Java Old IO
Java IO是通過Stream 以block方式讀取數據的。其中包括字節和字符Stream.
下面一個小例子，分別用字節和字符流來讀取文件。
import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
public class OldIOTest {
static String fileName="c:/test.txt";
private void readFileByByte(String fileName) {
BufferedInputStream bufferedInputStream = null;
try {
bufferedInputStream = new BufferedInputStream(new FileInputStream(new File(fileName)));
byte[] data = new byte[1024];
int len;
while ((len = bufferedInputStream.read(data)) > 0) {
System.out.println(new String(data, 0, len));
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (bufferedInputStream != null) {
try {
bufferedInputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
private void readFileByChar(String fileName) {
BufferedReader bReader= null;
try {
bReader=new BufferedReader(new FileReader(new File(fileName)));
String line;
while((line=bReader.readLine())!=null){
System.out.println(line);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally {
if(bReader!=null){
try {
bReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
public static void main(String[] args) {
OldIOTest oldIOTest = new OldIOTest();
oldIOTest.readFileByByte(fileName);
System.out.println("------------------------------------------");
oldIOTest.readFileByChar(fileName);
}
}
執行結果;
test java io
this is a test file.
------------------------------------------
test java io
this is a test file.
Java NIO
Java NIO 是通過Buffer以非block方式讀取數據的。NIO 將最耗時的 I/O 操作轉移回操作系統，因而可以極大地提高速度。
其中重要的幾個概念：
- Channels
- Buffers
- Selectors
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class NIOTest {
static String fileName = "c:/test.txt";
private void readFile(String fileName) {
try {
@SuppressWarnings("resource")
FileChannel channel = new FileInputStream(new File(fileName)).getChannel();
ByteBuffer buffer = ByteBuffer.allocate(64);
while (channel.read(buffer) != -1) {
buffer.flip();
while (buffer.hasRemaining()) {
System.out.print((char) buffer.get());
}
buffer.clear();
}
channel.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
private void write(String fileName) {
RandomAccessFile randomAccessFile = null;
try {
randomAccessFile = new RandomAccessFile(new File(fileName), "rw");
FileChannel channel = randomAccessFile.getChannel();
channel.position(randomAccessFile.length());
ByteBuffer buffer = ByteBuffer.allocate(64);
buffer.put("\nnew test.".getBytes());
buffer.flip();
channel.write(buffer);
channel.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
NIOTest nioTest = new NIOTest();
nioTest.write(fileName);
nioTest.readFile(fileName);
}
}
執行結果：
test java io
this is a test file.
new test.
參考：
http://tutorials.jenkov.com/java-nio/index.html
https://www.ibm.com/developerworks/cn/education/java/j-nio/j-nio.html
