本文深入探讨了Java中的IO流操作，包括字节流和字符流的使用方法，如FileInputStream、FileOutputStream、BufferedReader等。同时，详细讲解了序列化与反序列化的过程，以及transient关键字的作用。
目录
枚举类型
新建，在others搜索enum
//Color.java
package com.mcq;
public enum Color {
RED,YELLOW,BLACK,WHITE,GREEN;
}
package com.mcq;
public class EnumDemo {
public static void main(String[] args) {
Color color=Color.WHITE;//这里必须写Color.
switch (color){
case RED: //这里必须不写Color.
System.out.println("红色");
break;
case WHITE:
System.out.println("白色");
break;
case YELLOW:
System.out.println("黄色");
break;
case BLACK:
System.out.println("黑色");
break;
case GREEN:
System.out.println("绿色");
break;
}
}
}
File
绝对路径：以盘符开头的路径名
相对路径：相对于工程目录的路径
package com.mcq;
import java.io.File;
import java.io.IOException;
public class FileDemo {
public static void main(String[] args) throws IOException {
File file=new File("E:\\javademo");
System.out.println(file);//并不会创建
System.out.println(file.mkdir());//创建文件夹
//首次创建返回true，已经有的情况下返回false
File file2=new File("E:\\javademo\\a\\b");//注意都是双\
System.out.println(file2.mkdir());//只能一级一级的创建
System.out.println(file2.mkdirs());//多级文件夹
File file3=new File("E:\\javademo\\1.txt");
System.out.println(file3.createNewFile());
File file4=new File("aa");//相对路径
System.out.println(file4.mkdir());
//file的删除功能只能从最底下删一层,如果文件夹还有文件，即使是最后一级目录，也无法删除
System.out.println(file4.delete());
//renameTo
new File("vv.txt").createNewFile();
new File("vv.txt").renameTo(new File("gg.txt"));
//判断 isFile isDirectory
System.out.println(new File("gg.txt").isFile());
//长度 Bytes
System.out.println(new File("gg.txt").length());
}
}文件过滤
package com.mcq;
import java.io.File;
import java.io.FilenameFilter;
public class FileDemo2 {
public static void main(String[] args) {
File file = new File("E://");
String []list=file.list(new FilenameFilter() { //文件过滤
public boolean accept(File dir, String name) {
if(name.endsWith(".txt")){
return true;
}else
return false;
}
});
for(String string:list){
System.out.println(string);
}
}
}递归删除所有文件
package com.mcq;
import java.io.File;
import java.io.FilenameFilter;
public class FileDemo2 {
public static void main(String[] args) {
File file=new File("E:\\javademo");
delete(file);
}
public static void delete(File file){
if(file.isDirectory()){//如果是目录
File [] sub=file.listFiles();//获取子文件/目录
for(File file2:sub){
delete(file2);
}
}
file.delete();
}
}
IO流
字节流（最小单位是字节）
FileOutputStream
package com.mcq;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
public class IODemo {
public static void main(String[] args) throws IOException {
File file=new File("mm.txt");
file.createNewFile();
FileOutputStream fos=new FileOutputStream(file,true);//true表示可追加
fos.write("\nhello world".getBytes());
fos.close();
}
}FileInputStream
package com.mcq;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
public class IODemo {
public static void main(String[] args) throws IOException {
File file=new File("mm.txt");
FileInputStream fis=new FileInputStream(file);
int read=fis.read();//读一个字节，这里输出ASCII码
System.out.println(read);
int b=-1;
while((b=fis.read())!=-1){
System.out.println((char)b);
}
}
}高效的方法：
package com.mcq;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
public class IODemo {
public static void main(String[] args) throws IOException {
File file=new File("mm.txt");
FileInputStream fis=new FileInputStream(file);
/*
* 1.创建一个固定长度的字节数组
* 2.当返回!=-1的时候，每次都将固定长度的字节放入数组,放不满补0
*/
byte []bys=new byte[1024];
while(fis.read(bys)!=-1){
for(byte b:bys){
System.out.print((char)b);
}
}
}
}拷贝图片：
package com.mcq;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class CopyPictureDemo {
public static void main(String[] args) throws IOException {
FileInputStream fis=new FileInputStream(new File("C:/Users/Administrator/Desktop/照片/1518715908475.jpg"));
FileOutputStream fos=new FileOutputStream(new File("tourist.png"));
byte []b=new byte[1024];
int cnt=0;
while(fis.read(b)!=-1){
fos.write(b);
