FileInputStream讀：檔案——記憶體

兩個方法：

read();

read(byte[] buf);

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

/**
 * @author cuijiao
 * 
 */
public class IOStream {

    /**
     * @param args
     * @throws IOException
     */
    public static void main(String[] args) throws
 
 IOException {
        File file = new File("E:\\data\\logs\\homestay-error.log.2018-05-02");
        FileInputStream fis = new FileInputStream(file);
        int asc = -1;
        while ((asc = fis.read()) != -1) {// read()獲取的是位元組對應的ASC碼，一個位元組一個位元組的讀
            System.out.print((char) asc);
        }
        fis.close();// 關閉流
 

    }

}

一次性讀多個位元組，byte[]作為緩衝區暫存

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

/**
 * @author cuijiao
 *
 */
public class Filestream {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
 


        File file = new File("E:\\data\\logs\\udd-config-admin-error.log");
        FileInputStream fis = null;
        int lenth = -1;
        try {
            fis = new FileInputStream(file);
            byte[] buf = new byte[1024];// 儲存讀取資料的緩衝區。
            lenth = fis.read(buf);// read(byte[])返回讀入緩衝區的位元組總數，如果因為已經到達檔案末尾而沒有更多的資料，則返回 -1。
            while (lenth != -1) {// 讀到的資料（位元組）存在buf（緩衝區）裡了
                System.out.println(new String(buf, 0, lenth));// 讀字串string
                lenth = fis.read(buf);
            }
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            // finally塊中多放資源釋放相關程式碼
            try {// 關閉流，釋放記憶體
                if (fis != null) {
                    fis.close();
                    fis = null;
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }

}

FileOutputStream寫：記憶體——檔案

write（byte[] b）//清空重寫

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Scanner;

/**
 * @author cuijiao
 *
 */
public class Filestream {

    public static void main(String[] args) {

        File file = new File("D:\\data\\test.log");
        if (!file.exists()) {
            try {
                file.createNewFile();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream(file);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        Scanner sc = new Scanner(System.in);
        System.out.println("請輸入要寫入檔案的內容");
        String str = sc.nextLine();
        byte[] b = str.getBytes();
        try {
            fos.write(b);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            try {
                if (sc != null) {
                    sc.close();// 關閉鍵盤輸入
                    sc = null;
                }
                if (fos != null) {
                    fos.close();// 關閉輸出流
                    fos = null;
                }

            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }

}

FileInputStream、FileOutputStream結合使用實現檔案（圖片）的拷貝

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

/**
 * @author cuijiao
 *
 */
public class Filestream {

    public static void main(String[] args) throws IOException {

        File src = new File("D:\\data\\test.jpg");
        File target = new File("E:\\copy.jpg");
        copyFile(src, target);

    }

    /**
     * 拷貝檔案：將src複製到target
     *
     * @param src
     * @param target
     * @throws IOException
     */
    private static void copyFile(File src, File target) throws IOException {
        if (!src.exists()) {
            return;
        }
        if (!target.exists()) {
            target.createNewFile();
        }
        FileInputStream fis = null;
        FileOutputStream fos = null;

        fis = new FileInputStream(src);
        fos = new FileOutputStream(target);

        byte[] buf = new byte[1024];
        int lenth = -1;
        lenth = fis.read(buf);// 讀
        while (lenth != -1) {
            fos.write(buf, 0, lenth);// 寫
            lenth = fis.read(buf);// 讀
        }
        fis.close();
        fos.close();

    }

}