Java编程思想:NIO知识点
2024-09-01 00:55:11
import java.io.*; import java.nio.*; import java.nio.channels.FileChannel; import java.nio.charset.Charset; import java.util.*; public class Test { public static void main(String[] args) { // GetChannel.test(); // BufferToText.test(); // AvailableCharSets.test(); // GetData.test(); // IntBufferDemo.test(); // ViewBuffers.test(); // Endians.test(); // UsingBuffers.test(); LargeMapperFiles.test(); } } /* 将字节存放在ByteBuffer的方法: 1.通过put方法直接对它们进行填充,填入一个或多个字节,或基本数据类型 2.通过warp方法将已存在的字节数组包装到ByteBuffer中,一旦如此,就不需要复制 底层的数组,而是把它作为所产生的ByteBuffer的存储器,称之为数组支持的ByteBuff。 */ /* 1.对于只读操作,需要显示静态的allocate方法来分配ByteBuffer 2.对于read方法,调用read告知FileChannel向ByteBuffer存储字节后,需要调用缓冲器上 的flip,让它做好让别人读取字节的准备。 3.对于read方法,如果我们打算用缓冲器执行进一步的read操作,则我们必须调用clear方法 来为每一个read做好准备 */ class GetChannel { private static final int BSIZE = 1024; public static void test() { try { //FileOutputStream测试 FileChannel fc1 = new FileOutputStream("./src/data").getChannel(); fc1.write(ByteBuffer.wrap("Some test".getBytes())); fc1.close(); //FileInputStream测试 FileChannel fc2 = new FileInputStream("./src/data").getChannel(); ByteBuffer buff = ByteBuffer.allocate(BSIZE); fc2.read(buff); buff.flip(); /* 这个地方和下一个案例的需求是不同的: 这个案例中我需要将buff中的数据一个一个字符的打印出出来,get方法 就像迭代器中的next方法,每次调用时都会向后移动一个位置: while (buff.hasRemaining()) System.out.println((char)buff.get()); 下一个案例中,是从文件中读取,当文件所有内容都被读取后,调用read 放法,就会在buffer中存入一个-1的值: while (fc1.read(buffer) != -1) { buffer.flip(); fc2.write(buffer); buffer.clear(); } } */ while (buff.hasRemaining()) { System.out.println((char)buff.get()); } //RandomAccessFile测试 FileChannel fc3 = new RandomAccessFile("./src/data","rw").getChannel(); fc3.position(fc3.size()); fc3.write(ByteBuffer.wrap("Some more".getBytes())); fc3.close(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } class ChannelCopy { private static final int BSIZE = 1024; public static void test() { try{ FileChannel fc1 = new FileInputStream("./src/data").getChannel(); FileChannel fc2 = new FileOutputStream("./src/data").getChannel(); ByteBuffer buffer = ByteBuffer.allocate(BSIZE); /* FileChannel和ByteBuffer的使用逻辑: 1.得到FileChannel,也就是书中说的煤矿 2.建立ByteBuffer,也就是书中说的卡车 3.通知煤矿向卡车转载货物 4.使用卡车中的货物 5.清空卡车中的货物 */ while (fc1.read(buffer) != -1) { buffer.flip(); fc2.write(buffer); buffer.clear(); } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } /* 上一个案例并不是理想的使用方式,transferTo和transferFrom则允许我们将一个通道与 另一个通道直接相连 */ class TransferTo{ public static void test() { try{ FileChannel in = new FileInputStream("./src/data").getChannel(); FileChannel out = new FileOutputStream("./src/data").getChannel(); //将in中的位置为0,长度为in.size()的数据移动到out这个通道中 in.transferTo(0,in.size(),out); //将in中的位置为0,长度为in.size()的数据移动到out这个通道中 out.transferFrom(in,0,in.size()); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } class BufferToText { private static final int BSIZE = 1024; public static void test() { try { //第一步,打开一个文件向里面写点东西 FileChannel fc1 = new FileOutputStream("./src/data1").getChannel(); fc1.write(ByteBuffer.wrap("some text".getBytes())); fc1.close(); //第二步,读取这个文件,尝试使用buffer的asCharBuffer进行输出 FileChannel fc2 = new FileInputStream("./src/data1").getChannel(); ByteBuffer buffer = ByteBuffer.allocate(BSIZE); fc2.read(buffer); buffer.flip(); System.out.println("buffer.asCharBuffer(): "+buffer.asCharBuffer()); //第三步,使用系统默认的方式解码 buffer.rewind(); //移动光标到开始部分 String encoding = System.getProperty("file.encoding"); System.out.println("encoding: "+encoding); System.out.println("Decode use "+encoding+" :"+Charset.forName(encoding).decode(buffer)); //第四步,写入东西时指定编码方式 FileChannel fc3 = new FileOutputStream("./src/data2").getChannel(); fc3.write(ByteBuffer.wrap("some text".getBytes("UTF-16BE"))); fc3.close(); //第五步,将写入的东西读出来 FileChannel fc4 = new FileInputStream("./src/data2").getChannel(); ByteBuffer buffer4 = ByteBuffer.allocate(BSIZE); fc4.read(buffer4); buffer4.flip(); System.out.println("buffer4.asCharBuffer(): "+buffer4.asCharBuffer()); //第六步,使用CharBuffer进行写 FileChannel fc5 = new FileOutputStream("./src/data2").getChannel(); ByteBuffer buffer5 = ByteBuffer.allocate(24); buffer5.asCharBuffer().put("some Text"); fc5.write(buffer5); fc5.close(); //第七步,将写入的内容读出来 FileChannel fc6 = new FileInputStream("./src/data2").getChannel(); ByteBuffer buffer6 = ByteBuffer.allocate(BSIZE); fc6.read(buffer6); buffer6.flip(); System.out.println("buffer6.asCharBuffer(): "+buffer6.asCharBuffer()); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } class AvailableCharSets { public static void test() { SortedMap<String,Charset> charset = Charset.availableCharsets(); Iterator<String> iter_name = charset.keySet().iterator(); while (iter_name.hasNext()) { String charsetName = iter_name.next(); System.out.print(charsetName); Set<String> aliases= charset.get(charsetName).aliases(); Iterator<String> iter_alia = aliases.iterator(); if(iter_alia.hasNext()) System.out.print(":"); while (iter_alia.hasNext()) { System.out.print(iter_alia.next()+" "); } System.out.println(""); } } } class GetData{ private static final int BSIZE = 1024; public static void test() { ByteBuffer b = ByteBuffer.allocate(BSIZE); //b在创建是会自动分配0 int i = 0; while (i++ < b.limit()) { if (b.get() != 0) { System.out.println("not zero."); } } System.out.println("i = "+i); //存储并读取一个char b.rewind(); b.asCharBuffer().put("Hello"); char c; while ((c = b.getChar()) != 0) { System.out.print(c); } System.out.println(); //存储并读取一个short b.rewind(); b.asShortBuffer().put((short) 471142); System.out.println("b.getShort(): "+b.getShort()); //存储并读取一个int b.rewind(); b.asIntBuffer().put(992341); System.out.println("b.getInt(): "+b.getInt()); //存储并读取一个long b.rewind(); b.asLongBuffer().put(234141532234L); System.out.println("b.getLong(): "+b.getLong()); //存储并读取一个float b.rewind(); b.asFloatBuffer().put(23414.134f); System.out.println("b.getFloat(): "+b.getFloat()); //存储并读取一个double b.rewind(); b.asDoubleBuffer().put(234.1432234); System.out.println("b.getDouble(): "+b.getDouble()); } } class IntBufferDemo{ private static final int BSIZE = 1024; public static void test() { ByteBuffer b = ByteBuffer.allocate(BSIZE); IntBuffer ib = b.asIntBuffer(); ib.put(new int[]{1,2,3,4,5}); System.out.println(ib.get(3)); System.out.println(ib.get(4)); ib.put(3, 100); System.out.println(ib.get(3)); System.out.println(ib.get(4)); System.out.println("Setting a new limit before rewinding the buffer"); ib.flip(); while (ib.hasRemaining()) { int i = ib.get(); System.out.println(i); } } } class ViewBuffers { public static void test() { ByteBuffer b = ByteBuffer.wrap(new byte[]{0,0,0,0,0,0,0,'a'}); b.rewind(); System.out.println("ByteBuffer:"); while (b.hasRemaining()) { System.out.println(b.position()+"-->"+b.get()+"."); } b.rewind(); CharBuffer cb = b.asCharBuffer(); System.out.println("CharBuffer:"); while (cb.hasRemaining()) { System.out.println(cb.position()+"-->"+cb.get()+"."); } } } class Endians { public static void test() { ByteBuffer b = ByteBuffer.wrap(new byte[12]); b.asCharBuffer().put("abcdef"); System.out.println(Arrays.toString(b.array())); b.rewind(); b.order(ByteOrder.BIG_ENDIAN); b.asCharBuffer().put("abcdef"); System.out.println(Arrays.toString(b.array())); b.rewind(); b.order(ByteOrder.LITTLE_ENDIAN); b.asCharBuffer().put("abcdef"); System.out.println(Arrays.toString(b.array())); } } class UsingBuffers { private static void symmetricScramble(CharBuffer buffer) { while (buffer.hasRemaining()) { buffer.mark(); char c1 = buffer.get(); char c2 = buffer.get(); buffer.reset(); buffer.put(c2).put(c1); } } public static void test() { char[] data = "UsingBuffers".toCharArray(); ByteBuffer bb = ByteBuffer.allocate(data.length * 2); CharBuffer cb = bb.asCharBuffer(); cb.put(data); System.out.println(cb.rewind()); symmetricScramble(cb); System.out.println(cb.rewind()); symmetricScramble(cb); System.out.println(cb.rewind()); } } class LargeMapperFiles { private static final int length = 0X8FFFFFF; //128 MB public static void test() { try { MappedByteBuffer out = new RandomAccessFile("./src/data", "rw") .getChannel() .map(FileChannel.MapMode.READ_WRITE, 0,length); for (int i = 0; i < length; i++) { out.put((byte)'x'); } System.out.println("Finished writing..."); for (int i = length / 2; i < length / 2 + 6; i++) { System.out.println((char)out.get(i)); } } catch (IOException e) { e.printStackTrace(); } } }
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