一、文件操作
1. File的構(gòu)造方法
- 允許傳入一個(gè)表示路徑的字符串，可以是絕對(duì)路徑也可以是相對(duì)路徑，內(nèi)部調(diào)用文件系統(tǒng)類的方法為File對(duì)象中的實(shí)例域初始化。
public File(String pathname)
- 允許傳入兩個(gè)字符串，由命名可以看出必然是可以拼接的。
public File(String parent, String child);
//使用字符串拼接方法
String parent;
String child;
public File(parent.concat(child));
- 傳入了一個(gè)File類的對(duì)象作為parent，其實(shí)在內(nèi)部還是將此parent.path的路徑值拿出來(lái)進(jìn)行拼接。
public File(File parent, String child);
2. 讀取文件的內(nèi)容（I / O流）
流的方向：參考的是自己的內(nèi)存空間
-
流 Stream: 統(tǒng)一管理數(shù)據(jù)的寫入和讀取 可以理解為一個(gè)接口
Stream 輸出流：從內(nèi)存空間將數(shù)據(jù)寫到外部設(shè)備（磁盤、硬盤、光盤）開(kāi)發(fā)者只需要關(guān)心將內(nèi)存里面的寫到流里面
-
輸入流 ：將外部數(shù)據(jù)寫到內(nèi)存中 開(kāi)發(fā)者只需要關(guān)心從流里面讀取數(shù)據(jù)
I / O
輸出流：OutputStream 字節(jié)流 Writer字符流
輸入流：InputStream 字節(jié)流 Reader 字符流
- I / O 流對(duì)象不屬于內(nèi)存對(duì)象 需要自己關(guān)閉
- OutputStream和 InputStream都是抽象類 不能直接使用
字節(jié)流操作
FileOutputStream ?/ ? FileInputStream
ObjectOutputStream? / ?ObjectInputStream
字符流操作
FileWriter? /? FileReader
IO流
創(chuàng)建文件:
public class MyClass {
public static void main(String[] args) throws IOException,ClassNotFoundException {
//創(chuàng)建文件 完整路徑
String path = "D:\\AndroidStudioProjects\\JavaCourse\\Java\\src\\main\\java\\day8";
//path/1.txt 拼接文件名
File file = new File(path.concat("\\1.txt"));
// File file = new File(path,("\\1.txt"));
//判斷是否存在
if (file.exists() == false){
//不存在就創(chuàng)建
file.createNewFile();
}
}
向文件中寫入字節(jié)流:
//向文件寫入數(shù)據(jù)--字節(jié)流
//1.創(chuàng)建文件輸出流對(duì)象
FileOutputStream fos = new FileOutputStream(file);
//2.調(diào)用Writer方法寫入
byte[] text = {'1','2','3','4'};
fos.write(text);
//3.操作完畢 需要關(guān)閉對(duì)象
fos.close();
讀取字節(jié)流:
//讀取數(shù)據(jù)
FileInputStream fis = new FileInputStream(file);
byte[] name = new byte[12];
int count = fis.read(name);
fis.close();
System.out.println(count+" "+new String(name));
向文件中寫入字符流:
//向文件寫入數(shù)據(jù)字符流
FileWriter fw = new FileWriter(file);
char[] name = {'安','卓','開(kāi)','發(fā)'};
fw.write(name);
fw.close();
讀取字符流:
FileReader fr = new FileReader(file);
char[] book = new char[4];
count = fr.read(book);
fr.close();
System.out.println(count+" "+new String(book));
保存對(duì)象:
注意：保存的對(duì)象必須實(shí)現(xiàn)Serializable接口，如果對(duì)象內(nèi)部還有屬性變量是其他類的對(duì)象，這個(gè)類也必須實(shí)現(xiàn)Serializable接口
import java.io.Serializable;
public class Person implements Serializable {
public String name;
public int age;
public Dog dog;
}
class Dog implements Serializable{
public String name;
}
向文件中保存對(duì)象:
//創(chuàng)建Dog的一個(gè)對(duì)象
Dog wc = new Dog();
wc.name = "旺財(cái)";
Person xw = new Person();
xw.name = "小王";
xw.age = 20;
xw.dog = wc;
OutputStream os = new FileOutputStream(file);
ObjectOutputStream oos = new
ObjectOutputStream(os);
oos.writeObject(xw);
oos.close();
從文件中讀取對(duì)象：
//從文件里讀取一個(gè)對(duì)象
InputStream is = new FileInputStream(file);
ObjectInputStream ois = new ObjectInputStream(is);
