Java-NIO-Channel-笔记

一、通道(Channel):用于源节点与目标节点的连接。

 *   在Java-NIO中负责缓冲区数据的传输。Channel本身不存储数据，需要配合缓冲区进行传输。

 * 二、通道的主要实现类

 *   java.nio.channels.channel 接口:

 *       |---FileChannel

 *       |---SocketChannel

 *       |---ServerSocketChannel

 *       |---DatagramChannel

 * 三、获取通道

 *   1.Java针对支持通道的实现类提供了getChannel()方法

 *     本地IO

 *       FileInputStream/FileOutputStream   

 *       RandomAccessFile

 *     网络IO

 *       Socket

 *       ServerSocket

 *       DatagramSocket

 *   2.在JDK1.7中的NIO.2 针对各个通道提供了静态方法open()

 *   3.在JDK1.7中的NIO.2 的Files工具类  newByteChannel()

 *     

 * 四、通道之间的数据传输

 *   transferFrom()

 *   transferTo()

 *

 * 五、分散(Scatter)与聚集(Gather)

 *    分散读取(Scattering Reads):将通道中的数据分散到多个缓冲区中

 *    聚集写入(Gathering Writes):将多个缓冲区中的数据聚集到通道中

 *

 * 六、字符集  : Charset

 *    编码：字符串 -> 字节数组  (将看的懂的转为看不懂的为编码)
 *    解码：字节数组  -> 字符串 (将看不懂的转为看的懂的为解码)

//利用通道完成文件的复制(非直接缓冲区)
@Test
public void test1() throws IOException{
FileInputStream fileInputStream = new FileInputStream("Java.pdf");
FileOutputStream fileOutputStream = new FileOutputStream("JavaCopy.pdf");

FileChannel inChannel =	fileInputStream.getChannel();
FileChannel outChannel = fileOutputStream.getChannel();

ByteBuffer buf = ByteBuffer.allocate(1024); //分配一个直接缓冲区

while((inChannel.read(buf))!=-1){
buf.flip(); //切换到读取数据模式
outChannel.write(buf);
buf.clear();
}
outChannel.close();
inChannel.close();
fileOutputStream.close();
fileInputStream.close();
}

//使用直接缓冲区完成文件的复制
@Test
public void test2() throws IOException{

//建立通道
FileChannel incChannel = FileChannel.open(Paths.get("Java.pdf"),StandardOpenOption.READ);
FileChannel outChannel = FileChannel.open(Paths.get("JavaCopy.pdf"),StandardOpenOption.WRITE,
StandardOpenOption.READ,StandardOpenOption.CREATE);

//内存映射文件
MappedByteBuffer inMappedByteBuffer = incChannel.map(FileChannel.MapMode.READ_ONLY,0,incChannel.size());
MappedByteBuffer outMappedByteBuffer = outChannel.map(FileChannel.MapMode.READ_WRITE,0,incChannel.size());

//直接对缓冲区进行数据的读写操作
byte[] dst = new byte[inMappedByteBuffer.limit()];
inMappedByteBuffer.get(dst);
outMappedByteBuffer.put(dst);

outChannel.close();
incChannel.close();
}

//通道之间的传输(直接缓冲区)
4000

@Test
public void test3() throws IOException{

//建立通道
FileChannel inChannel =	FileChannel.open(Paths.get("Java.pdf"),StandardOpenOption.READ);
FileChannel outChannel = FileChannel.open(Paths.get("JavaCopy.pdf"),StandardOpenOption.READ,
StandardOpenOption.WRITE,StandardOpenOption.CREATE);

inChannel.transferTo(0,inChannel.size(),outChannel);
//outChannel.transferFrom(inChannel,0,inChannel.size());

outChannel.close();
inChannel.close();
}

//分散与聚集
@Test
public void test4() throws IOException{

RandomAccessFile rsf1 = new RandomAccessFile("Java.pdf","rw");

//1.获取通道
FileChannel channel1 = rsf1.getChannel();

//2.分配指定大小的缓冲区
ByteBuffer buf1 = ByteBuffer.allocate(100);
ByteBuffer buf2 = ByteBuffer.allocate(1024);

//3.分散读取
ByteBuffer[] dsts = {buf1,buf2};
channel1.read(dsts);

for (ByteBuffer byteBuffer : dsts) {
byteBuffer.flip();
}

System.out.println(new String(dsts[0].array(),0,dsts[0].limit()));
System.out.println("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(new String(dsts[1].array(),0,dsts[1].limit()));

RandomAccessFile rsf2 = new RandomAccessFile("JavaCopy.pdf","rw");
FileChannel channel2 = rsf2.getChannel();
channel2.write(dsts);
}

//获取编码集
@Test
public void test5(){
SortedMap<String,Charset> sdm = Charset.availableCharsets();

Set<Entry<String,Charset>> set = sdm.entrySet();

for (Entry<String, Charset> entry : set) {
System.out.println(entry.getKey()+"~~~"+entry.getValue());
}
}

//字符集
@Test
public void test6() throws CharacterCodingException{

Charset cs1 = Charset.forName("GBK");

CharsetEncoder ce = cs1.newEncoder();  //获取编码器

CharsetDecoder cd = cs1.newDecoder(); //获取解码器

CharBuffer cbuf = CharBuffer.allocate(1024);
cbuf.put("测试编码");
cbuf.flip();

ByteBuffer buffer = ce.encode(cbuf);

//解码
CharBuffer cBuf2 = cd.decode(buffer);
System.out.println(cBuf2.toString());
}