Java中的IO流

Java中的4大IO抽象类

InputStream/OutputStream 为字节输入输出流

Reader/Writer 为字符输入输出流

InputStream

OutputStream

Reader

Writer

Java中流的概念细分

二进制文件（图片、影音）用字节流

文本信息用字符流

IO流的体系

练手案例

public class FirstDemo {public static void main(String[] args) throws IOException {// 创建字节输入流对象InputStream fileInputStream = new FileInputStream("D:\\桌面\\新建文本文档.txt");int s1;while ((s1 = fileInputStream.read())!=-1){System.out.println(s1);System.out.println((char)s1);}fileInputStream.close();}
}

File类

针对文件操作的方法

针对目录的方法

常用流对象

文件字节流

实现文件拷贝

public class Test {public static void main(String[] args) throws IOException {InputStream stream = new FileInputStream("D:\\桌面\\a.png");OutputStream outputStream = new FileOutputStream("D:\\桌面\\aa.jpg");int tem = 0;while((tem = stream.read()) != -1){System.out.println(tem);outputStream.write(tem);}outputStream.flush();stream.close();outputStream.close();}
}

通过缓冲区提高读写效率

方式一：

public class Test {public static void main(String[] args) throws IOException {InputStream stream = new FileInputStream("D:\\桌面\\a.png");OutputStream outputStream = new FileOutputStream("D:\\桌面\\aa.jpg");int tem = 0;byte[] buffer = new byte[1024];while((tem = stream.read(buffer)) != -1){  // 数组装满返回长度，装不满返回-1outputStream.write(buffer,0,tem);// 将buffer中0到tem的数据写入}outputStream.flush();stream.close();outputStream.close();}
}

方式二：

public class Test {public static void main(String[] args) throws IOException {InputStream stream = new FileInputStream("D:\\桌面\\a.png");OutputStream outputStream = new FileOutputStream("D:\\桌面\\aa.png");int tem = 0;byte[] buffer = new byte[stream.available()]; //  stream.available()是该文件的预估大小stream.read(buffer);outputStream.write(buffer);outputStream.flush(); // 将内存转入磁盘stream.close();outputStream.close();}
}

通过字节缓冲流提高效率

缓冲流为处理流

缓冲区中，默认有一个数组，默认为8192

public class Test {public static void main(String[] args) throws IOException {FileInputStream fis = new FileInputStream("D:\\桌面\\a.png");FileOutputStream fos = new FileOutputStream("D:\\桌面\\aa.png");BufferedInputStream bis  = new BufferedInputStream(fis);BufferedOutputStream bos = new BufferedOutputStream(fos);int tem = 0;while ((tem = bis.read()) != -1){bos.write(tem);}bos.flush();bos.close();bis.close();fis.close();fos.close();}
}

定义文件拷贝工具类

public static void copyFile(String src,String des) throws IOException {FileInputStream fis = new FileInputStream(src);FileOutputStream fos = new FileOutputStream(des);BufferedInputStream bis = new BufferedInputStream(fis);BufferedOutputStream bos = new BufferedOutputStream(fos);int temp = 0;while ((temp = bis.read()) != -1){bos.write(temp);}bos.flush();bis.close();bos.close();fis.close();fos.close();
}

文件字符流

文件字节流可以处理所有的文件，但是处理文本文件时，我们也可以使用文件字符流，他以字符为单位进行操作。

实现文件拷贝

public class readerwriter {public static void main(String[] args) throws IOException {FileReader fileReader = new FileReader("D:\\桌面\\a.txt");FileWriter fileWriter = new FileWriter("D:\\桌面\\aa.txt");int temp = 0;while ((temp = fileReader.read()) != -1){fileWriter.write(temp);}fileWriter.write("\r\n");// 回车换行fileWriter.write("hhhhhhhhhhhhhhhh");fileWriter.flush();FileWriter fileWriter2 = new FileWriter("D:\\桌面\\aa.txt",true); // 不加true默认覆盖，加了true为在尾部添加fileWriter2.write("houyiming");fileWriter2.flush();fileReader.close();fileWriter.close();fileWriter2.close();}
}

缓冲区提高效率

public class readerwriter {public static void main(String[] args) throws IOException {FileReader fileReader = new FileReader("D:\\桌面\\a.txt");FileWriter fileWriter = new FileWriter("D:\\桌面\\aa.txt");int temp = 0;char[] buffer = new char[1024];while ((temp = fileReader.read(buffer)) != -1){fileWriter.write(buffer,0,1024);}fileWriter.flush();fileReader.close();fileWriter.close();}
}

字符缓冲流

实现文件拷贝：

public class readerwriter {public static void main(String[] args) throws IOException {FileReader fileReader = new FileReader("D:\\桌面\\a.txt");FileWriter fileWriter = new FileWriter("D:\\桌面\\aa.txt");BufferedReader bufferedReader = new BufferedReader(fileReader);BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);String temp = "";while ((temp = bufferedReader.readLine()) != null){bufferedWriter.write(temp);bufferedWriter.newLine();}bufferedWriter.flush();bufferedReader.close();bufferedWriter.close();fileReader.close();fileWriter.close();}
}

