java筆記八：IO流之字符流與字符緩沖流

2019-11-17 03:27:27

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來源：轉載

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　　java中字符流主要都是繼承于Reader和Writer兩個抽象類。用于對字符文本的讀寫操作。

一、轉換類流

1 package com.iotest;
2
3 import java.io.FileInputStream;
4 import java.io.FileNotFoundException;
5 import java.io.FileOutputStream;
6 import java.io.IOException;
7 import java.io.InputStreamReader;
8 import java.io.OutputStreamWriter;
9
10 public class ConverseStreamDemo {
11
12     public static void main(String[] args) {
13         String s = "F://shar//test//test3.txt";
14         try {
15             //將字節流轉為字符流
16             OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream(s));
17             osw.write("中國北京");
18             System.out.PRintln(osw.getEncoding());
19             osw.close();
20             osw = new OutputStreamWriter(new FileOutputStream(s,true),"GB2312");
21             osw.write("中國北京");
22             System.out.println(osw.getEncoding());
23             osw.close();
24         } catch (FileNotFoundException e) {
25             // TODO Auto-generated catch block
26             e.printStackTrace();
27         } catch (IOException e) {
28             // TODO Auto-generated catch block
29             e.printStackTrace();
30         }
31         try {
32             //將字節流轉為字符流
33             InputStreamReader isr = new InputStreamReader(new FileInputStream(s),"GB2312");
34             int c;
35             while((c=isr.read()) != -1){
36                 System.out.print((char)c);
37             }
38             System.out.println();
39             isr.close();
40         } catch (FileNotFoundException e) {
41             // TODO Auto-generated catch block
42             e.printStackTrace();
43         } catch (IOException e) {
44             // TODO Auto-generated catch block
45             e.printStackTrace();

46 }
47 }
48
49 }

二、FileReader和FileWriter

1 package com.iotest;
2
3 import java.io.FileNotFoundException;
4 import java.io.FileReader;
5 import java.io.FileWriter;
6 import java.io.IOException;
7 /*
8 * 使用flush（）將流數據刷到目標里，這時流還存活著，還可以繼續使用該流進行別的操作。
9 * close（）雖然也有flush（）的效果但是這時流已經死了，你如果想繼續使用流的話就必須在此建立流
10 */
11 public class MutiplicationTable {
12
13     public static void main(String[] args) throws IOException {
14         String s = "F://shar//test//test5.txt";
15         FileWriter fw = new FileWriter(s);
16         FileReader fr = new FileReader(s);
17         for (int i = 1; i <= 9; i++) {
18             for (int j = 1; j <= i; j++) {
19                 String str = i + "*" + j + "=" + i*j + " ";
20                 fw.write(str);
21             }
22             fw.write("/r/n");
23             /*flush是指強行將輸出流中的數據寫到文件里面去。如果寫到這里的話就是一行一行的寫入文件
24              *最好每寫完一部分就刷新一次，如果最后刷新的話可能會造成數據的丟失
25              */
26             fw.flush();
27         }
28         //如果又不寫flush()又不寫close()，則不會寫入任何內容到文本里。只是寫到了緩沖區
29         //fw.flush(); 寫到這里的話就是所有的內容一起寫進文件
30         //fw.close(); close之前會調用flush()
31         //讀字符輸入流的數據
32         int c;
33         while ((c=fr.read())!=-1) {
34             System.out.print((char)c);
35         }
36     }
37
38 }

三、BufferedReader和BufferedWriter

1 package com.iotest;
2
3 import java.io.BufferedOutputStream;
4 import java.io.BufferedWriter;
5 import java.io.FileOutputStream;
6 import java.io.FileWriter;
7 import java.io.IOException;
8
9 public class PrimeNumber {
10     BufferedWriter bw = null;
11     String fileName = "F://shar//test//test7.txt";
12     //判斷是否是質數
13     public boolean isPrime(int n){
14         for(int i=2;i<=n/2;i++){
15             if(n%i == 0){
16                 return false;
17             }
18         }
19         return true;
20     }
21     void printPrime(int m) throws IOException{
22         //將字節流轉緩沖流
23         bw = new BufferedWriter(new FileWriter(fileName));
24         int j = 0;
25         for (int i = 2; i < m; i++) {
26             if(isPrime(i)){
27                 j++;
28                 String s = String.valueOf(i);
29                 String s1 = s + " ";
30                 bw.write(s1); //寫入文本文件
31                 if(j==10){
32                     j = 0;
33                     bw.newLine(); //寫入一個行分隔符
34                     bw.flush(); //強制刷新
35                 }
36             }
37         }
38
39         bw.close();
40     }
41     public static void main(String[] args) throws IOException {
42         PrimeNumber pn = new PrimeNumber();
43         pn.printPrime(100);
44     }
45
46 }

