java的nio入门基础
Posted 白日梦
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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.Buffer
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
3.FileChannel
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();
}
}
4.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 } }
5.SocketChannel
待续
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