将数据写入指定文件
import lombok.extern.slf4j.Slf4j;
import java.io.File;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.StandardCharsets;
import java.nio.file.StandardOpenOption;
/**
* Created by lilinchao
* Date 2022/5/27
* Description channel Demo
*/
@Slf4j
public class channelDemo01 {
public static void main(String[] args) throws IOException {
// 获得一个根据指定文件路径的读写权限文件通道
FileChannel fileChannel = FileChannel.open(new File("datas/data.txt").toPath(), StandardOpenOption.WRITE,StandardOpenOption.READ);
//获得一段有指定内容的缓冲区
ByteBuffer source = ByteBuffer.wrap("helloWorld,Scala,Java".getBytes(StandardCharsets.UTF_8));
ByteBuffer target = ByteBuffer.allocate(50);
log.info("fileChannel.position():{}",fileChannel.position());
//将缓冲区中的内容写入文件通道
fileChannel.write(source);
//通道大小
log.info("fileChannel.position():{}", fileChannel.position());
//设置读写位置
fileChannel.position(0);
//将通道中的内容写到空缓冲区
fileChannel.read(target);
//转换缓冲区读写模式
target.flip();
log.info("target:{}", new String(target.array(), 0, target.limit()));
//关闭资源
fileChannel.close();
}
}
数据读写
import lombok.extern.slf4j.Slf4j;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.StandardCharsets;
/**
* Created by lilinchao
* Date 2022/5/27
* Description 数据读写
*/
@Slf4j
public class channelDemo02 {
public static void main(String[] args) throws IOException {
//获取输出流
FileOutputStream outputStream = new FileOutputStream("datas/data.txt");
//根据输出流获得一个"写"权限的通道
FileChannel outChannel = outputStream.getChannel();
//获得一个有指定内容的缓冲区
ByteBuffer source = ByteBuffer.wrap("HelloWorld".getBytes(StandardCharsets.UTF_8));
//将缓冲区内容写入到通道
outChannel.write(source);
//获取输入流
FileInputStream fileInputStream = new FileInputStream("datas/data.txt");
//根据输入流获得一个"读"权限的通道
FileChannel inChannel = fileInputStream.getChannel();
//获得一个空内容的缓冲区
ByteBuffer target = ByteBuffer.allocate(50);
//将通道中的内容读到缓冲区
inChannel.read(target);
//转换缓冲区读写模式
target.flip();
//读出缓冲区中的内容
log.info("target:{}", new String(target.array(), 0, target.limit()));
//关闭资源
outChannel.close();
inChannel.close();
}
}
超过 2g 大小的文件传输
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;
/**
* Created by lilinchao
* Date 2022/5/27
* Description 超过 2g 大小的文件传输
*/
public class TestFileChannelTransferTo {
public static void main(String[] args) {
try (
FileChannel from = new FileInputStream("datas/data.txt").getChannel();
FileChannel to = new FileOutputStream("datas/to.txt").getChannel()
) {
// 效率高，底层会利用操作系统的零拷贝进行优化
long size = from.size();
// left 变量代表还剩余多少字节
for (long left = size; left > 0; ) {
System.out.println("position:" + (size - left) + " left:" + left);
left -= from.transferTo((size - left), left, to);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
FileChannel Demo 改变子缓冲区内容
import java.io.File;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.IntBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.StandardCharsets;
/**
* Created by lilinchao
* Date 2022/5/27
* Description FileChannel Demo
*/
public class TestFileChannelDemo {
public static void main(String[] args) throws Exception {
// testSlice();
// testFileChannel();
// testIntBuffer();
// writeFileChannel();
testFileChannelTransfer();
}
/**
* 切片:改变缓冲区的内容
*/
public static void testSlice() throws Exception {
//获取通道
RandomAccessFile accessFile = new RandomAccessFile(new File("datas/data.txt"),"rw");
FileChannel channel = accessFile.getChannel();
//缓冲区
ByteBuffer buffer = ByteBuffer.allocate(9);
//将数据读入缓冲区
channel.read(buffer);
buffer.position(3);
buffer.limit(7);
//用于创建一个新的字节缓冲区，其内容是给定缓冲区内容的共享子序列。
ByteBuffer slice = buffer.slice();
//改变子缓冲区内容
for (int i = 0;i<slice.capacity();i++){
byte b = slice.get(i);
b *=2;
slice.put(i,b);
}
buffer.position(0);
buffer.limit(buffer.capacity());
while (buffer.remaining() > 0){
System.out.println(buffer.get());
}
}
/**
* fileChannel读文件
*/
public static void testFileChannel() throws Exception {
RandomAccessFile accessFile = new RandomAccessFile(new File("datas/data.txt"),"rw");
FileChannel channel = accessFile.getChannel();
//缓冲区
ByteBuffer buffer = ByteBuffer.allocate(1024);
//将数据读入缓冲区
//返回的值表示读取到的字节数，如果读到了文件末尾，返回值为 -1
int read = channel.read(buffer);
while (read != -1){
System.out.println("file长度:"+read);
buffer.flip();
while (buffer.hasRemaining()){
System.out.println((char) buffer.get());
}
//切换到写模式,position=0,limit变为capacity
buffer.clear();
read = channel.read(buffer);
}
accessFile.close();
System.out.println("end");
}
/**
* intBuffer
*/
public static void testIntBuffer(){
//用于在现有缓冲区旁边分配一个新的int缓冲区
IntBuffer buffer = IntBuffer.allocate(1024);
buffer.put(new int[]{1,2,3});
buffer.flip();
while (buffer.hasRemaining()){
System.out.println(buffer.get());
}
}
/**
* fileChannel写文件
*/
public static void writeFileChannel() throws Exception {
RandomAccessFile rw = new RandomAccessFile("datas/data.txt","rw");
FileChannel channel = rw.getChannel();
ByteBuffer buffer = ByteBuffer.allocate(1024);
buffer.put("欢迎来到李林超博客!!!".getBytes(StandardCharsets.UTF_8));
buffer.flip();
while (buffer.hasRemaining()){
channel.write(buffer);
}
channel.close();
}
//fileChannel通道之间传输
public static void testFileChannelTransfer() throws Exception {
RandomAccessFile accessFileA = new RandomAccessFile("datas/data.txt","rw");
FileChannel channelFrom = accessFileA.getChannel();
RandomAccessFile accessFileB = new RandomAccessFile("datas/dataB.txt","rw");
FileChannel channelTo = accessFileB.getChannel();
//from 的内容传输到 channelTo
channelTo.transferFrom(channelFrom,0,channelFrom.size());
accessFileA.close();
accessFileB.close();
}
}
附参考文章链接：
https://blog.csdn.net/qq_38745846/article/details/120786800
https://juejin.cn/post/7030802468552474637