四、PrintWriter

1 package com.iotest;
2
3 import java.io.FileWriter;
4 import java.io.IOException;
5 import java.io.PrintWriter;
6
7 public class PrintWriterDemo {
8
9     public static void main(String[] args) throws IOException {
10         int A = 0; //千位
11         int B = 0; //百位
12         int C = 0; //十位
13         int num = 0;
14         String fileName = "F://shar//test//test8.txt";
15         FileWriter fw = new FileWriter(fileName); //字符輸出流
16         PrintWriter pw = new PrintWriter(fw);     //將字節輸出流轉為PrintWriter
17         for (int i = 1000; i < 10000; i++) {
18             A = i/1000;
19             B = i/100 % 10;
20             C = i/10 % 10;
21             if(i%11==0 && A == B+C){
22                 pw.print(i+" ");
23                 if(++num % 7 == 0){
24                     pw.println(); //寫入回車換行
25                     pw.flush();    //強制刷新流
26                 }
27             }
28         }
29         fw.close();
30
31     }
32
33 }

五、標準IO

1 package com.iotest;
2
3 import java.io.BufferedReader;
4 import java.io.FileWriter;
5 import java.io.IOException;
6 import java.io.InputStreamReader;
7 import java.io.PrintWriter;
8 import java.util.Scanner;
9
10 public class PackStardIO {
11
12     public static void main(String[] args) throws IOException {
13         BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
14         PrintWriter o = new PrintWriter(System.out); //包裝標準輸出
15         String s;
16         while((s=br.readLine())!=null && s.length()!=0){
17             o.println(s.toUpperCase());
18             //o.flush();   //一定要強制刷新讓其輸出來，否則不會輸出
19         }
20     }
21
22 }

1 package com.iotest;
2
3 import java.io.BufferedInputStream;
4 import java.io.BufferedOutputStream;
5 import java.io.BufferedReader;
6 import java.io.FileInputStream;
7 import java.io.FileNotFoundException;
8 import java.io.FileOutputStream;
9 import java.io.IOException;
10 import java.io.InputStreamReader;
11 import java.io.PrintStream;
12
13 public class StandardIORedirect {
14
15     public static void main(String[] args) throws IOException {
16         PrintStream console = System.out;
17         BufferedInputStream in = new BufferedInputStream(new FileInputStream("C://Documents and Settings//01//桌面//Test//src//com//iotest//StandardIORedirect.java"));
18         PrintStream out = new PrintStream(new BufferedOutputStream(new FileOutputStream("F://shar//test//test9.txt")));
19         System.setIn(in);     //對標準輸入流重定向
20         System.setOut(out);
21         System.setErr(out);
22         BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
23         String s;
24         while((s=br.readLine())!=null){   //從BufferedReader中讀取一行數據
25             System.out.println(s);
26         }
27         out.close();
28         System.setOut(console);
29     }
30
31 }

六、隨即訪問文件類

1 package com.iotest;
2
3 import java.io.FileNotFoundException;
4 import java.io.IOException;
5 import java.io.Random accessFile;
6
7 public class RandomRW {
8     public static void main(String[] args) throws IOException {
9         RandomAccessFile raf = new RandomAccessFile("F://shar//test//test10.dat","rw");
10         final int DOUBLE_SIZE = 8;
11         for (int i = 0; i < 10; i++) {
12             raf.writeDouble(i);
13             System.out.print(" " + (double)i);
14         }
15         System.out.println();
16         raf.close();
17         RandomAccessFile raf1 = new RandomAccessFile("F://shar//test//test10.dat","rw");
18         raf1.seek(3*DOUBLE_SIZE); //找到某個位置
19         raf1.writeDouble(300);     //往該位置插入數據
20         raf1.seek(5*DOUBLE_SIZE);
21         raf1.writeDouble(500);
22         raf1.close();
23         RandomAccessFile raf2 = new RandomAccessFile("F://shar//test//test10.dat","r");
24         for (int i = 0; i < 10; i++) {
25             System.out.print(" "+raf2.readDouble());
26         }
27         raf2.close();
28     }
29
30 }