java中的IO:处理流的使用

目录

1.桥梁流
2.缓冲流
3.数据流
4.对象流
5.合并流

1.桥梁流

1)InputStreamReader是输入字节流通向输入字符流的桥梁,每次调用read()方法都会导致从底层输入流读取一个或多个字节.
2)OuputStreamWriter是输出字节流通向输出字符流的桥梁,每次调用write()方法都会导致在给定字符集上调用编码转换器.
3)桥梁流虽然是一种处理流,但可将其包装到缓冲流中,已提高效率.

2.缓冲流

缓冲流中比较常用的是BufferedReader和BufferedWriter,BufferedReader中提供了readLine()方法,实现了读取一行文本;BufferedWriter中提供了newLine()方法,实现了写入一个行分隔符.下面我们对java所有源文件内容进行读取搜索,输出包含1.8新特性的文件:

public class Buffer_Reader_Writer {

	public static void search(File file, String str) throws IOException {
		File[] files = file.listFiles();
		// 判断是否为文件夹,是则递归查找
		if (file.isDirectory() && files.length != 0) {
			for (File sub : file.listFiles()) {
				search(sub, str);
			}
		} else {
			// 构造缓存输入流并按行读取文件
			BufferedReader br = new BufferedReader(new FileReader(file));
			String temp = br.readLine();
			while (temp != null) {
				if (temp.contains(str)) {
					System.out.println(file.getAbsolutePath());
					break;
				}
				temp = br.readLine();
			}
			br.close();
		}
	}

	public static void main(String[] args) throws IOException {
		search(new File("c:\\Program Files\\java\\src1.8"), "@since 1.8");
	}
}

3.数据流

数据流允许应用程序以与机器无关方式从底层节点流中读写java基本数据类型和String类型.例:

public class DataStreamDemo {

	public static void write() throws Exception {
		DataOutputStream dos = new DataOutputStream(new FileOutputStream(new File("c:\\a.txt")));
		dos.writeInt(89);
		dos.writeFloat(3.14f);
		dos.writeBoolean(false);
		dos.writeUTF("Hello World");
		dos.close();
	}

	public static void read() throws Exception {
		DataInputStream dis = new DataInputStream(new FileInputStream(new File("c:\\a.txt")));
		System.out.println(dis.readInt());
		System.out.println(dis.readFloat());
		System.out.println(dis.readBoolean());
		System.out.println(dis.readUTF());
		dis.close();
	}

	public static void main(String[] args) throws Exception {
		write();
		read();
	}
}

注意:读的顺序需要与写的顺序保持一致.

4.对象流

ObjectOutputStream,通过writeObject()方法将java对象写入OutputStream,这个过程称为序列化,实现序列化的类必须实现Serializable接口;ObjectInputStream,通过readObject()方法将之前的对象进行反序列化.例:

public class ObjectStreamDemo {

	public static void write() throws Exception {
		A a1 = new A("a", new B(97));
		A a2 = new A("b", new B(98));
		B b1 = new B(100);
		ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("c:\\obj.txt"));
		oos.writeObject(a1);
		oos.writeObject(a2);
		oos.writeObject(b1);
		oos.close();
	}

	public static void read() throws Exception {
		ObjectInputStream ois = new ObjectInputStream(new FileInputStream("c:\\obj.txt"));
		A a3 = (A) ois.readObject();
		A a4 = (A) ois.readObject();
		B b2 = (B) ois.readObject();
		System.out.println(a3);
		System.out.println(a4);
		System.out.println(b2);
		ois.close();
	}

	public static void main(String[] args) throws Exception {
		write();
		read();
	}
}

class A implements Serializable {
	String name;
	B b;

	public A(String name, B b) {
		this.name = name;
		this.b = b;
	}

	public String toString() {
		return "name:" + name + "\t" + b.toString();
	}
}

class B implements Serializable {
	int age;

	public B(int age) {
		this.age = age;
	}

	public String toString() {
		return "age:" + new Integer(age).toString();
	}
}

运行结果:
name:a age:97
name:b age:98
age:100
并且在c盘目录下生成obj.txt文件.

5.合并流

SequenceInputStream,表示两个或多个输入流的逻辑串联,第一个输入流开始读取,直到到达包含的最后一个输入流的文件末尾为止.例:

public class Test {

	public static void main(String[] args) throws Exception {
		FileInputStream fis1 = new FileInputStream("c:\\sequence1.txt");
		FileInputStream fis2 = new FileInputStream("c:\\sequence2.txt");
		// 将fis1和fis2串联成sis
		SequenceInputStream sis = new SequenceInputStream(fis1, fis2);
		FileOutputStream fos = new FileOutputStream("c:\\sequence3.txt");
		int temp = 0;
		while ((temp = sis.read()) != -1) {
			fos.write(temp);
		}
		fis2.close();
		sis.close();
		fos.close();
	}
}