第16章 字节流与字符流
72 流的基本概念
File类是唯一一个与文件本身有关的程序处理类
File类只能够操作文件本身,而不能操作文件内容
IO操作:输入输出操作
java.io 抽象类
输出 输入
字节流:OutputStream, InputStream
字符流:Writer, Reader
文件处理流程:
1、File找到一个文件
2、通过字节流或字符流的子类为父类对象实例化
3、利用字节流或字符流中的方法实现数据出入与输出操作
4、流的操作属于资源操作,资源操作必须进行关闭
73 OutputStream字节输出流
实现代码
public interface AutoCloseable {
void close() throws Exception;
}
public interface Closeable extends AutoCloseable {
public void close() throws IOException;
}
public interface Flushable {
void flush() throws IOException;
}
public abstract class OutputStream
implements Closeable, Flushable{
public abstract void write(int b) throws IOException;
public void write(byte b[]) throws IOException;
public void write(byte b[], int off, int len) throws IOException;
}
// 子类
public class FileOutputStream extends OutputStream{
// 覆盖
public FileOutputStream(File file) throws FileNotFoundException
// 追加
public FileOutputStream(File file, boolean append)
throws FileNotFoundException;
}
内容输出到文件
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
class Demo{
public static void main(String[] args) throws IOException {
File file = new File("demo/demo.txt");
// 父级目录不存在则创建
if(!file.getParentFile().exists()){
file.getParentFile().mkdir();
}
String message = "这是输出的内容";
// 将字符串转换为字节数组输出到文件,并关闭文件
FileOutputStream output = new FileOutputStream(file);
output.write(message.getBytes());
output.close();
}
}
自动关闭的写法
try(FileOutputStream output = new FileOutputStream(file)){
output.write(message.getBytes());
}catch (IOException e){
e.printStackTrace();
}
使用追加换行输出
String message = "这是输出的内容\r\n";
FileOutputStream output = new FileOutputStream(file, true);
output.write(message.getBytes());
output.close();
74 InputStream字节输入流
public abstract class InputStream implements Closeable{
// 读取单个字节数据,读到文件底部返回-1
public abstract int read() throws IOException;
// 读取一组字节数据,返回读取的个数,文件底部返回-1
public int read(byte b[]) throws IOException;
public int read(byte b[], int off, int len) throws IOException;
}
文件尾部返回 -1, 表示文件读取完成
子类
public class FileInputStream extends InputStream{
public FileInputStream(String name) throws FileNotFoundException
public FileInputStream(File file) throws FileNotFoundException
}
读取示例
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
class Demo{
public static void main(String[] args) throws IOException {
File file = new File("demo/demo.txt");
FileInputStream input = new FileInputStream(file);
// 开辟缓冲区读取数据
byte[] data = new byte[1024];
int len = input.read(data);
System.out.println("[" + new String(data, 0, len) + "]");
input.close();
}
}
75 Writer字符输出流
Writer可以直接输出字符串
public abstract class Writer
implements Appendable, Closeable, Flushable{
public void write(char cbuf[]) throws IOException;
public void write(String str) throws IOException;
}
public class OutputStreamWriter extends Writer
public class FileWriter extends OutputStreamWriter{
public FileWriter(String fileName, boolean append);
public FileWriter(String fileName)
public FileWriter(File file)
public FileWriter(File file, boolean append)
}
代码实例
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
class Demo{
public static void main(String[] args) throws IOException {
File file = new File("demo/demo.txt");
FileWriter writer = new FileWriter(file);
writer.write("hello java");
writer.append("你好!java!");
writer.close();
}
}
76 Reader字符输入流
继承关系
public abstract class Reader implements Readable, Closeable
public class InputStreamReader extends Reader
public class FileReader extends InputStreamReader{
public FileReader(File file);
public FileReader(String fileName);
}
读取示例
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
class Demo{
public static void main(String[] args) throws IOException {
File file = new File("demo/demo.txt");
FileReader reader = new FileReader(file);
char[] data= new char[1024];
int len = reader.read(data);
System.out.println(new String(data, 0, len));
reader.close();
}
}
字符流读取只能按照数组数据读取
77 字节流与字符流的区别
不使用close关闭
使用字节流输出 OutputStream 正常输出
使用字符流输出 Writer 无法输出,使用了缓冲区
close会强制刷新缓冲区(flush)
字节流不使用缓冲区,字符流使用缓冲区
78 转换流
字节流与字符流操作的功能转换
import java.io.*;
class Demo{
public static void main(String[] args) throws IOException {
File file = new File("demo/demo.txt");
// 字节流转字符流操作
OutputStream out = new FileOutputStream(file);
Writer wirter = new OutputStreamWriter(out);
wirter.write("你好");
wirter.close();
}
}
继承关系
OutputStream(Closeable, Flushable)
-FileOutputStream
InputStream(Closeable)
-FileInputStream
Writer(Appendable, Closeable, Flushable)
-OutputStreamWriter
-FileWriter
Reader(Readable, Closeable)
-InputStreamReader
-FileReader
缓存,程序中间缓冲区
字节数据:101010101…
79 综合实战:文件拷贝
实现文件拷贝操作
使用字节流
方案一:
全部读取,一次性输出
方法二:
每次读取一部分,输出一部分
import java.io.*;
class FileUtil {
public static void copyFile(String src, String target) throws IOException {
InputStream input = new FileInputStream(src);
OutputStream output = new FileOutputStream(target);
byte[] data = new byte[1024];
int len = 0;
while ((len = input.read(data)) != -1) {
output.write(data, 0, len);
}
input.close();
output.close();
}
public static void copyDir(String src, String target) throws IOException {
File srcFile = new File(src);
File targetFile = new File(target);
if (!targetFile.exists()) {
targetFile.mkdirs();
}
File[] results = srcFile.listFiles();
if (results != null) {
for (File file : results) {
String fileName = targetFile + File.separator + file.getName();
if (file.isDirectory()) {
copyDir(file.getPath(), fileName);
} else {
copyFile(file.getPath(), fileName);
}
}
}
}
}
class Demo {
public static void main(String[] args) throws IOException {
FileUtil.copyDir("demo", "demo2");
System.out.println("拷贝完成");
}
}
如果拷贝目录则使用递归拷贝