实际上,实践中的差异不到10%,而不是其他人所报道的30%。
使用分析器读写一个5MB文件24次,我的数据平均如下:
char[] = 4139 ms
CharBuffer = 4466 ms
ByteBuffer = 938 (direct) ms
个人测试多次支持CharBuffer。
我还尝试将基于文件的IO替换为内存中的IO,性能类似。如果您正在尝试从一个本地流传输到另一个本地流,则最好使用“直接”ByteBuffer。
在实践中,不到10%的性能差异,我更喜欢CharBuffer。它的语法更清晰,没有多余的变量,并且可以进行更直接的操作(即任何要求CharSequence的内容)。
以下是基准测试...它略有错误,因为BufferedReader是在测试方法内分配的,而不是外部...但是,下面的示例允许您隔离IO时间并消除像字符串或字节流调整其内部内存缓冲区等因素。
public static void main(String[] args) throws Exception {
File f = getBytes(5000000);
System.out.println(f.getAbsolutePath());
try {
System.gc();
List<Main> impls = new java.util.ArrayList<Main>();
impls.add(new CharArrayImpl());
impls.add(new CharBufferImpl());
impls.add(new ByteBufferDirectImpl());
for (int i = 0; i < 25; i++) {
for (Main impl : impls) {
test(f, impl);
}
System.out.println("-----");
if(i==0)
continue;
}
System.gc();
System.out.println("Finished");
return;
} finally {
f.delete();
}
}
static int BUFFER_SIZE = 1000;
static File getBytes(int size) throws IOException {
File f = File.createTempFile("input", ".txt");
FileWriter writer = new FileWriter(f);
Random r = new Random();
for (int i = 0; i < size; i++) {
writer.write(Integer.toString(5));
}
writer.close();
return f;
}
static void test(File f, Main impl) throws IOException {
InputStream in = new FileInputStream(f);
File fout = File.createTempFile("output", ".txt");
try {
OutputStream out = new FileOutputStream(fout, false);
try {
long start = System.currentTimeMillis();
impl.runTest(in, out);
long end = System.currentTimeMillis();
System.out.println(impl.getClass().getName() + " = " + (end - start) + "ms");
} finally {
out.close();
}
} finally {
fout.delete();
in.close();
}
}
public abstract void runTest(InputStream ins, OutputStream outs) throws IOException;
public static class CharArrayImpl extends Main {
char[] buff = new char[BUFFER_SIZE];
public void runTest(InputStream ins, OutputStream outs) throws IOException {
Reader in = new BufferedReader(new InputStreamReader(ins));
Writer out = new BufferedWriter(new OutputStreamWriter(outs));
int n;
while ((n = in.read(buff)) >= 0) {
out.write(buff, 0, n);
}
}
}
public static class CharBufferImpl extends Main {
CharBuffer buff = CharBuffer.allocate(BUFFER_SIZE);
public void runTest(InputStream ins, OutputStream outs) throws IOException {
Reader in = new BufferedReader(new InputStreamReader(ins));
Writer out = new BufferedWriter(new OutputStreamWriter(outs));
int n;
while ((n = in.read(buff)) >= 0) {
buff.flip();
out.append(buff);
buff.clear();
}
}
}
public static class ByteBufferDirectImpl extends Main {
ByteBuffer buff = ByteBuffer.allocateDirect(BUFFER_SIZE * 2);
public void runTest(InputStream ins, OutputStream outs) throws IOException {
ReadableByteChannel in = Channels.newChannel(ins);
WritableByteChannel out = Channels.newChannel(outs);
int n;
while ((n = in.read(buff)) >= 0) {
buff.flip();
out.write(buff);
buff.clear();
}
}
}