《Java基础知识》Java IO流详解

时间:2023-11-21 12:30:38

Java IO概念

1. 用于设备之间的数据传输。

2. Java 将操作数据流的功能封装到了IO包中。

3. 数据流流向分:输入流和输出流,操作对象为文件。

4. 流按照操作数据分:字节流(通用)和字符流。

5. 将计算机语言:二进制数据转换成文件显示到电脑上。

IO包:继承关系图:

《Java基础知识》Java IO流详解

字符流:

Reader :读取字符流,方法见API。

Writer :写入字符流,方法见API。

案例(Writer ):

import java.io.*;

public class var {
public static void main(String[] agrs){
Writer writer = null;
try{
writer = new FileWriter("Demo.txt");
// writer = new FileWriter("Demo.txt",true); 文件续写功能,否则会覆盖。
writer.write("今天天气真好!");
writer.flush();
} catch (IOException e) {
e.printStackTrace();
}finally {
if(writer != null){
try {
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}

运行结果:

《Java基础知识》Java IO流详解

案例(Reader):

文件数据:

《Java基础知识》Java IO流详解

import java.io.*;

public class var {
public static void main(String[] agrs){
Reader reader = null;
try{
reader = new FileReader("Demo.txt");
char[] arr = new char[5];
int red = reader.read(arr); //red是装到数组的长度。
while(red != -1 ){
System.out.println(new String(arr,0,red));
red = reader.read(arr);
}
} catch (IOException e) {
e.printStackTrace();
}finally {
if(reader != null){
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}

运行结果:

《Java基础知识》Java IO流详解

实现一个完整的文件复制。

import java.io.*;

public class var {
public static void main(String[] agrs){
Reader reader = null;
Writer writer = null;
try{
reader = new FileReader("Demo.txt");
writer = new FileWriter("Dome1.txt"); //
char[] arr = new char[5];
int red = 0; //red是装到数组的长度。
while((red = reader.read(arr)) != -1 ){
writer.write(new String(arr,0,red));
writer.flush();
}
} catch (IOException e) {
e.printStackTrace();
}finally {
if(reader != null){
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(writer != null){
try {
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}

运行结果:

《Java基础知识》Java IO流详解

优化文件复制案例(缓冲流):

import java.io.*;

public class var {
public static void main(String[] agrs){
BufferedReader bufferedReader = null; //缓冲读取流
BufferedWriter bufferedWriter = null; //缓冲写入流
try{
bufferedReader = new BufferedReader(new FileReader("Demo.txt"));
bufferedWriter = new BufferedWriter(new FileWriter("Dome2.txt"));
String str ;
while((str = bufferedReader.readLine()) != null ){
bufferedWriter.write(str);
bufferedWriter.newLine(); //换行。
bufferedWriter.flush();
}
} catch (IOException e) {
e.printStackTrace();
}finally {
if(bufferedReader != null){
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(bufferedWriter != null){
try {
bufferedWriter.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}

运行结果:

《Java基础知识》Java IO流详解

上述IO无法处理视频,图片等一些文件,拷贝出来的文件也无法打开,由此我们引出字节流。

字节流:

OutputSteam:写入字节流,方法见API。

InputSteam: 读取字节流,方法见API。

案例(OutputSteam):

public class var {
public static void main(String[] agrs){
FileOutputStream fileOutputStream = null;
try {
fileOutputStream = new FileOutputStream("demo.txt");
fileOutputStream.write("今天天气真好,我们去玩吧!".getBytes());
//不需要刷新。
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally {
if(fileOutputStream != null){
try {
fileOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}

运行结果:

《Java基础知识》Java IO流详解

案例(InputSteam):

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException; public class PublicTest {
public static void main(String[] args) {
FileInputStream fileInputStream = null;
try {
fileInputStream = new FileInputStream("demo.txt");
int ch =0;
byte[] arr = new byte[fileInputStream.available()]; //正式写代码不要使用fileInputStream.available(),因为文件比较大的时候内存会不够用。
while((ch = fileInputStream.read(arr)) != -1){
System.out.println(new String(arr,0,ch));
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(fileInputStream != null){
try {
fileInputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}

运行结果:

《Java基础知识》Java IO流详解

案例:复制一个视频文件

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException; public class PublicTest {
public static void main(String[] args) {
FileOutputStream fileOutputStream = null;
FileInputStream fileInputStream = null;
try {
fileInputStream = new FileInputStream("video.avi");
fileOutputStream = new FileOutputStream("video1.avi");
int ch =0;
byte[] arr = new byte[fileInputStream.available()]; //正式写代码不要使用fileInputStream.available(),因为文件比较大的时候内存会不够用。
while((ch = fileInputStream.read(arr)) != -1){
fileOutputStream.write(arr);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(fileInputStream != null){
try {
fileInputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(fileOutputStream != null){
try {
fileOutputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}

运行结果:

《Java基础知识》Java IO流详解

转换流(键盘输入和控制台输出作为案例):

import java.io.*;

public class var {
public static void main(String[] agrs){
OutputStream out = System.out; //控制台打印
OutputStreamWriter outputStreamWriter = null;
outputStreamWriter = new OutputStreamWriter(out); // outputStreamWriter = new OutputStreamWriter(out,"GBK"); 可以指定写的编码
BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter); InputStream in = System.in; //键盘输入流。
InputStreamReader inputStreamReader = new InputStreamReader(in); // InputStreamReader inputStreamReader = new InputStreamReader(in,"BGK"); 同样可以指定编码
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
try {
String line = null;
while((line = bufferedReader.readLine()) != null){
if("exit".equals(line)){
break;
}
bufferedWriter.write(line);
bufferedWriter.flush();
}
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
if(bufferedWriter != null){
bufferedWriter.close();
}
if(bufferedReader != null){
bufferedReader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

运行结果:

《Java基础知识》Java IO流详解

IO流先讲到这里,Java IO流还有很多有意思的类和方法见API。

参考:https://www.cnblogs.com/runningTurtle/p/7088125.html