java的nio
1.nio的简介
nio的FileChannel类可以获取的方法有 FileInputStream和FileOutputStream以及RandomAccessFile的getChannel方法，或者FileChannel类的open方法等获取，SocketChannel，ServerSocketChannel，DatagramChannel，同样可以Socket，ServerSocket的getChannel方法和open方法（tcp）等获取，DatagramChannel可以通过open方法获取（udf）等方法获取，Pipe也可以同过open等方法获取，他们只是建立通道，并不参与数据的输入和输出，输入和输出是buffer完成的，buffer有直接缓存区和非直接缓存区两种，直接缓存建立在物理内存上的，建立和销毁allocateDirect的空间的开销比较大，传递的效率要比非直接缓冲区要好（因为直接缓存区只需要复制一次，而非直接缓存区需要复制两次，直接缓存区较非直接缓存区减少了一次复制），所以通常用于传递allocateDirect的空间开创的比较大的时候，用利于传输比较大的文件，但是太大例如超过几个G,那么可以通过分段的方式来传输，非直接缓存区是建立在堆上的，受到jvm的限制。
2.同步与异步
同步是发送一个请求后需要等待返回后才可以发送下一条指令，异步没有等待的过程可以发下一条指令，就例如我叫你吃饭，你没来，我就一直等，这就是同步，你没来我就自己吃饭叫做异步
3.阻塞与非阻塞
阻塞相当于一个队里，我与他建立连接以后，那么需要我先完成，后面的都都排队先等着，非阻塞是你们这些需要与我建立连接的部分，我用一个或者多个线程来轮询你们，你们谁先准备就绪就运行谁。
4.Buffer实现的原理
常用的方法有position limit capacity mark reset rewind hasRemaining remaining flip clear isDirect等以及get，put方法（position会相应的移动）但是又较多的重载方法，没有参数的表示返回游标位置的数据或者放入数据，数组表示向数组中放入数据或者向数组中写入数据。
public class ByteBufferTest {
public static void main(String[] args) {
ByteBuffer buffer = ByteBuffer.allocate(10);
if (!buffer.isDirect()) {
System.out.println("非直接缓冲区");// 非直接缓冲区
}
System.out.println(buffer.position());// 位置0
System.out.println(buffer.limit());// 界限10
System.out.println(buffer.capacity());// 开辟的空间10
buffer.put((byte) 'a');
System.out.println("-------------");
System.out.println(buffer.position());// 位置1
System.out.println(buffer.limit());// 界限10
System.out.println(buffer.capacity());// 开辟的空间10
byte[] bys = { (byte) 'b', (byte) 'c' };
buffer.put(bys);
buffer.mark();
System.out.println("-------------");
System.out.println(buffer.position());// 位置3
System.out.println(buffer.limit());// 界限10
System.out.println(buffer.capacity());// 开辟的空间10
buffer.reset();
System.out.println("-------------");
System.out.println(buffer.position());// 位置1
System.out.println(buffer.limit());// 界限10
System.out.println(buffer.capacity());// 开辟的空间10
buffer.flip();// 将limit设置为当前位置，position设置为0
System.out.println("-------------");
System.out.println(buffer.position());// 位置0
System.out.println(buffer.limit());// 界限1
System.out.println(buffer.capacity());// 开辟的空间10
buffer.rewind();// limit不变，position变为0，且去除mark
buffer.flip();
System.out.println("-------------");
System.out.println(buffer.position());// 位置0
System.out.println(buffer.limit());// 界限0
System.out.println(buffer.capacity());// 开辟的空间10
try {
buffer.reset();
System.out.println("-------------");
System.out.println(buffer.position());
System.out.println(buffer.limit());
System.out.println(buffer.capacity());
} catch (Exception e) {
System.out.println("mark标记不存在了");
}
buffer.limit(3);
buffer.position(3);//position<=limit<=capacity
buffer.flip();
System.out.println(buffer.remaining());//position与limit之间还剩多少元素3
System.out.println("-------------");
System.out.println(buffer.position());// 位置0
System.out.println(buffer.limit());// 界限3
System.out.println(buffer.capacity());// 开辟的空间10
while(buffer.hasRemaining()){//position和limit之间是否还有元素
System.out.println((char)buffer.get());// a b c
}
System.out.println("------------");
System.out.println(buffer.position());// 位置3
System.out.println(buffer.limit());// 界限3
System.out.println(buffer.capacity());// 开辟的空间10
byte[] bys1 = { (byte) 'd', (byte) 'e', (byte) 'f'};
buffer.limit(9);
buffer.put(bys1);
buffer.position(7);
/*limit变为等于capacity，position的位置等于limit-position,在limit-position的
数据相应的往前移覆盖position开始的同样多的数据*/
buffer.compact();
System.out.println("------------");
System.out.println(buffer.position());// 位置2
System.out.println(buffer.limit());// 界限10
System.out.println(buffer.capacity());// 开辟的空间10
while(buffer.hasRemaining()){//position和limit之间是否还有元素
System.out.println((char)buffer.get());// c d e f 4个空格
