IO流读写文件

一、FileOutputStream

FileOutputStream(File file);

FileOutputStream(String name);

FileOutputStream o = new FileOutputStream();//在springboot中如果只是写个文件名，那么它会生成在pom.xml同级目录下

如果指定了绝对路径就会生成绝对路径下

o.writer(97);输入的是ACSII码中的a

byte[] bytes = {1,2,3,4};

o.writer(bytes);//输出的也是ACSII码中的值

o.writer(bytes,0,2);从0开始写两个

对于追加写入，只要在构造参数中加入第二个参数为true即可

FileOutputStream写出数据时加上异常处理

FileOutputStream fos = null;

try{

fos = new FileOutputStream("a.txt");

fos.writer("java".getBytes());

}catch(FileNotFoundException e){

e.

}catch(IoException e){

e.

}

FileOutputStream和FileInputStream的读写（这里的缓冲区可以不要，因为缓冲区使用的是装饰者模式将inputStream读取的数据保存在内存中，加快读取效率）

FileInputStream in = new FileInputStream("a.pdf");

BufferedInputStream bufferedInputStream = new BufferedInputStream(in);

FileOutputStream out = new FileOutputStream(path +s +".pdf");

BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(out);

//创建一个缓冲区

byte buffer[] = new byte[1024];

//判断输入流中的数据是否已经读完的标识

int len = 0;

//循环将输入流读入到缓冲区当中，(len=in.read(buffer))>0就表示in里面还有数据

while((len=bufferedInputStream.read(buffer))!=-1){

//使用FileOutputStream输出流将缓冲区的数据写入到指定的目录(savePath + "\\" + filename)当中

bufferedOutputStream.write(buffer, 0, len);

}

//关闭输入流

in.close();

//关闭输出流

out.close();

二、String类中的编码和解码

String(byte[] bytes,String charsetName)//按指定的字符集解码成字符串

byte[] getBytes(String charsetName);//按指定的字符集编码成字节

三、转换流(适配器模式)

OutputStreamWriter

OutputStreamWriter(OutputStream out);根据默认的编码集把字节流转换成字符流

OutputStreamWriter(OutputStream out,String charsetName);根据指定的编码集把字节流转换成字符流

InputStreamReader(InputStream in);

InputStreamReader(InputStream in,String charsetName);

四、字符流的5种写数据方式

public void write(int c);

write(char[] chars);

write(char[] chars,int off,int len);

write(String str);

write(String str,int off,int len)

使用以上方法写的时候写进去不显示，因为文件存储基本单位是字节需要flush()

使用字符流读取数据的方式

FileReader fileReader = new FileReader("a.txt");

BufferedReader bufferedReader = new BufferedReader(fileReader);

FileWriter f = new FileWriter("b.txt",true);

BufferedWriter bufferedWriter = new BufferedWriter(f);

String s ;

while ((s= bufferedReader.readLine())!=null){

bufferedWriter.write(s);

bufferedWriter.newLine();

}

bufferedWriter.flush();

bufferedReader.close();

bufferedWriter.close();

不使用缓冲流读取

//int s;

/* while ((s=fileReader.read())!=-1){

f.write(s);

}

f.flush();

fileReader.close();

f.close();*/

五、内存操作流

int a = 0;

int b = 1;

int c = 2;

ByteArrayOutputStream bout = new ByteArrayOutputStream();

bout.write(a);

bout.write(b);

bout.write(c);

byte[] buff = bout.toByteArray();

for (int i = 0; i < buff.length; i++)

System.out.println(buff[i]);

ByteArrayInputStream bin = new ByteArrayInputStream(buff);

while ((b = bin.read()) != -1) {

System.out.println(b);

}

FileInputStream inputStream = new FileInputStream("a.txt");

ByteArrayOutputStream outStream = new ByteArrayOutputStream();

byte [] buffer = new byte[3];

int len = 0;

while( (len = inputStream.read(buffer)) != -1){

outStream.write(buffer, 0, len);

}

byte [] data = outStream.toByteArray();

//FileOutputStream fileOutputStream = new FileOutputStream("c.txt");

//byte [] data = "java".getBytes();

 

//ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(data);

//byte buffer1[] = new byte[1024];

//int b =0 ;

// while ((b = byteArrayInputStream.read(byffer1)) != -1) {

//System.out.println(b);

//fileOutputStream.write(buffer1,0,b);

// }

//fileOutputStream.close();

System.out.println(new String(data));

/* FileInputStream in = new FileInputStream("a.txt");

BufferedInputStream bufferedInputStream = new BufferedInputStream(in);*/

FileOutputStream out = new FileOutputStream("b.txt");

//BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(out);

/* byte [] data = "java".getBytes();

ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(data);

//创建一个缓冲区

byte buffer[] = new byte[1024];

//判断输入流中的数据是否已经读完的标识

int len = 0;

//循环将输入流读入到缓冲区当中，(len=in.read(buffer))>0就表示in里面还有数据

while((len=byteArrayInputStream.read(buffer))!=-1){

//使用FileOutputStream输出流将缓冲区的数据写入到指定的目录(savePath + "\\" + filename)当中

out.write(buffer, 0, len);

}*/

//关闭输入流

//in.close();

//关闭输出流

//out.close();

}