2019独角兽企业重金招聘Python工程师标准>>> 
（3）练习拷贝文件
import s20190517.ReaderTest3;
import java.io.*;
public class CopyDemo {
public static void main(String[] args) {
//创建文件
File file = new File("src\\s20190517\\ReaderTest3.java");
File file1 = new File("ReaderTest3.java");
Reader reader = null;
Writer writer = null;
try {
reader = new FileReader(file);
writer = new FileWriter(file1);
int len = 1;
char[] cs = new char[1024];
while ((len = reader.read(cs)) != -1) {
writer.write(cs, 0, len);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (reader != null) {
reader.close();
}
if (writer != null) {
writer.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
（4）高效输入流
package s20190520;
import java.io.*;
public class BufferedReaderDemo {
public static void main(String[] args) {
//创建一个BufferedReader对象
BufferedReader reader=null;
try {
//注意BufferedReader构造器传入的是Reader对象为参数
reader=new BufferedReader(new FileReader("src\\s20190520\\CopyDemo.java"));
/*//读取一个文本行,边界是null
String s = reader.readLine();
System.out.println(s);*/
//使用循环读取整个文件
String line=null;
while ((line=reader.readLine())!=null){
System.out.println(line);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
//外层关闭的时候内层自动关闭
if(reader!=null){
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
（5）高效输出流
import java.io.*;
public class BufferedWriterDemo {
public static void main(String[] args) {
//创建一个BufferedWriter对象
BufferedWriter writer=null;
try {
writer=new BufferedWriter(new FileWriter("a.txt"));
writer.write("莫名我就喜欢你");
writer.newLine();//换行，要写下一行的时候必须进行这个操作才会换行
writer.flush();//刷新
} catch (Exception e) {
e.printStackTrace();
} finally {
//外层关闭的时候内层自动关闭
if(writer!=null){
try {
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
import java.io.*;
public class BufferCopyDemo {
public static void main(String[] args) {
BufferedReader reader=null;
BufferedWriter writer=null;
try {
reader=new BufferedReader(new FileReader("src\\s20190517\\ReaderTest3.java"));
writer=new BufferedWriter(new FileWriter("ReaderTest3.java"));
//定义一个读取和被写入的字符串
String line=null;
//给字符串赋值，null作为循环终止条件
while ((line=reader.readLine())!=null){
//每次写入一行换行并刷新
writer.write(line);
writer.newLine();
writer.flush();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if(reader!=null){
reader.close();
}
if(writer!=null){
writer.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
83.字节流
import java.io.*;
public class OutputStreamDemo {
public static void main(String[] args) {
//创建一个输出字节流
OutputStream out = null;
try {
byte[] bs={98,99,100,101,102};
//可以new File或者直接写文件名
out = new FileOutputStream(new File("aa.txt"));
//写入单个字符
out.write(98);
//写入整个数组
out.write(bs);
//写入数组的指定部分
out.write(bs,2,2);
} catch (Exception e) {
e.printStackTrace();
} finally {
//关闭资源
if(out!=null){
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
字节流不需要flush
import java.io.*;
public class InputStreamDemo {
public static void main(String[] args) {
InputStream in=null;
try {
in=new FileInputStream(new File("aa.txt"));
//读到的内容也是以assci码显示
int read = in.read();
//转化为字节，读一个字节，如果是汉字或者其他国家文字一次读半个字符可能会出现乱码
System.out.println((char)read);
read = in.read();
System.out.println((char)read);
} catch (Exception e) {
e.printStackTrace();
} finally {
if(in!=null){
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
import java.io.*;
import java.util.Arrays;
public class InputStreamDemo1 {
public static void main(String[] args) {
InputStream in=null;
try {
in=new FileInputStream("aa.txt");
byte[] bs=new byte[6];
int len = in.read(bs);
System.out.println("读取的长度是"+len+" 读取的内容是"+Arrays.toString(bs) +" 转换成字符串打印"+new String(bs));
len = in.read(bs);
System.out.println("读取的长度是"+len+" 读取的内容是"+new String(bs) );
} catch (Exception e) {
e.printStackTrace();
} finally {
if(in!=null){
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
public class InputStreamDemo2 {
public static void main(String[] args) {
InputStream in=null;
try {
in=new FileInputStream("aa.txt");
//定义一个字符串,如果中间有汉字最好长度尽可能长包括
byte[] bs=new byte[3];
//定义读取的长度
int len = 0;
while((len=in.read(bs))!=-1){
System.out.print(new String(bs,0,len));
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if(in!=null){
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
拷贝二进制文件（如压缩包、图片）
import java.io.*;
public class CopyDemo1 {
public static void main(String[] args) {
OutputStream out=null;
InputStream in=null;
try {
//创建字节流输入对象，输入需要读取的对象参数
in=new FileInputStream(new File("C:\\Users\\cheung\\Desktop\\DCIM\\P90122-184132.jpg"));
//创建字节流输出对象
out=new FileOutputStream("P90122-184132.jpg");
//创建数组接收读取的内容
byte[] bs=new byte[1024];
int len=0;
while((len=in.read(bs))!=-1){
//将读取的内容写入输出
out.write(bs,0,len);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if(in!=null){
in.close();
}
if(out!=null){
out.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
84.高效缓冲字节流
import java.io.*;
public class BufferedCopyDemo2 {
public static void main(String[] args) {
BufferedInputStream in=null;
BufferedOutputStream out=null;
try {
in=new BufferedInputStream(new FileInputStream("C:\\Users\\cheung\\Desktop\\DCIM\\Selfie\\P80812-152904.jpg"));
out=new BufferedOutputStream(new FileOutputStream("P80812-152904.jpg"));
byte[] bs=new byte[1024];
//定义一个读取长度标识
int len=0;
while((len=in.read(bs))!=-1){
out.write(bs);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if(in!=null){
in.close();
}
if(out!=null){
out.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}