java IO文件操作简单基础入门例子，IO流其实没那么难

Posted 2020-08-19 火凤凰

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IO是JAVASE中非常重要的一块，是面向对象的完美体现，深入学习IO，你将可以领略到很多面向对象的思想。
今天整理了一份适合初学者学习的简单例子，让大家可以更深刻的理解IO流的具体操作。

1、文件拷贝

try {

File inputFile = new File(args[0]);

if (!inputFile.exists()) {

System.out.println("源文件不存在，程序终止");

System.exit(1);

}

File outputFile = new File(args[1]);

InputStream in = new FileInputStream(inputFile);

OutputStream out = new FileOutputStream(outputFile);

byte date[] = new byte[1024];

int temp = 0;

while ((temp = in.read(date)) != -1) {

out.write(date);

}

in.close();

out.close();

} catch (FileNotFoundException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

2、java读文件:实现统计某一目录下每个文件中出现的字母个数、数字个数、空格个数及行数，除此之外没有其他字符

String fileName = "D:/date.java.bak";
        // String fileName = "D:/test.qqq";
        String line;
        int i = 0, j = 0, f = 0, k = 0;
        try {
            BufferedReader in = new BufferedReader(new FileReader(fileName));
            line = in.readLine();
            while (line != null) {
                // System.out.println(line);
                char c[] = line.toCharArray();
                for (int i1 = 0; i1 < c.length; i1++) {
                    // 如果是字母
                    if (Character.isLetter(c[i1]))
                        i++;
                    // 如果是数字
                    else if (Character.isDigit(c[i1]))
                        j++;
                    // 是空格
                    else if (Character.isWhitespace(c[i1]))
                        f++;
                }
                line = in.readLine();
                k++;
            }
            in.close();
            System.out
                    .println("字母:" + i + ",数字:" + j + ",空格:" + f + ",行数:" + k);
        } catch (IOException e) {
            e.printStackTrace();
        }
 
 
 
3、 从文件（d:\test.txt）中查出字符串”aa”出现的次数
 
try {
            BufferedReader br = new BufferedReader(new FileReader(
                    "D:\\test.txt"));
            StringBuilder sb = new StringBuilder();
            while (true) {
                String str = br.readLine();
                if (str == null)
                    break;
                sb.append(str);
            }
            Pattern p = Pattern.compile("aa");
            Matcher m = p.matcher(sb);
            int count = 0;
            while (m.find()) {
                count++;
            }
            System.out.println("\"aa\"一共出现了" + count + "次");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
 
 
 
 
4、 三种方法读取文件
try {
           // 方法一
           BufferedReader br = new BufferedReader(new FileReader(new File(
                   "D:\\1.xls")));
           // StringBuilder bd = new StringBuilder();
           StringBuffer bd = new StringBuffer();
           while (true) {
               String str = br.readLine();
               if (str == null) {
                   break;
               }
               System.out.println(str);
               bd.append(str);
           }
           br.close();
           // System.out.println(bd.toString());
           // 方法二
           InputStream is = new FileInputStream(new File("d:\\1.xls"));
           byte b[] = new byte[Integer.parseInt(new File("d:\\1.xls").length()
                   + "")];
           is.read(b);
           System.out.write(b);
           System.out.println();
           is.close();
           // 方法三
           Reader r = new FileReader(new File("d:\\1.xls"));
           char c[] = new char[(int) new File("d:\\1.xls").length()];
           r.read(c);
           String str = new String(c);
           System.out.print(str);
           r.close();
       } catch (RuntimeException e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       } catch (FileNotFoundException e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       } catch (IOException e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
 

5、三种方法写文件   
 
try {
           PrintWriter pw = new PrintWriter(new FileWriter("d:\\1.txt"));
           BufferedWriter bw = new BufferedWriter(new FileWriter(new File(
                   "d:\\1.txt")));
           OutputStream os = new FileOutputStream(new File("d:\\1.txt"));
           // 1
           os.write("ffff".getBytes());
           // 2
           // bw.write("ddddddddddddddddddddddddd");
           // 3
           // pw.print("你好sssssssssssss");
           bw.close();
           pw.close();
           os.close();
       } catch (IOException e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
 
 

[代码]6、读取文件，并把读取的每一行存入double型数组中
try {
            BufferedReader br = new BufferedReader(new FileReader(new File(
                    "d:\\2.txt")));
            StringBuffer sb = new StringBuffer();
            while (true) {
                String str = br.readLine();
                if (str == null) {
                    break;
                }
                sb.append(str + "、");
            }
            String str = sb.toString();
            String s[] = str.split("、");
            double d[] = new double[s.length];
            for (int i = 0; i < s.length; i++) {
                d[i] = Double.parseDouble(s[i]);
            }
            for (int i = 0; i < d.length; i++) {
                System.out.println(d[i]);
            }
            br.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }