6.4 通过IO实现文件的读取与写入
6.4 通过IO实现文件的读取与写入
- 1. File类及常用方法
- 2. 通过字节字符流实现文件读取与写入
-
- 1. 流
- 2. 字节输入输出流 InputStream与OutputStream
- 3. 字符输入输出流实现文本读取与写入
- 4. 字节流与字符流的相互转化
- 3. 缓冲区及应用
- 4. 其他流的应用
- 5. 练习:利用URLConnection对象下载网络图片
- 6. 总结
1. File类及常用方法
package com.imooc.io;
import java.io.File;
import java.io.IOException;
public class FileSample {
public static void main(String[] args) {
File f = new File("d:/b.txt");
File d = new File("d:/电影/华语/大陆");
try {
boolean r1 = f.createNewFile();
System.out.println(f.getPath() + "文件创建是否成功:" + r1);
System.out.println(f.getPath() + "是否存在：" + f.exists());
System.out.println(f.getPath() + "是否是目录：" + f.isDirectory());
System.out.println(f.getPath() + "是否是文件："+f.isFile());
System.out.println(f.getPath() + "的大小："+f.length());
System.out.println(f.getPath() + "的文件名："+f.getName());
boolean r2 = f.delete();
System.out.println(f.getPath() + "文件是否删除成功:" + r2);
System.out.println(f.getPath() + "是否存在："+ f.exists());
boolean r3 = d.mkdirs();
System.out.println("[" + d.getPath() + "]目录是否创建成功:" + r3);
}catch (IOException e){
e.printStackTrace();
}
}
}
2. 通过字节字符流实现文件读取与写入
1. 流
2. 字节输入输出流 InputStream与OutputStream
package com.imooc.io;
import java.io.*;
public class FileCopySample {
public static void main(String[] args) {
File source = new File("d:/demo.jpg");
File target = new File("d:/demo1.jpg");
InputStream fis = null;
OutputStream fos = null;
try {
//实例化InputStream对象:读文件
fis = new FileInputStream(source);
//实例化Outputstream对象:写文件
fos = new FileOutputStream(target);
byte[] bs = new byte[1024];
int len;
//利用read方法循环读取的字节数据，并进行处理
while((len = fis.read(bs)) != -1){
System.out.println(len);
//将读取到到字节数组写入到输出流
fos.write(bs,0,len);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally { //通过finally块确保fis/fos对象执行close方法
if(fos != null){
try {
fos.close();//关闭写
} catch (IOException e) {
e.printStackTrace();
}
}
if(fis != null){
try {
fis.close();//关闭读
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
3. 字符输入输出流实现文本读取与写入
package com.imooc.io;
import java.io.*;
public class TextFileSample {
/*FileReader读取文本文件案例*/
public void readTextFile(){
Reader reader = null;
try{
File file = new File("d:/test.txt");
//实例化Reader对象
reader = new FileReader(file);
int ch = 0;
//逐个字符读取
while((ch = reader.read()) != -1){
System.out.print((char)ch);//UTF-8编码集
}
}catch (IOException e){
e.printStackTrace();
}finally {
if(reader != null){
try {
//关闭reader对象
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
/*Writer写入文本文件过程*/
public void writeTextFile(){
Writer writer = null;
try {
File file = new File("d:/test.txt");
//创建文件
if (!file.exists()) {//判断文件是否存在
file.createNewFile();//不存在,创建对于文件
}
//实例化writer对象
writer = new FileWriter(file);
//write()方法用于覆盖已有文件内容
writer.write("这是一个新文件New");
//append()方法用于在文件末尾追加
writer.append(":Append内容");
}catch (IOException e){
e.printStackTrace();
}finally {
//关闭writer对象
if(writer != null){
try {
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
public static void main(String[] args) {
TextFileSample sample = new TextFileSample();
sample.writeTextFile();
sample.readTextFile();
}
}
4. 字节流与字符流的相互转化
了解即可
package com.imooc.io;
import java.io.*;
public class TextFileSample {
/**
* 字节转字符读取文件内容
* 字节输入流(InputStream)转字符输入流(InputStreamReader)
*/
public void isrSample(){
InputStream fis = null;
InputStreamReader isr = null;
try{
File file = new File("d:/test.txt");
fis = new FileInputStream(file);
isr = new InputStreamReader(fis,"UTF-8");
StringBuffer buffer = new StringBuffer();
while(isr.ready()){
buffer.append((char)isr.read());
}
System.out.println(buffer.toString());
}catch (IOException e){
e.printStackTrace();
}finally {
if(isr != null){
try {
isr.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if(fis != null){
try {
fis.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
/**
* 字节转字符写入文件内容
* 字节输出流(OutputStream)转字符输出流(OutputStreamWriter)
*/
public void oswSample() {
OutputStream fos = null;
OutputStreamWriter osw = null;
try {
File file = new File("D:/test.txt");
//创建文件
if (!file.exists()) {
file.createNewFile();
}
fos = new FileOutputStream(file);
osw = new OutputStreamWriter(fos, "UTF-8");
osw.write("这是一个新文件!");
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (osw != null) {
osw.close();
}
if (fos != null) {
fos.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
TextFileSample sample = new TextFileSample();
sample.isrSample();
sample.oswSample();
}
}
3. 缓冲区及应用
package com.imooc.io;
import java.io.*;
public class TextFileSample {
public void readBuffer(){
Reader reader =null;
BufferedReader br = null;
try{
File file = new File("d:/FileSample.java");
reader = new FileReader(file);
br = new BufferedReader(reader);
String line = null;//行文本
while((line = br.readLine()) != null){
System.out.println(line);
}
}catch (IOException e){
e.printStackTrace();
}finally {
try {
if (br != null) {
br.close();
}
if(reader!= null){
reader.close();
}
}catch (IOException e){
e.printStackTrace();
}
}
}
public static void main(String[] args) {
TextFileSample sample = new TextFileSample();
sample.readBuffer();
}
}
4. 其他流的应用
5. 练习:利用URLConnection对象下载网络图片
package com.imooc.io;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
/**
* 根据图片的url下载到本地
*/
public class URLConnectionSample {
public static void main(String[] args) {
InputStream is = null;
OutputStream os = null;
try {
URL url = new URL("https://img-home.csdnimg.cn/images/20240111100221.jpeg");
//URLConnection对象可根据url获取对应字节
URLConnection connection = url.openConnection();
is = connection.getInputStream();
os = new FileOutputStream("d:/20240111100221.jpeg");
byte[] bs = new byte[1024];
int len = 0;
while((len = is.read(bs)) != -1){
//System.out.println(len);
os.write(bs,0,len);
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if(os != null){
os.close();
}
if (is != null) {
is.close();
}
}catch (IOException e){
e.printStackTrace();
}
}
}
}
6. 总结
