JAVA IO

字节流

1. FileInputStream  FileOutputStream通过字节流来读写文件

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1. public static void main(String[] args) throws Exception {  
2. //将文件里写数据
3.     File f = new File("d:\\dmeo.txt");  
4.     FileOutputStream output = new FileOutputStream(f);  
5.     String s = "I Am Learning Java , 我在学习Java";  
6. byte[] b = s.getBytes(); //将String变为byte数组
7. //output.write(b);write可以接收byte数组
8. for (int i = 0; i < b.length; i++) {  
9.         output.write(b[i]);  
10.     }  
11.     output.flush();  
12.     output.close();  
13. //读取文件里数据
14.     FileInputStream input = new FileInputStream(f);  
15. //开辟一个文件大小的数组空间
16. byte[] in = new byte[(int) f.length()];  
17. //将读取来的字节放入数组中
18. for (int i = 0; i < in.length; i++) {  
19.         in[i] = (byte) input.read();   
20.     }  
21.     System.out.print(new String(in));  
22.     input.close();  
23. } 

2. BufferedInputStream BufferedOutPutStream 带有缓存的读写字节流

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1. public static void main(String[] args) throws Exception {  
2. //将文件里写数据
3. File f = new File("d:\\dmeo.txt");  
4. BufferedOutputStream output = new BufferedOutputStream(new FileOutputStream(f));  
5. String s = "I Am Learning Java , 我在学习Java";  
6. byte[] b = s.getBytes();  
7. output.write(b); //默认会有512字节的缓存，当缓存存满时一次性向文件中写入
8. output.flush();   
9. output.close();  
11. BufferedInputStream input = new BufferedInputStream(new FileInputStream(f));  
12. byte[] in = new byte[(int)f.length()];  
13. for (int i = 0; i < in.length; i++) {  
14.         in[i] = (byte)input.read();  
15.     }  
16. System.out.println(new String(in));  
17. input.close();  
18. } 

2. DataInputStream DataOutputStream 可以读写基本数据类型的字节流

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1. import java.io.*;  
2. //一个简单的人员类，只有姓名和年龄
3. public class Person {  
4. private String name;  
5. private int age;  
7. public Person(String name ,int age){  
8. this.name = name;  
9. this.age = age;  
10.     }  
12. public String getName(){  
13. return this.name;  
14.     }  
15. public int getAge() {  
16. return this.age;  
17.     }  
20. public static void main(String[] args) {  
21. //构造对象数组
22.         Person[] p1 = {new Person("Ryan",20),new Person("Tom",30),new Person("Jerry",15)};  
23.         File f = new File("d:\\demo\\demo.txt");  
24. try {  
25.             DataOutputStream output =  new DataOutputStream(new FileOutputStream(f));  
26. //写入数据
27. for (int i = 0; i < p1.length; i++) {  
28.                 output.writeUTF(p1[i].getName()); //以UTF编码写入姓名
29.                 output.writeInt(p1[i].getAge()); //以Int型写入年龄
30.             }  
31.             output.flush();  
32.             output.close();  
33.         } catch (Exception e) {  
34.             e.printStackTrace();  
35.         }     
36.         Person[] p2 = new Person[p1.length];  
37. try {  
38. //读出数据
39.             DataInputStream input = new DataInputStream(new FileInputStream(f));  
40. for (int i = 0; i < p1.length; i++) {  
41.                 String name =  input.readUTF(); //读出姓名
42. int age  = input.readInt(); //读出年龄
43. //重新构造person对象
44.                 p2[i] = new Person(name,age);             
45.             }  
46.                 input.close();  
47.         } catch (Exception e) {  
48.             e.printStackTrace();  
49.         }  
50. //检查是否还原正确
51. for (int i = 0; i < p2.length; i++) {  
52.             System.out.println("姓名：" + p2[i].getName() + " ；年龄：" + p2[i].getAge());  
53.         }  
55.     }  
56. }<strong>  
57. </strong> 

2. PrintStream  将内存中的数据经过相应的转换后再输出

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1. public static void main(String[] args){  
2.     File f = new File("d:\\dmeo.txt");  
3.     String studentName = "TOM";  
4. int age = 20;  
5. double totalScore = 600.0f;  
6.     PrintStream ps = null;  
7. try {  
8.         ps = new PrintStream(new FileOutputStream(f));  
9.     } catch (FileNotFoundException e) {  
10.         e.printStackTrace();  
11.     }  
12. //格式化后输出
13.     ps.printf("姓名：%s , 年龄：%d , 总分：%3.1f",studentName,age,totalScore);  
14. }