}
}
}
其他的buffer类似
5.FileChannel的获取方式与使用方法
public class FileChannelTest {
public static void main(String[] args) throws IOException {
// 非直接缓冲区
// 方式1
FileChannel channel1 = null;
FileChannel channel2 = null;
try {
channel1 = new FileInputStream("1.txt").getChannel();
channel2 = new FileOutputStream("3.txt").getChannel();
ByteBuffer allocate = ByteBuffer.allocate(1024);
while (channel1.read(allocate) != -1) {
allocate.flip();
channel2.write(allocate);
allocate.clear();
}
} finally {
channel1.close();
channel2.close();
}
// 方式2
FileChannel channel3 = new RandomAccessFile("1.txt", "r").getChannel();
FileChannel channel4 = new RandomAccessFile("4.txt", "rw").getChannel();
ByteBuffer allocate1 = ByteBuffer.allocate(1024);
while (channel3.read(allocate1) != -1) {
allocate1.flip();
channel4.write(allocate1);
allocate1.clear();
}
channel3.close();
channel4.close();
// 方式3
FileChannel open1 = FileChannel.open(Paths.get("1.txt"), StandardOpenOption.READ);
// StandardOpenOption.CREATE
// 有就覆盖，没有就创建，StandardOpenOption.CREATE_NEW有就报错，没有就创建
FileChannel open2 = FileChannel.open(Paths.get("5.txt"), StandardOpenOption.READ, StandardOpenOption.WRITE,
StandardOpenOption.CREATE_NEW);
ByteBuffer allocate2 = ByteBuffer.allocate(1024);
while (open1.read(allocate2) != -1) {
allocate2.flip();
open2.write(allocate2);
allocate2.clear();
}
open1.close();
open2.close();
// 直接缓冲区
// 方式1
FileChannel channel5 = null;
FileChannel channel6 = null;
try {
channel5 = new FileInputStream("1.txt").getChannel();
channel6 = new FileOutputStream("6.txt").getChannel();
MappedByteBuffer map = channel5.map(MapMode.READ_ONLY, 0, channel5.size());
channel6.write(map);
} finally {
channel5.close();
channel6.close();
}
// 方式2
FileChannel open3 = FileChannel.open(Paths.get("1.txt"), StandardOpenOption.READ);
// StandardOpenOption.CREATE有就覆盖，没有就创建，StandardOpenOption.CREATE_NEW有就报错，没有就创建
FileChannel open4 = FileChannel.open(Paths.get("7.txt"), StandardOpenOption.READ, StandardOpenOption.WRITE,
StandardOpenOption.CREATE_NEW);
ByteBuffer allocate3 = ByteBuffer.allocateDirect(1024);
while (open3.read(allocate3) != -1) {
allocate3.flip();
open4.write(allocate3);
allocate3.clear();
}
open3.close();
open4.close();
// 方式3
FileChannel open5 = FileChannel.open(Paths.get("1.txt"), StandardOpenOption.READ);
// StandardOpenOption.CREATE
// 有就覆盖，没有就创建，StandardOpenOption.CREATE_NEW有就报错，没有就创建
FileChannel open6 = FileChannel.open(Paths.get("8.txt"), StandardOpenOption.READ, StandardOpenOption.WRITE,
StandardOpenOption.CREATE_NEW);
MappedByteBuffer map1 = open5.map(MapMode.READ_ONLY, 0, open4.size());
MappedByteBuffer map2 = open6.map(MapMode.READ_WRITE, 0, open4.size());
// open4.size()不能太大否则会超出int的范围
byte[] dst1 = new byte[(int) open4.size()];
// 将数据放入dst1中
map1.get(dst1);
// 将dst1写入文件中
map2.put(dst1);
open5.close();
open6.close();
// 方式4
FileChannel open7 = FileChannel.open(Paths.get("1.txt"), StandardOpenOption.READ);
// StandardOpenOption.CREATE
// 有就覆盖，没有就创建，StandardOpenOption.CREATE_NEW有就报错，没有就创建
FileChannel open8 = FileChannel.open(Paths.get("9.txt"), StandardOpenOption.READ, StandardOpenOption.WRITE,
StandardOpenOption.CREATE_NEW);
open7.transferTo(0, open7.size(), open8);
// open8.transferTo(position, count, target)
open7.close();
open8.close();
}
}
6.直接缓存区域与非直接缓冲区的效率比较
public static void main(String[] args) throws IOException { long start=System.currentTimeMillis(); String filePath="F:/test/1.wmv"; FileChannel inch1 = new FileInputStream(filePath).getChannel(); FileChannel outch1 = new FileOutputStream("2.wmv").getChannel(); ByteBuffer bf1 = ByteBuffer.allocate(2); while(inch1.read(bf1)!=-1){ bf1.flip(); outch1.write(bf1); bf1.clear(); } inch1.close(); outch1.close(); long end=System.currentTimeMillis(); System.out.println(end-start);//189388
