Java_IO操作
创建文件夹：file.mkdir()
CreatDirectoryDemo.java
package com.tianjf;
import java.io.File;
public class CreatDirectoryDemo {
public static void main(String[] args) {
String directoryName = "D:" + File.separator + "hello";
File file = new File(directoryName);
file.mkdir();
}
}
创建文件：file.createNewFile()
CreatFileDemo.javapackage com.tianjf;
import java.io.File;
import java.io.IOException;
public class CreatFileDemo {
public static void main(String[] args) {
String fileName = "D:" + File.separator + "hello.txt";
File file = new File(fileName);
try {
file.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}
}
}
判断指定路径是文件夹还是文件：file.isDirectory() / file.isFile()
IsDirectoryOrFileDemo.java
package com.tianjf;
import java.io.File;
public class IsDirectoryOrFileDemo {
public static void main(String[] args) {
String directoryName = "D:" + File.separator + "hello";
File file = new File(directoryName);
if (file.isDirectory()) {
System.out.println("是一个文件夹！");
} else {
System.out.println("不是一个文件夹！");
}
String fileName = "D:" + File.separator + "hello.txt";
file = new File(fileName);
if (file.isFile()) {
System.out.println("是一个文件！");
} else {
System.out.println("不是一个文件！");
}
}
}
删除文件：file.delete()
DeleteFileDemo.java
package com.tianjf;
import java.io.File;
public class DeleteFileDemo {
public static void main(String[] args) {
String fileName = "D:" + File.separator + "hello.txt";
File file = new File(fileName);
if (file.exists()) {
file.delete();
} else {
System.out.println("文件不存在");
}
}
}
列出所有文件夹名和所有文件名：file.list() / 列出所有文件夹路径和所有文件路径：file.listFiles()
ListFilesDemo.java
package com.tianjf;
import java.io.File;
public class ListFilesDemo {
public static void main(String[] args) {
String directoryName = "D:" + File.separator;
File file = new File(directoryName);
// 列出所有文件夹名和所有文件名
String[] arrStr = file.list();
for (int i = 0; i < arrStr.length; i++) {
System.out.println(arrStr[i]);
}
// 列出所有文件夹路径和所有文件路径
System.out.println("---------------------------------------");
File[] arrFile = file.listFiles();
for (int i = 0; i < arrFile.length; i++) {
System.out.println(arrFile[i]);
}
// 列出所有文件夹路径和所有文件路径
System.out.println("---------------------------------------");
File[] arrFileWithFilter = file.listFiles(new FilenameFilter() {// 内部类
@Override
public boolean accept(File f1, String name) {
return name.endsWith(".txt");
}
});
for (int i = 0; i < arrFileWithFilter.length; i++) {
System.out.println(arrFileWithFilter[i]);
}
}
}
写入字节流：FileOutputStream
FileOutputStreamDemo.java
package com.tianjf;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
public class FileOutputStreamDemo {
public static void main(String[] args) throws IOException {
/* 将一个字符串作为一个整体写入文件 */
String fileName01 = "D:" + File.separator + "hello01.txt";
File file01 = new File(fileName01);
String str01 = "你好";
byte[] bytes01 = str01.getBytes();
OutputStream out01 = new FileOutputStream(file01);
out01.write(bytes01);
// 刷新缓存，写文件，最好加上这样的一句话
out01.flush();
out01.close();
/* 将一个字符串一个字节一个字节的写入文件 */
String fileName02 = "D:" + File.separator + "hello02.txt";
File file02 = new File(fileName02);
String str02 = "你好";
byte[] bytes02 = str02.getBytes();
OutputStream out02 = new FileOutputStream(file02);
for (int i = 0; i < bytes02.length; i++) {
out02.write(bytes02[i]);
}
out02.flush();
out02.close();
/* 追加新内容到文件中 */
String str03 = "追加的内容";
byte[] bytes03 = str03.getBytes();
OutputStream out03 = new FileOutputStream(file02, true);
for (int i = 0; i < bytes03.length; i++) {
out03.write(bytes03[i]);
}
out03.flush();
out03.close();
}
}
读入字节流：FileInputStream
FileInputStreamDemo.java
