Android MappedByteBuffer文件映射内存使用示例¶
频繁读写io会造成性能问题。有没有另外一种读写文件的方式呢？
使用RandomAccessFile来获取MappedByteBuffer。
private static void writeDemo() {
System.out.println("[writeDemo] start");
String inputStr = "This write demo. 维多利亚女王纪念碑是位于英国伦敦的一座大型纪念碑和雕塑组合，建于1911年。";
byte[] inputBytes = inputStr.getBytes();
final int length = inputBytes.length;
try {
RandomAccessFile randomAccessFile = new RandomAccessFile("out/writeDemo.txt", "rw");
MappedByteBuffer mappedByteBuffer = randomAccessFile.getChannel().map(FileChannel.MapMode.READ_WRITE, 0, length);
mappedByteBuffer.put(inputBytes);
} catch (Exception e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
System.out.println("[writeDemo] end");
}
private static void writeAppendDemo() {
System.out.println("[writeAppendDemo] start");
String appendText = "\nThis is append text. 纪念碑的基座由2300吨汉白玉构成。";
byte[] bytes = appendText.getBytes();
final int length = bytes.length;
try {
RandomAccessFile randomAccessFile = new RandomAccessFile("out/writeDemo.txt", "rw");
MappedByteBuffer mappedByteBuffer = randomAccessFile.getChannel().map(FileChannel.MapMode.READ_WRITE, randomAccessFile.length(), length);
mappedByteBuffer.put(bytes);
} catch (Exception e) {
System.out.println(e.getMessage());
e.printStackTrace();
}
System.out.println("[writeAppendDemo] end");
}
Android中使用MappedByteBuffer写入文件。记住当前写文件的位置gCurrentLogPos，处理文件增长的问题。
File dir = new File(logFileDir);
if (!dir.exists()) {
boolean mk = dir.mkdirs();
Log.d(defTag, "make dir " + mk);
}
File eFile = new File(logFileDir + File.separator + fileName);
byte[] strBytes = logContent.getBytes();
try {
RandomAccessFile randomAccessFile = new RandomAccessFile(eFile, "rw");
MappedByteBuffer mappedByteBuffer;
final int inputLen = strBytes.length;
if (!eFile.exists()) {
boolean nf = eFile.createNewFile();
Log.d(defTag, "new log file " + nf);
mappedByteBuffer = randomAccessFile.getChannel().map(FileChannel.MapMode.READ_WRITE, gCurrentLogPos, LOG_FILE_GROW_SIZE);
} else {
mappedByteBuffer = randomAccessFile.getChannel().map(FileChannel.MapMode.READ_WRITE, gCurrentLogPos, inputLen);
}
if (mappedByteBuffer.remaining() < inputLen) {
mappedByteBuffer = randomAccessFile.getChannel().map(FileChannel.MapMode.READ_WRITE, gCurrentLogPos, LOG_FILE_GROW_SIZE + inputLen);
}
mappedByteBuffer.put(strBytes);
gCurrentLogPos += inputLen;
} catch (Exception e) {
Log.e(defTag, "WriteRunnable run: ", e);
if (!eFile.exists()) {
boolean nf = eFile.createNewFile();
Log.d(defTag, "new log file " + nf);
}
FileOutputStream os = new FileOutputStream(eFile, true);
os.write(logContent.getBytes());
os.flush();
os.close();
}
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