//当allocate为4的时候，时间为100988 System.gc(); System.runFinalization(); start=System.currentTimeMillis(); FileChannel inch2 = new FileInputStream(filePath).getChannel(); FileChannel outch2 = new FileOutputStream("3.wmv").getChannel(); ByteBuffer bf2 = ByteBuffer.allocateDirect(2); while(inch2.read(bf2)!=-1){ bf2.flip(); outch2.write(bf2); bf2.clear(); } inch2.close(); outch2.close(); end=System.currentTimeMillis(); System.out.println(end-start);//190209 } }
public static void main(String[] args) throws IOException { long start=System.currentTimeMillis(); String filePath="F:/test/1.wmv"; FileChannel inch1 = new FileInputStream(filePath).getChannel(); FileChannel outch1 = new FileOutputStream("2.wmv").getChannel(); ByteBuffer bf1 = ByteBuffer.allocate(10000); while(inch1.read(bf1)!=-1){ bf1.flip(); outch1.write(bf1); bf1.clear(); } inch1.close(); outch1.close(); long end=System.currentTimeMillis(); System.out.println(end-start);//200 System.gc(); System.runFinalization(); start=System.currentTimeMillis(); FileChannel inch2 = new FileInputStream(filePath).getChannel(); FileChannel outch2 = new FileOutputStream("3.wmv").getChannel(); ByteBuffer bf2 = ByteBuffer.allocateDirect(10000); while(inch2.read(bf2)!=-1){ bf2.flip(); outch2.write(bf2); bf2.clear(); } inch2.close(); outch2.close(); end=System.currentTimeMillis(); System.out.println(end-start);//90 System.gc(); System.runFinalization(); start=System.currentTimeMillis(); FileChannel inch3 = new FileInputStream(filePath).getChannel(); FileChannel outch3 = new FileOutputStream("4.wmv").getChannel(); inch3.transferTo(0, inch3.size(), outch3); inch3.close(); outch3.close(); end=System.currentTimeMillis(); System.out.println(end-start);//33 } }
7.SocketChannel与ServerSocketChannel（TCP）
阻塞式
@Test public void SocketChannelTest() throws IOException{ SocketChannel open1 = SocketChannel.open(); open1.connect(new InetSocketAddress("127.0.0.1", 9898)); FileChannel open2 = FileChannel.open(Paths.get("1.txt"), StandardOpenOption.READ); ByteBuffer allocate = ByteBuffer.allocate(1024); while(open2.read(allocate)!=-1){ allocate.flip(); open1.write(allocate); allocate.clear(); } //关闭输入，解决阻塞问题 open1.shutdownInput(); open1.read(allocate); allocate.flip(); String string = new String(allocate.array()); System.out.println(string); open1.close(); open2.close(); } @Test public void serverSocketChannelTest() throws IOException{ ServerSocketChannel open1 = ServerSocketChannel.open(); open1.bind(new InetSocketAddress(9898)); //阻塞式的方法 SocketChannel accept = open1.accept(); ByteBuffer allocate = ByteBuffer.allocate(1024); FileChannel open2 = FileChannel.open(Paths.get("10.txt"), StandardOpenOption.READ,StandardOpenOption.WRITE,StandardOpenOption.CREATE); while(accept.read(allocate)!=-1){ allocate.flip(); open2.write(allocate); allocate.clear(); } open2.close(); allocate.put("传输完成".getBytes()); accept.write(allocate); open1.close(); }
非阻塞式selector
Channel和Selector配合使用，Channel必须是非阻塞的才能注册到selector上，SocketChannel、ServerSocketChannel、DatagramChannel、Pipe.SinkChannel、Pipe.SourceChannel能使用，FileChannel不适用Selector，因为FileChannel不能切换为非阻塞模式，FileChannel没有继承SelectableChannel；Selector的select方法是一个阻塞式的方法，需要返回值大于0，register()方法的第二个参数，这是一个”interest集合“，Selector对象会包含3种类型的SelectionKey集合，all-keys集合 （当前所有向Selector注册的SelectionKey的集合，Selector的keys()方法返回该集合），selected-keys集合（相关事件已经被Selector捕获的SelectionKey的集合，Selector的selectedKeys()方法返回该集合），cancelled-keys集合 （已经被取消的SelectionKey的集合，Selector没有提供访问这种集合的方法，取消了就不能再利用，所以一般不能用cancel方法），如果关闭了与SelectionKey对象关联的Channel对象，或者调用了SelectionKey对象的cancel方法，这个SelectionKey对象就会被加入到cancelled-keys集合中，当register()方法执行时，新建一个SelectioKey，并把它加入Selector的all-keys集合中SelectionKey就被加入到selected-keys集合中，程序直接调用selected-keys集合的remove()方法，或者调用它的iterator的remove()方法，可以从selected-keys集合中删除一个SelectionKey对象。