Person xw = (Person) ois.readObject();
System.out.println(xw.name+" "+xw.age+" "+xw.dog.name);
ois.close();
-
使?BufferedInputStream和BufferedOutputStream提?讀寫的速度
long start = System.currentTimeMillis();
String sourcePath = "C:\\Users\\gyl\\Desktop\\文件夾\\0602-tabbar\\0602-2-自定義tabbarController.mov";
String desPath = "D:\\AndroidStudioProjects\\JavaCourse\\Java\\src\\main\\java\\day8/2.mov";
//輸入流
InputStream is = new FileInputStream(sourcePath);
BufferedInputStream bis = new BufferedInputStream(is);
//輸出流
OutputStream os = new FileOutputStream(desPath);
BufferedOutputStream bos = new BufferedOutputStream(os);
byte[] in = new byte[1024];
int count = 0;
while ((count = bis.read(in)) != -1){
bos.write(in,0,count);
}
bis.close();
bos.close();
long end = System.currentTimeMillis();
System.out.println(end - start);
-
RandomAccessFile 隨機(jī)訪問(wèn)?件 使?seek定位訪問(wèn)的位置
RandomAccessFile
密碼解鎖Demo：
main:
public class MyClassTest {
public static void main(String[] args){
boolean logined =false;
//判斷是否已經(jīng)登錄
String password = FileOperation.instance.password;
if (password != null){
logined = true;
}
//提示用戶操作
String alert;
if (logined) {
alert = "請(qǐng)輸入密碼";
} else {
alert = "請(qǐng)?jiān)O(shè)置密碼";
}
System.out.println(alert);
String first = null;
int wrongTime = 3;
while (wrongTime > 0) {
//接收用戶輸入
Scanner scanner = new Scanner(System.in);
String inputPassword = scanner.next();
//判斷操作
if (logined) {
//已經(jīng)登陸過(guò) 直接比較
if (password.equals(inputPassword)) {
System.out.println("解鎖成功");
break;
} else {
System.out.println("解鎖失敗 請(qǐng)重新輸入");
wrongTime--;
}
}else{
//沒(méi)有登陸過(guò) 在設(shè)置密碼
//判斷是設(shè)置密碼的第一次還是第二次
if (first == null){
//第一次 保存第一次輸入的密碼
first = inputPassword;
System.out.println("請(qǐng)確認(rèn)密碼 ");
}else{
//第二次 比較兩次輸入的密碼是否相同
if (first.equals(inputPassword)){
System.out.println("設(shè)置密碼成功");
//保存設(shè)置的密碼
FileOperation.instance.save(first);
break;
}else{
System.out.println("兩次密碼不一致 請(qǐng)重新設(shè)置密碼:");
first = null;
wrongTime--;
}
}
}
scanner.nextLine();
}
}
}
FileOperation.java
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
public class FileOperation {
public static final String PATH = "/Users/pengxiaodong/Desktop/day1/java/src/main/java/day8/Demo/pwd.txt";
String password;
public static final FileOperation instance = new FileOperation();
private FileOperation(){
try {
load();
}catch (IOException e){
System.out.println("io 異常");
}
}
public void load() throws IOException {
FileInputStream fis = new FileInputStream(PATH);
byte[] pwd = new byte[4];
int count = fis.read(pwd);
if (count == -1){
password = null;
}else{
password = new String(pwd);
}
fis.close();
}
public void save(String password){
try {
FileOutputStream fos = new FileOutputStream(PATH);
fos.write(password.getBytes());
fos.close();
} catch (IOException e){
System.out.println("io異常");
}
}
}
心得體會(huì)：
??Fighting！Fighting！Fighting！
