追加模式创建的FileOutputStream获取的FileChannel设置position不影响写入位置

@Test
	public void append(){
		DateTimeFormatter df = DateTimeFormatter.ofPattern("HH:mm");
		try {
            //追加模式创建FileOutputStream
			FileOutputStream fos = new FileOutputStream("d:/tmp/1.txt",true);
			FileChannel fc = fos.getChannel();
			ByteBuffer buffer = ByteBuffer.wrap(df.format(LocalTime.now()).getBytes("utf-8"));
			println("A fileChannel.position ()= " + fc.position());
			println("channel size="+fc.size());
            //此处无论position设置成什么值，下面的write方法都是在文件末尾追加内容
			fc.position(0);
			println("A fileChannel.position ()= " + fc.position());
			println( "write() 1 返回值 ：" + fc.write(buffer)) ;
			println ("B fileChannel .position ()= " + fc.position());
			fc.close();
			fos.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

    public long position() throws IOException {
        this.ensureOpen();
        synchronized(this.positionLock) {
            long var2 = -1L;
            int var4 = -1;

            long var5;
            try {
                this.begin();
                var4 = this.threads.add();
                if (this.isOpen()) {
                    do {
                        //通过position(long newPos)方法后看下this.nd.seek(this.fd, -1L)返回的值就知道其实设置position是成功的
                        var2 = this.append ? this.nd.size(this.fd) : this.nd.seek(this.fd, -1L);
                    } while(var2 == -3L && this.isOpen());

                    var5 = IOStatus.normalize(var2);
                    return var5;
                }

                var5 = 0L;
            } finally {
                this.threads.remove(var4);
                this.end(var2 > -1L);

                assert IOStatus.check(var2);

            }

            return var5;
        }
    }

    int write(FileDescriptor var1, long var2, int var4) throws IOException {
        return write0(var1, var2, var4, this.append);
    }

JNIEXPORT jint JNICALL
Java_sun_nio_ch_FileDispatcherImpl_write0(JNIEnv *env, jclass clazz, jobject fdo,
                                          jlong address, jint len, jboolean append)
{
    BOOL result = 0;
    DWORD written = 0;
    HANDLE h = (HANDLE)(handleval(env, fdo));

    if (h != INVALID_HANDLE_VALUE) {
        OVERLAPPED ov;
        LPOVERLAPPED lpOv;
        //针对追加模式，特殊处理，所以不管之前position设置的位置如何，如果以追加模式打开文件，
       //在windows系统都会把数据追加到文件末尾，而不是position设置的位置
        if (append == JNI_TRUE) {
            ov.Offset = (DWORD)0xFFFFFFFF;
            ov.OffsetHigh = (DWORD)0xFFFFFFFF;
            ov.hEvent = NULL;
            lpOv = &ov;
        } else {
            lpOv = NULL;
        }
        result = WriteFile(h,           /* File handle to write */
                      (LPCVOID)address, /* pointers to the buffers */
                      len,              /* number of bytes to write */
                      &written,         /* receives number of bytes written */
                      lpOv);            /* overlapped struct */
    }

    if ((h == INVALID_HANDLE_VALUE) || (result == 0)) {
        JNU_ThrowIOExceptionWithLastError(env, "Write failed");
    }

    return convertReturnVal(env, (jint)written, JNI_FALSE);
}