@Test public void SocketChannelTest() throws IOException { SocketChannel open1 = SocketChannel.open(); open1.connect(new InetSocketAddress("127.0.0.1", 9898)); // 设置为非阻塞式 open1.configureBlocking(false); ByteBuffer allocate = ByteBuffer.allocate(1024); Scanner scanner = new Scanner(System.in); while (true) { // scanner.nextLine();阻塞式的 String next = scanner.nextLine(); if (next.equals("exit")) { break; } allocate.put(next.getBytes()); allocate.flip(); open1.write(allocate); allocate.clear(); } open1.close(); } @Test public void serverSocketChannelTest() throws IOException { ServerSocketChannel open1 = ServerSocketChannel.open(); ByteBuffer allocate = ByteBuffer.allocate(1024); open1.bind(new InetSocketAddress(9898)); // 设置为非阻塞式 open1.configureBlocking(false); Selector selector = Selector.open(); // 将该通道注册到选择器上，SelectionKey.OP_ACCEPT 接收就绪：准备好接收新进入的连接 // 还有读就绪 ，写就绪，连接就绪 open1.register(selector, SelectionKey.OP_ACCEPT); while (true) { // selector.select() 阻塞式的方法，至少有一个通道被选择时才返回。当这个方法被执行时，当前线程是允许被中断 while (selector.select() > 0) { Set<SelectionKey> selectedKeys = selector.selectedKeys(); Iterator<SelectionKey> iterator = selectedKeys.iterator(); while (iterator.hasNext()) { SelectionKey key = iterator.next(); if (key.isAcceptable()) { SocketChannel channel = open1.accept(); channel.configureBlocking(false); channel.register(selector, SelectionKey.OP_READ); } else { SocketChannel channel = (SocketChannel) key.channel(); allocate.clear(); channel.read(allocate); allocate.flip(); System.out.println(new String(allocate.array())); } iterator.remove(); } } } }
8.DatagramChannel
@Test public void client() throws IOException{ DatagramChannel open = DatagramChannel.open(); open.configureBlocking(false); Scanner scanner = new Scanner(System.in); ByteBuffer allocate = ByteBuffer.allocate(1024); while(true){ String nextLine = scanner.nextLine(); if(nextLine.equals("exit")){ break; } allocate.put(new String("你好！").getBytes()); allocate.flip(); open.send(allocate, new InetSocketAddress("127.0.0.1", 9898)); allocate.clear(); } open.close(); } @Test public void server() throws IOException{ DatagramChannel open = DatagramChannel.open(); open.configureBlocking(false); open.bind(new InetSocketAddress(9898)); Selector select = Selector.open();
//没有SelectionKey.OP_ACCEPT open.register(select, SelectionKey.OP_READ); ByteBuffer allocate = ByteBuffer.allocate(1024); while(true){ //阻塞式 while(select.select()>0){ Set<SelectionKey> selectedKeys = select.selectedKeys(); Iterator<SelectionKey> iterator = selectedKeys.iterator(); while(iterator.hasNext()){ SelectionKey key = iterator.next(); if(key.isReadable()){ allocate.clear(); open.receive(allocate); allocate.flip(); System.out.println(new String (allocate.array())); } iterator.remove(); } } } } }
9.nio的锁（见后续juc）
lock：并且在获得锁之前，该线程将一直处于休眠状态。
tryLock：仅在调用时锁为空闲状态才获取该锁。如果锁可用则立即获取锁，返回true。如果锁不可用，则此方法返回false。
10.直接缓存区的map映射的分段读取（在物理内存不够用的情况的，或者严重影响效率的情况下）
public class SegmentDirTest { public static void main(String[] args) throws IOException { FileChannel open = FileChannel.open(Paths.get("1.txt"), StandardOpenOption.READ); FileChannel open1 = FileChannel.open(Paths.get("11.txt"), StandardOpenOption.READ, StandardOpenOption.WRITE, StandardOpenOption.CREATE); // position开始位置, size大小 MappedByteBuffer map = open.map(MapMode.READ_ONLY, 0, 2); // System.out.println(map.position());//0 open1.write(map); map.clear(); map = open.map(MapMode.READ_ONLY, 2, open.size() - 2); open1.write(map); open.close(); open1.close(); } }
