java IO文件操作入门经典例子

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。

在公司没活干，复习了一下IO，发现很多都忘记了，所以写的不好，只够初学用。我把我复习过程中写的代码贴出来，大家共同学习，并请多指教指教哈。顺便一起讨论IO

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();
}

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();
}