木舟0基础学习Java的第十八天(IO流，字节流，字符流，缓冲)

IO流正常使用流程：1.抛异常 2.资源读写 3.关闭资源(从后往前关)

字节流：(拷贝推荐使用)

开发中一般不会抛出异常用try{}catch(){} 也不推荐字节流读中文

FileInputStream:读

         FileInputStream fs=new FileInputStream("e:/b.txt");//11111111为-1的补码 会认为已经读取完毕 如果用byte 会出现数据读取不完整int i=0;while((i=fs.read())!=-1){System.out.println((char)i);}//必须关闭资源fs.close();}

FileOutputStream:写

 public static void main(String[] args) throws Exception {//如果e盘下没有b.txt FileOutputStream会自己创建一个FileOutputStream fo=new FileOutputStream("e:/b.txt");//write 一次写出一个字节fo.write(99);//cfo.write(100);//dfo.close();//追加 true代表不覆盖文件中的旧数据 追加到文件末尾FileOutputStream fo1=new FileOutputStream("e:/b.txt",true);fo1.write(97);fo1.write(98);fo1.close();//连续写入FileOutputStream fo2=new FileOutputStream("e:/b.txt");String s="abcdefghijklmn";//String s="我爱学习";//1f`  字节流写中文会乱码for(int i=0;i<s.length();i++){char c = s.charAt(i);fo2.write(c);}fo2.close();}

读写案例

案例：字节拷贝(读一个字节写一个字节效率低)

   public static void main(String[] args) throws Exception {FileInputStream fs=new FileInputStream("e:/1.jpg");//读FileOutputStream out=new FileOutputStream("e:/cba/1.jpg");//写int i=0;//一边读一边写while((i=fs.read())!=-1){//每次读一个字节out.write(i);//每次写一个字节}//先关后面的 再关前面的 关两个out.close();fs.close();}

案例：字节数组拷贝(读总字节写总字节效率高)

开发中推荐数组长度byte[] b=new byte[1024*8];

声明一个用来记录读取有效长度的变量 int len=0;

public static void main(String[] args) throws Exception {FileInputStream in=new FileInputStream("e:/1.jpg");//读FileOutputStream out=new FileOutputStream("e:/cba/1.jpg");//写//创建字节数组byte[] b=new byte[1024*8];//开发中推荐 数组长度byte[] b=new byte[1024*8];int len=0;//声明一个用来记录读取有效长度的变量 int len=0;while((len=in.read(b))!=-1){System.out.println(len);out.write(b,0,len);}out.close();in.close();}

逻辑：

  public static void main(String[] args) throws Exception {FileInputStream in=new FileInputStream("e:/1.jpg");//读FileOutputStream out=new FileOutputStream("e:/cba/1.jpg");//写int available = in.available();//获取文件总字节数//创建字节数组byte[] b=new byte[available];//创建一个数组 长度是图片所有字节长度while(in.read(b)!=-1){out.write(b);}out.close();in.close();}

Buffered缓冲区：

 public static void main(String[] args) throws Exception {FileInputStream in=new FileInputStream("e:/cba/w.mp4");BufferedInputStream bis=new BufferedInputStream(in);//自带缓冲区 底层就是new byte[8192]FileOutputStream out=new FileOutputStream("e:/abc/w.mp4");BufferedOutputStream bos=new BufferedOutputStream(out);//先写到缓冲区 写满后一次性写到文件中int b=0;while((b=bis.read())!=-1){bos.write(b);}//关闭缓冲区 关闭缓冲区后会自动关闭 in和outbos.close();bis.close();}

数组和Buffered：（开发中推荐数组拷贝）

如果是8192字节大小数组比Buffered快一些因为读和写都是同一数组

但是Bufferde操作的是两个数组

关闭资源(close，flush)

close:关闭释放资源如果是带缓冲区的流对象不但会关闭流还会在关闭流之前刷新缓冲区但是关闭之后不能再写出

flush:用来刷新缓冲区刷新后可以再写出

开发中标准写法：

 public static void main(String[] args) {FileInputStream in=null;FileOutputStream out=null;try {in=new FileInputStream("e:/cba/w.mp4");out=new FileOutputStream("e:/abc/ww.mp4");int len=0;byte[] b=new byte[1024*8];while((len=in.read(b))!=-1){out.write(b,0,len);}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}finally {if(out!=null){//避免下面报空指针异常try {out.close();} catch (IOException e) {throw new RuntimeException(e);}}if(in!=null){try {in.close();} catch (IOException e) {throw new RuntimeException(e);}}}}

案例：用键盘录入数据写到硬盘（带缓冲区和不带缓冲区）

public static void main(String[] args) {Scanner sc=new Scanner(System.in);FileOutputStream out=null;try {out=new FileOutputStream("e:/cba/aaa.txt",true);while(true){System.out.println("请输入：");String s=sc.next();if(!s.equals("quit")){byte[] b=s.getBytes();out.write(b);}else{break;}}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}finally{if(out!=null){try {out.close();} catch (IOException e) {throw new RuntimeException(e);}}}}

public static void main(String[] args) {Scanner sc=new Scanner(System.in);FileOutputStream out=null;BufferedOutputStream bos=null;try {out=new FileOutputStream("e:/cba/bbb.txt");bos=new BufferedOutputStream(out);while(true){System.out.println("请输入：");String s=sc.next();if(!s.equals("puit")){byte[] b=s.getBytes();bos.write(b);bos.flush();//刷新缓冲区 及时把缓冲区数据刷入硬盘}else{break;}}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}finally{if(bos!=null){try {bos.close();} catch (IOException e) {throw new RuntimeException(e);}}}}

字符流：(纯文本时推荐使用)

不可以拷贝非纯文本文件

FileReader:读

 public static void main(String[] args) {FileReader r=null;try {r=new FileReader("e:/cba/a.txt");int a=0;while((a=r.read())!=-1){System.out.println((char)a);}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}finally{if(r!=null){try {r.close();} catch (IOException e) {throw new RuntimeException(e);}}}}

FileWrite:写

 public static void main(String[] args) {FileWriter w=null;try {w=new FileWriter("e:/cba/n.txt");String s="你好，我不好！";char[] c = s.toCharArray();//将字符转为字节存入char数组w.write(c);} catch (IOException e) {throw new RuntimeException(e);}finally{if(w!=null){try {w.close();} catch (IOException e) {throw new RuntimeException(e);}}}}

读写案例

案例：字符拷贝(效率低容易拷贝不完整)

public static void main(String[] args) {FileReader fr=null;FileWriter fw=null;try {fr=new FileReader("e:/cba/a.txt");fw=new FileWriter("e:/abc/b.txt");int a=0;while((a=fr.read())!=-1){fw.write(a);}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}finally{try {fw.close();} catch (IOException e) {throw new RuntimeException(e);}try {fr.close();} catch (IOException e) {throw new RuntimeException(e);}}}

案例：字符数组拷贝(效率高拷贝完整)

public static void main(String[] args) {FileReader fr=null;FileWriter fw=null;try {fr=new FileReader("e:/cba/a.txt");fw=new FileWriter("e:/abc/a.txt");char[] c=new char[1024*8];int len=0;while((len=fr.read(c))!=-1){fw.write(c,0,len);System.out.println(len);}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}finally{try {fw.close();} catch (IOException e) {throw new RuntimeException(e);}try {fr.close();} catch (IOException e) {throw new RuntimeException(e);}}

Buffered缓冲区：

BufferedReader

public static void main(String[] args) {FileReader fr=null;BufferedReader br=null;try {fr=new FileReader("e:/abc/a.txt");br=new BufferedReader(fr);String s=null;//br.readLine()方法 可以读取一行字符 但不包括换行符号while((s=br.readLine())!=null){System.out.println(s);}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}finally{try {br.close();} catch (IOException e) {throw new RuntimeException(e);}}}

BufferedWriter

 public static void main(String[] args) {FileWriter fw=null;BufferedWriter bw=null;try {fw=new FileWriter("e:/abc/ab.txt");bw=new BufferedWriter(fw);bw.write("你好");bw.write("\r\n");bw.write("早上好");bw.newLine();//写入一个可以跨平台的换行符 相当于bw.write("\r\n"); 推荐使用！！！bw.write("不好！");} catch (IOException e) {throw new RuntimeException(e);}finally{try {bw.flush();} catch (IOException e) {throw new RuntimeException(e);}}}

BufferedReader和BufferedWriter

 public static void main(String[] args){FileReader fr=null;BufferedReader br=null;FileWriter fw=null;BufferedWriter bw=null;try {fr=new FileReader("e:/abc/a.txt");br=new BufferedReader(fr);fw=new FileWriter("e:/cba/t.txt");bw=new BufferedWriter(fw);String s=null;while((s=br.readLine())!=null){bw.write(s);bw.flush();}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}finally{if(bw!=null){try {bw.close();} catch (IOException e) {throw new RuntimeException(e);}}if(br!=null){try {br.close();} catch (IOException e) {throw new RuntimeException(e);}}}}

将文本反转案例：

 public static void main(String[] args) {//将文本反转FileReader fr=null;BufferedReader br=null;FileWriter fw=null;BufferedWriter bw=null;try {fr=new FileReader("e:/abc/a.txt");br=new BufferedReader(fr);String s=null;StringBuffer sb=new StringBuffer();while((s=br.readLine())!=null){sb.append(s);sb.append("\r\n");}//反转sb.reverse();//System.out.println(sb);//将sb中的数据全部写入fw=new FileWriter("e:/abc/ccc.txt");bw=new BufferedWriter(fw);bw.write(sb.toString());bw.flush();} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}finally{if(bw!=null){try {bw.close();} catch (IOException e) {throw new RuntimeException(e);}}if(br!=null){try {br.close();} catch (IOException e) {throw new RuntimeException(e);}}}}