++cnt;
}
System.out.println(cnt);
}
}BufferedOutputStream
带缓冲的输出流，关闭前需要刷新(flush)，将缓冲区的内容刷到流中，上面两个不带缓冲的不需要刷新。
package com.mcq;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class BufferDemo {
public static void main(String[] args) throws IOException {
BufferedOutputStream bos=new BufferedOutputStream(new FileOutputStream(new File("mm.txt")));
bos.write("hello mm".getBytes());
bos.flush();//要flush才能写入文件
// bos.close();//close调用了flush
}
}BufferedInputStream
package com.mcq;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class BufferDemo {
public static void main(String[] args) throws IOException {
BufferedInputStream bis = new BufferedInputStream(new FileInputStream(
new File("mm.txt")));
// 第一种方法
// int b=0;
// while((b=bis.read())!=-1){
// System.out.print((char)b);
// }
// bis.close();
// 第二种方法
byte[] bys = new byte[1024];
int len = 0;
while ((len = bis.read(bys)) != -1) {
System.out.println(new String(bys, 0, len));
}
bis.close();
}
}效率比较
buffered n字节>n字节>buffer一个字节>一个字节
字符流
输入输出中文的时候很可能会产生问题，这时就需要用字符流，字符流每次处理的是字符。
使用哪种方案进行编码，就要使用那种方案进行解码，不一致就会出现乱码。
BufferedWriter
package com.mcq;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
public class OutputStreamWriterDemo {
public static void main(String[] args) throws IOException {
BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File("mm.txt"))));
bw.write("好的");
bw.flush();
bw.append("haha");
bw.flush();
bw.close();
}
}BufferedReader
.
复制文件：
package com.mcq;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
public class OutputStreamWriterDemo {
public static void main(String[] args) throws IOException {
BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File("gg.txt"))));
BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(new File("mm.txt"))));
String line=null;
while((line=br.readLine())!=null){
bw.write(line);
bw.newLine();//自己加一个换行，因为读入的时候遇到换行结束，换行符并没有读进去
bw.flush();
}
bw.close();
br.close();
}
}
序列化
//student.java
package com.mcq;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class ObjectStreamDemo {
public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {
// ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("student.ser"));
// oos.writeObject(new Student("小明",18));
// oos.close();
ObjectInputStream ois =new ObjectInputStream(new FileInputStream("student.ser"));
Student student=(Student)ois.readObject();
System.out.println(student);
}
}package com.mcq;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
public class ObjectStreamDemo {
public static void main(String[] args) throws FileNotFoundException, IOException {
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("student.ser"));
oos.writeObject(new Student("小明",18));
oos.close();
}
}反序列化
package com.mcq;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class ObjectStreamDemo {
public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {
// ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("student.ser"));
// oos.writeObject(new Student("小明",18));
// oos.close();
ObjectInputStream ois =new ObjectInputStream(new FileInputStream("student.ser"));
Student student=(Student)ois.readObject();
System.out.println(student);
}
}可序列化的类需要实现Serializable接口，并且自动生成一个seriaVersionUID,使用两种生成方式均可。
如果不生成seriaVersionUID,则在序列化后修改类，再反序列化的过程中会抛出异常。
package com.mcq;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class ObjectStreamDemo {
public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {
// ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("student.ser"));
// oos.writeObject(new Student("小明",18));
// oos.close();
ObjectInputStream ois =new ObjectInputStream(new FileInputStream("student.ser"));
Student student=(Student)ois.readObject();
System.out.println(student);
student.test();
}
}transient关键字
如果在序列化的过程中，有不想去序列化的成员变量，那么可以添加transient关键字来修饰。
语法：public transient String name;
不能用来修饰方法
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