Java文件处理详解

Java文件处理是什么？极悦小编来为大家进行详细介绍。

1.文件操作

import java.io.File;
import java.io.IOException;
public class FileDemo {
    public static void main(String[] args) {
        File file1 = new File("./src/main/resources/test");
        File file2 = new File("./src/main/resources/test/score.txt");
        System.out.println(file1.isDirectory());
        System.out.println(file2.isFile());
        System.out.println(file1.isAbsolute());
        if (! file1.exists()) {
            file1.mkdirs();
        }
        if (! file2.exists()) {
            try {
                file2.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

2.字节流

字节输入流InputStream

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
/**
 * 从文件系统中的某个文件中获得输入字节
 * 用于读取诸如图像数据之类的原始字节流
 */
public class FileInputStreamDemo {
    public static void main(String[] args) {
        FileInputStream fis = null;
        try {
             fis = new FileInputStream("./src/main/resources/test/score.txt");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        if (fis != null) {
            // readDemo(fis);
            readByteDemo(fis);
        }
    }
    /**
     * read(byte[] b)
     * read(byte[] b, int off, int len)
     * @param fis
     */
    public static void readByteDemo(FileInputStream fis) {
        byte[] b = new byte[100];
        try {
            fis.read(b, 0, 5);
            System.out.println(new String(b));
            fis.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    /**
     * read()
     * @param fis
     */
    public static void readDemo(FileInputStream fis) {
        try {
            int n = 0;
            while ((n = fis.read()) != -1) {
                System.out.print((char) n );
            }
            fis.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

字节输出流OutputStream

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class FileOutputStreamDemo {
    public static void main(String[] args) {
        String name = "./src/main/resources/test/score1.txt";
        FileOutputStream fos;
        FileInputStream fis;
        try {
            fos = new FileOutputStream(name, true);
            fis = new FileInputStream(name);
            fos.write(50);
            fos.write('a');
            System.out.println(fis.read());
            System.out.println((char) fis.read());
            fos.close();
            fos.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

3.文件复制

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class CopyFileDemo {
    public static void main(String[] args) {
        String path = "./src/main/resources/test/";
        String name = "111.jpeg";
        try {
            FileInputStream fis = new FileInputStream(path + name);
            FileOutputStream fos = new FileOutputStream(path + "copy" + name);
            int n = 0;
            byte[] b = new byte[1024];
            while ((n = fis.read(b)) != -1) {
                fos.write(b, 0, n);
            }
            fis.close();
            fos.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

4.文件操作缓冲区Buffered

import java.io.*;
/**
 *  缓冲输入流 BufferedInputStream
 *  缓冲输出流 BufferedOutputStream
 */
public class BufferedDemo {
    public static void main(String[] args) {
        String name = "./src/main/resources/test/score1.txt";
        try {
            FileOutputStream fos = new FileOutputStream(name);
            BufferedOutputStream bos = new BufferedOutputStream(fos);
            FileInputStream fis = new FileInputStream(name);
            BufferedInputStream bis = new BufferedInputStream(fis);
            long startTime = System.currentTimeMillis();
            bos.write(50);
            bos.write('a');
            bos.flush(); // 缓冲区未写满，调用该方法强制清空缓冲区并写入文件
            System.out.println(bis.read());
            System.out.println((char) bis.read());
            long endTime = System.currentTimeMillis();
            System.out.println(endTime - startTime);
            fos.close();
            bos.close();  // 也会强制清空缓冲区并写入文件
            fis.close();
            bis.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

5.字符流

字符输入流 Reader

字符输出流 Writer

6.字节字符转换流

InputStreamReader

OutputStreamWriter

import java.io.*;
public class ReaderDemo {
    public static void main(String[] args) {
        String name = "./src/main/resources/test/score.txt";
        String name1 = "./src/main/resources/test/score1.txt";
        try {
            FileInputStream fis = new FileInputStream(name);
            InputStreamReader isr = new InputStreamReader(fis, "GBK");
            BufferedReader br = new BufferedReader(isr);
            FileOutputStream fos = new FileOutputStream(name1);
            OutputStreamWriter osw = new OutputStreamWriter(fos, "GBK");
            BufferedWriter bw = new BufferedWriter(osw);
            int n = 0;
            char[] cbuf = new char[10];
           /* while ((n = isr.read()) != -1) {
                System.out.print((char) n);
            }*/
            /*while ((n = isr.read(cbuf)) != -1) {
                String s = new String(cbuf, 0, n);
                System.out.print(s);
            }*/
            while ((n = br.read(cbuf)) != -1) {
                // String s = new String(cbuf, 0, n);
                // osw.write(s);
                bw.write(cbuf, 0, n);
                bw.flush();
            }
            fis.close();
            fos.close();
            isr.close();
            osw.close();
            br.close();
            bw.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

7.对象序列化

步骤：

(1)创建一个类，继承Serializable接口;

(2)创建对象;

(3)将对象写入文件;

(4)从文件读取对象信息

对象输入流ObjectInputStream

对象输出流ObjectOutputStream

import java.io.*;
public class GoodsTest {
    public static void main(String[] args) {
        String name = "./src/main/resources/test/score.txt";
        Goods goods1 = new Goods("gd001", "电脑", 3000);
        try {
            FileOutputStream fos = new FileOutputStream(name);
            ObjectOutputStream oos = new ObjectOutputStream(fos);
            FileInputStream fis = new FileInputStream(name);
            ObjectInputStream ois = new ObjectInputStream(fis);
            // 将Goods对象写入文件
            oos.writeObject(goods1);
            oos.writeBoolean(true);
            oos.flush();
            // 读取对象
            Goods goods = (Goods) ois.readObject();
            System.out.println(goods);
            System.out.println(ois.readBoolean());
            fos.close();
            oos.close();
            fis.close();
            ois.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}
import java.io.Serializable;
public class Goods implements Serializable {
    private String goodsId;
    private String goodsName;
    private double price;
    public Goods(String goodsId, String goodsName, double price) {
        this.goodsId = goodsId;
        this.goodsName = goodsName;
        this.price = price;
    }
    public String getGoodsId() {
        return goodsId;
    }
    public void setGoodsId(String goodsId) {
        this.goodsId = goodsId;
    }
    public String getGoodsName() {
        return goodsName;
    }
    public void setGoodsName(String goodsName) {
        this.goodsName = goodsName;
    }
    public double getPrice() {
        return price;
    }
    public void setPrice(double price) {
        this.price = price;
    }
    @Override
    public String toString() {
        return "Goods{" +
                "goodsId='" + goodsId + '\'' +
                ", goodsName='" + goodsName + '\'' +
                ", price=" + price +
                '}';
    }
}