第19天-11-IO流(字节流File读写操作)
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
/*
字符流
Reader/Writer
FileReader/FileWriter
BufferedReader/BufferedWriter
字节流:
InputStream/OutputStream
FileInputStream/FileOutputStream
需求:想要操作图片数据,这时就要用到字节流
*/
public class FileStream {
public static void main(String[] args) throws IOException {
// writeFile();
readFile_2();
}
public static void writeFile() throws IOException {
FileOutputStream fos = new FileOutputStream("fos.txt");
fos.write("abc厉害".getBytes());
// 写需要close无需flush -- 字符流底层也是一个字节一个字节进行操作,但是需要读取若干个字节,然后查码表输出字符,所以涉及缓存和flush.而字节流就不需要缓存也就无需flush
fos.close();
}
public static void readFile_0() throws IOException {
FileInputStream fis = new FileInputStream("fos.txt");
// 一个字节一个字节读
int ch;
while ((ch = fis.read()) != -1) {
System.out.println((char) ch);
}
fis.close();
}
public static void readFile_1() throws IOException {
FileInputStream fis = new FileInputStream("fos.txt");
byte[] buf = new byte[1024];// 1024*N 是字节数组合适的大小
int len;
while ((len = fis.read(buf)) != -1) {
System.out.println(new String(buf, 0, len, "utf-8"));
System.out.println(new String(buf, 0, len));
}
fis.close();
}
// 字节流特有的available()方法
public static void readFile_2() throws IOException {
FileInputStream fis = new FileInputStream("fos.txt");
// int available() 返回下一次对此输入流调用的方法"可以不受阻塞地从'此输入流'读取（或跳过）的估计剩余字节数"(含换行符)
// 如果new一个容量大小恰好为剩余文件字节数的byte[fis.available()],就无需循环而一次读完.但文件体积很大的情况下byte[]申请内存会失败
byte[] buf = new byte[fis.available()];
fis.read(buf);
System.out.println(new String(buf));
fis.close();
}
}
第19天-12-IO流(拷贝图片)
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
/*
拷贝一个图片,思路:
1.用字节读取流对象和源图片关联
2.用字节写入流对象创建一个图片文件,用于存储获取到的图片数据.
3.通过循环读写,完成数据的存储
4.关闭资源
*/
public class CopyPic {
public static void main(String[] args) {
FileOutputStream fos = null;
FileInputStream fis = null;
try {
fos = new FileOutputStream("2.png");
fis = new FileInputStream("1.png");
byte[] buf = new byte[1024];
int len;
while ((len = fis.read(buf)) != -1) {
fos.write(buf, 0, len);
}
} catch (Exception e) {
throw new RuntimeException("复制文件失败");
} finally {
try {
if (fis != null) fis.close();
} catch (IOException e) {
throw new RuntimeException("读取流关闭失败");
}
try {
if (fos != null) fos.close();
} catch (IOException e) {
throw new RuntimeException("输出流关闭失败");
}
}
}
}
第19天-13-IO流(字节流的缓冲区)
import java.io.*;
/*
演示mp3的复制(现在都不听mp3了,用图片代替),使用缓冲区.
BufferedInputStream/BufferedOutputStream
*/
public class CopyMp3 {
public static void main(String[] args) throws IOException {
long start = System.currentTimeMillis();
copy_1();
long end = System.currentTimeMillis();
System.out.println((end - start) + "ms");
}
public static void copy_1() throws IOException {
BufferedInputStream bufis = new BufferedInputStream(new FileInputStream("1.png"));
BufferedOutputStream bufos = new BufferedOutputStream(new FileOutputStream("3.png"));
int by;
while ((by = bufis.read()) != -1) {
bufos.write(by);
}
bufis.close();
bufos.close();
}
}
第19天-14-IO流(自定义字节流的缓冲区-read和write的特点)
import java.io.*;
public class MyBufferedInputStream {
private byte[] buf = new byte[1024];
private int pos, count;
private InputStream in;
public MyBufferedInputStream(InputStream in) {
this.in = in;
}
// 一次读一个字节,从缓冲区(字节数组)获取
public int myRead() throws IOException {
if (count == 0) { // count == 0表示数组中的元素已经被全部取走,需要再次进行read(buf)
if ((count = in.read(buf)) < 0) return -1;
//通过in对象读取硬盘上的数据,并存储至buf中,count也被重置为数组被填充的长度;如果in.read(buf)返回-1,表示in对象已经读取完毕
pos = 0; // 重置数组指针到0,开始重新读取
byte b = buf[pos];
count--;
pos++;
return b & 0xff; // 读取的类型byte b,返回值向上转换为int b
} else if (count > 0) {
byte b = buf[pos];
count--;
pos++;
return b & 0xff;
}
return -1;
}
public void myClose() throws IOException {
in.close();
}
public static void copy() throws IOException {
MyBufferedInputStream bufis = new MyBufferedInputStream(new FileInputStream("1.png"));
BufferedOutputStream bufos = new BufferedOutputStream(new FileOutputStream("3.png"));
int by;
while ((by = bufis.myRead()) != -1) {
bufos.write(by); // 传入的类型为int,实际上写入的是byte,多余的高位被截去
}
bufos.close();
bufis.myClose();
}
public static void main(String[] args) throws IOException {
long start = System.currentTimeMillis();
copy();
long end = System.currentTimeMillis();
System.out.println(end - start + "ms");
}
}