转换流

public class ConvertStream {public static void main(String[] args) throws IOException {BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));String s = bufferedReader.readLine();BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(System.out));bufferedWriter.write(s);bufferedWriter.flush();bufferedReader.close();bufferedWriter.close();}
}

字节流读取文件并添加行号

public class ConvertStream {public static void main(String[] args) throws IOException {BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(new FileInputStream("D:\\桌面\\a.txt")));BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("D:\\桌面\\aa.txt")));String s = "";int i = 1;while ((s = bufferedReader.readLine()) != null){bufferedWriter.write(i+++"： "+s);bufferedWriter.newLine();}bufferedWriter.flush();bufferedWriter.close();bufferedWriter.close();}
}

字符输出流

节点流。

加行号：

public class ConvertStream {public static void main(String[] args) throws IOException {BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(new FileInputStream("D:\\桌面\\a.txt")));PrintWriter printWriter = new PrintWriter("D:\\桌面\\aa.txt");String s = "";int i = 1;while ((s = bufferedReader.readLine()) != null){printWriter.println(i+++": "+s);}printWriter.close();bufferedReader.close();}
}

字节数组流

public static void main(String[] args) throws IOException {byte[] bytes = "abcdefg".getBytes();ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(bytes);StringBuilder stringBuilder = new StringBuilder();//stringBuilder可以使用append的方法不断地添加元素创建字符串int temp = 0;while ((temp = byteArrayInputStream.read()) != -1){stringBuilder.append((char)temp);}System.out.println(stringBuilder.toString());
}

public static void main(String[] args) throws IOException {ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();byteArrayOutputStream.write('a');byteArrayOutputStream.write('b');byteArrayOutputStream.write('c');byte[] arr = byteArrayOutputStream.toByteArray();for (int i = 0; i < arr.length; i++) {System.out.println(arr[i]);}
}

数据流

public static void main(String[] args) throws IOException {DataOutputStream dos = new DataOutputStream(new BufferedOutputStream(new FileOutputStream("D:\\桌面\\a1.txt")));dos.writeInt(1);dos.writeChar('a');dos.writeDouble(9.99);dos.writeUTF("houyiming");dos.flush();dos.close();DataInputStream dis = new DataInputStream(new BufferedInputStream(new FileInputStream("D:\\桌面\\a1.txt")));// 注意：读取的顺序要与写入的顺序一致。System.out.println(dis.readInt());System.out.println(dis.readChar());System.out.println(dis.readDouble());System.out.println(dis.readUTF());
}

对象流

对象的序列化和反序列化

序列化：将java对象转化为字节序列

反序列化：将字节序列还原为java对象

操作基本数据类型

之前学的数据流只能对基本数据类型进行操作，但是对象流不仅可以操作基本数据类型，还可以操作Java对象。

public static void main(String[] args) throws IOException {ObjectOutputStream objectOutputStream = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream("D:\\桌面\\a1.txt")));objectOutputStream.writeInt(1);objectOutputStream.writeBoolean(true);objectOutputStream.writeChar('a');objectOutputStream.writeUTF("aaaaaaaaaaa");objectOutputStream.flush();ObjectInputStream objectInputStream = new ObjectInputStream(new BufferedInputStream(new FileInputStream("D:\\桌面\\a1.txt")));// 读出的顺序要与写入的顺序一致System.out.println(objectInputStream.readInt());System.out.println(objectInputStream.readBoolean());System.out.println(objectInputStream.readChar());System.out.println(objectInputStream.readUTF());objectInputStream.close();objectOutputStream.close();
}

操作对象

public static void main(String[] args) throws IOException, ClassNotFoundException {ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream("D:\\桌面\\a2.txt"));Users users = new Users(1,"hym","22");objectOutputStream.writeObject(users); // 序列化到外部objectOutputStream.flush();ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream("D:\\桌面\\a2.txt"));// 反序列化Users users1 = (Users) objectInputStream.readObject();System.out.println(users1.toString());objectInputStream.close();objectOutputStream.close(); 
}

随机访问流

3个核心的方法：

public static void main(String[] args) throws IOException, ClassNotFoundException {RandomAccessFile randomAccessFile = new RandomAccessFile("D:\\桌面\\aa.txt","rw");// 将数据写入文件int[] ints = new int[]{1,2,3,4,5,6,7,8,9,10};for (int i = 0; i < ints.length; i++) {randomAccessFile.writeInt(ints[i]);}randomAccessFile.seek(4);//整数占4个字节，将指针移动到4，为2的第一个字节。System.out.println(randomAccessFile.readInt());// 在第八个字节位置替换randomAccessFile.seek(8);randomAccessFile.writeInt(33);randomAccessFile.close();
}

ApacheIO包

下载与添加commons-IO包

下载地址：Commons IO – Download Apache Commons IO

选择commons-io-2.11.0.jar加入即可

这个地方显示即为成功

FileUtils的使用

读取txt文件并以字符串形式输出：

public static void main(String[] args) throws IOException {String s = FileUtils.readFileToString(new File("D:\\桌面\\a.txt"),"utf-8");System.out.println(s);
}

IOUtils的使用

toString方法的使用：

public static void main(String[] args) throws IOException {String s = IOUtils.toString(new FileInputStream("d:\\桌面\\a.txt"),"utf-8");System.out.println(s);
}

总结