Byte []和java.lang.OutOfMemoryError按位读取文件 [英] Byte[] and java.lang.OutOfMemoryError reading file by bits

问题描述

我试图写一个阅读器读取文件的位，但我有一个大文件的问题。我尝试读取100 MB的文件，它花了3分钟，但它的工作。

然而，然后我试图与500 MB的文件，但它甚至没有开始。因为这一行：

  byte [] fileBits = new byte [len]; 
  

现在我正在搜索sulutions，找不到任何东西。
也许有人已经解决了它，可以分享一些代码，提示或想法。
$ b $ $ $ $ $ $ $ $ $ $ $ $ if（file.length（） > Integer.MAX_VALUE）{
throw new IllegalArgumentException（File is too large：+ file.length（））;
}

int len =（int）file.length（）;
FileInputStream inputStream = new FileInputStream（file）;

尝试{
byte [] fileBits = new byte [len];
for（int pos = 0; pos< len;）{
int n = inputStream.read（fileBits，pos，len - pos）;
if（n <0）{
throw new EOFException（）;
}
pos + = n;
}

inputStream.read（fileBits，0，inputStream.available（））;
inputStream.close（）;

解决方案

  FileChannel fc = new FileInputStream（file）.getChannel（）; 
 MappedByteBuffer mbb = fc.map（FileChannel.MapMode.READ_ONLY，0，（int）fc.size（））; 
  

这将使整个文件几乎立即可用（大约10毫秒），并且使用旁边没有堆。 BTW该文件必须小于2 GB。

I am trying to write a reader which reads files by bits but I have a problem with large files. I tried to read file with 100 mb and it took over 3 minutes but it worked.

However, then I tried file with 500 mb but it didn't even started. Because of this line:

byte[] fileBits = new byte[len];

Now I am searching for sulutions and can't find any. Maybe someone had solved it and could share some code, tips or idea.

if (file.length() > Integer.MAX_VALUE) {
    throw new IllegalArgumentException("File is too large: " + file.length());
}

int len = (int) file.length();
FileInputStream inputStream = new FileInputStream(file);

try {
    byte[] fileBits = new byte[len];
    for (int pos = 0; pos < len;) {
        int n = inputStream.read(fileBits, pos, len - pos);
        if (n < 0) {
            throw new EOFException();
        }
        pos += n;
    }

inputStream.read(fileBits, 0, inputStream.available());
inputStream.close();

解决方案

I suggest you try memory mapping.

FileChannel fc = new FileInputStream(file).getChannel();
MappedByteBuffer mbb = fc.map(FileChannel.MapMode.READ_ONLY, 0, (int) fc.size());

This will make the whole file available almost immediately (about 10 ms) and uses next to no heap. BTW The file has to be less than 2 GB.

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