           && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
        offset += numRead;
    }

    // Ensure all the bytes have been read in
    if (offset < bytes.length) {
        throw new IOException("Could not completely read file "+file.getName());
    }

    // Close the input stream and return bytes
    is.close();
    return bytes;
}

Answer 15

Java 9 最终会给你一个很好的方法：

InputStream in = ...;
ByteArrayOutputStream bos = new ByteArrayOutputStream();
in.transferTo( bos );
byte[] bytes = bos.toByteArray();