package com.tianjf;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
public class FileInputStreamDemo {
public static void main(String[] args) throws IOException {
/** 知道文件大小的读取 */
/* 整个读取 */
String fileName = "D:" + File.separator + "hello01.txt";
File file = new File(fileName);
InputStream in = new FileInputStream(file);
byte[] bytes = new byte[(int) file.length()];
in.read(bytes);
in.close();
System.out.println(new String(bytes));
/* 一个字节一个字节读取 */
in = new FileInputStream(file);
bytes = new byte[(int) file.length()];
for (int i = 0; i < bytes.length; i++) {
bytes[i] = (byte) in.read();
}
in.close();
System.out.println(new String(bytes));
/** 不知道文件大小的读取，需要判断是否读到了结尾 */
/* 每次读取1KB */
in = new FileInputStream(file);
bytes = new byte[1024];
while (true) {
// 读取1KB的内容到数组中
int num = in.read(bytes);
// 返回-1则表示读到了结尾
if (num == -1) {
break;
}
// 将字节数组转换为字符串（index = 0， length = num）
String str = new String(bytes, 0, num);
System.out.println(str);
}
in.close();
/* 一个字节一个字节的读取 */
in = new FileInputStream(file);
bytes = new byte[1024];
int count = 0;
int tempByte = 0;
while ((tempByte = in.read()) != -1) {
bytes[count++] = (byte) tempByte;
}
in.close();
System.out.println(new String(bytes));
}
}
写入字符流：FileWriter
FileWriterDemo.java
package com.tianjf;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
public class FileWriterDemo {
public static void main(String[] args) throws IOException {
String fileName = "D:" + File.separator + "hello.txt";
File file = new File(fileName);
String str = "hello";
Writer out = new FileWriter(file);
out.write(str);
out.flush();
out.close();
/* 追加新内容到文件中 */
out = new FileWriter(file, true);
out.write("\r\n" + str);
out.flush();
out.close();
}
}
读入字符流：FileReader
FileReaderDemo.java
package com.tianjf;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.Reader;
public class FileReaderDemo {
public static void main(String[] args) throws IOException {
String fileName = "D:" + File.separator + "hello.txt";
File file = new File(fileName);
char[] chars = new char[100];
Reader in = new FileReader(file);
int count = in.read(chars);
in.close();
System.out.println("读入的长度为：" + count);
System.out.println("内容为：" + new String(chars, 0, count));
/* 依次读取，需要判断是否读到了结尾 */
chars = new char[100];
in = new FileReader(file);
int tempChar = 0;
count = 0;
while ((tempChar = in.read()) != -1) {
chars[count++] = (char) tempChar;
}
in.close();
System.out.println("内容为：" + new String(chars, 0, count));
}
}
使用字节流好还是字符流好？
答案是字节流。首先因为硬盘上的所有文件都是以字节的形式进行传输或者保存的，包括图片等内容。但是字符只是在内存中才会形成的，所以在开发中，字节流使用广泛。
缓冲区：BufferdReader
BufferdReaderDemo.java
package com.tianjf;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class BufferdReaderDemo {
public static void main(String[] args) throws IOException {
BufferedReader br = null;
BufferedWriter bw = null;
bw = new BufferedWriter(new FileWriter("D:" + File.separator + "hello.txt"));
br = new BufferedReader(new FileReader("D:" + File.separator + "hello.txt"));
String s = null;
for (int i = 1; i <= 100; i++) {
s = String.valueOf(Math.random());
bw.write(s);
// 写入一个行分隔符
bw.newLine();
}
bw.flush();
while ((s = br.readLine()) != null) {// BufferdReader方便的方法readLine()读一行
System.out.println(s);
}
bw.close();
br.close();
}
}
使用Scanner类从文件中读出内容
ScannerDemo.java
package com.tianjf;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class ScannerDemo {
public static void main(String[] args) throws FileNotFoundException {
File file = new File("d:" + File.separator + "hello.txt");
Scanner scanner = new Scanner(file);
while (scanner.hasNext())
{
System.out.println(scanner.next());
}
}
}