java - 在java中，如何从输入流中读取固定长度并保存为文件？

Question

在java中，如何从输入流中读取固定长度并保存为文件？ 例如。我想从 inputStream 读取 5M，并保存为 downloadFile.txt 或其他内容。(BUFFERSIZE=1024)

FileOutputStream fos = new FileOutputStream(downloadFile);
byte buffer [] = new byte[BUFFERSIZE];
int temp = 0;
while ((temp = inputStream.read(buffer)) != -1)
{
    fos.write(buffer, 0, temp);
}

Answer 1

两个选项:

1. 继续阅读和写作，直到到达输入的末尾或复制了足够的内容:

   byte[] buffer = new byte[1024];
   int bytesLeft = 5 * 1024 * 1024; // Or whatever
   FileInputStream fis = new FileInputStream(input);
   try {
     FileOutputStream fos = new FileOutputStream(output);
     try {
       while (bytesLeft > 0) {
         int read = fis.read(buffer, 0, Math.min(bytesLeft, buffer.length);
         if (read == -1) {
           throw new EOFException("Unexpected end of data");
         }
         fos.write(buffer, 0, read);
         bytesLeft -= read;
       }
     } finally {
       fos.close(); // Or use Guava's Closeables.closeQuietly,
                    // or try-with-resources in Java 7
     }
   } finally {
     fis.close(); 
   }
   

2. 一次调用将所有 5M 数据读入内存，例如使用DataInputStream.readFully，然后一口气写出来。更简单，但显然使用更多内存。