黑马程序员——Java IO总结(二)

黑马程序员——Java IO总结(二)

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一、字符流的缓冲区
l 缓冲区的出现提高了对数据的读写效率
l 对应类
BufferedWriter
BufferedReader
l 缓冲区要结合流才可以使用。
l 在流的基础上对流的功能进行了增强。

l 实例：字符写入流缓冲区实例

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

public class BufferedWriterDemo {
public static void main(String[] args) throws IOException {
FileWriter writer = new FileWriter("buffer.txt");

// 为了提高字符写入效率，加入了缓冲技术
BufferedWriter br = new BufferedWriter(writer);

br.write("中国");
br.newLine(); // 插入跨平台的换行符
br.write("Java技术");

// 只要用到缓冲区，就要记得刷新
br.flush();

// 其实关闭缓冲区，就是关闭缓冲区中的流对象
br.close();
}
}

l 实例：字符读取流缓冲区实例

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class BufferedReaderDemo {
public static void main(String[] args) throws IOException {
FileReader reader = new FileReader("buffer.txt");

BufferedReader br = new BufferedReader(reader);

String line = null;

while ((line = br.readLine()) != null) {
System.out.println(line);
}

br.close();
}
}

l 实例：通过缓冲区复制文本文件

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class TextFileCopyBuf {
public static void main(String[] args) {
BufferedReader br = null;
BufferedWriter bw = null;

try {
br = new BufferedReader(new FileReader("buffer.txt"));
bw = new BufferedWriter(new FileWriter("d:\\buffer.txt"));

String line = null;

while ((line = br.readLine()) != null) {
bw.write(line);
bw.newLine();
bw.flush();
}
} catch (Exception e) {
throw new RuntimeException("文件读写失败！");
} finally {
try {
if (br != null)
br.close();
} catch (IOException e) {
throw new RuntimeException("读取关闭失败!");
}
try {
if (bw != null)
bw.close();
} catch (IOException e) {
throw new RuntimeException("写入关闭失败！");
}
}
}
}

l 装饰设计模式
当想要对已有的对象进行增强时，可以定义类，将已有对象传入，基于已有的功能，并提供加强功能，那么自定义的类称为装饰类。
l 实例：模拟一个带行号的缓冲区对象

import java.io.FileReader;
import java.io.IOException;
import java.io.Reader;

public class MyLineNumberReader {
private Reader r;
private int lineNumber;

public MyLineNumberReader(Reader r) {
super();
this.r = r;
}

public int getLineNumber() {
return lineNumber;
}

public void setLineNumber(int lineNumber) {
this.lineNumber = lineNumber;
}

public String readLine() throws IOException {
StringBuilder sb = new StringBuilder();

lineNumber++;
int ch = 0;

while ((ch = r.read()) != -1) {
if (ch == '\r')
continue;
else if (ch == '\n')
return sb.toString();
else
sb.append((char) ch);
}

if (sb.length() > 0)
return sb.toString();

return null;
}

public void close() throws IOException {
r.close();
}

public static void main(String[] args) throws IOException {
FileReader r = new FileReader("FileReaderDemo_copy.java");
MyLineNumberReader lnr = new MyLineNumberReader(r);

String line = null;

lnr.setLineNumber(100);
while ((line = lnr.readLine()) != null) {
System.out.println(lnr.getLineNumber() + ": " + line);
}

lnr.close();
}
}

二、字节流操作
l 字节流基类：InputStream、OutputStream
l 实例：字节流的读写

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileOutputStreamDemo {
public static void main(String[] args) throws IOException {
// writeFile();
readFile3();
}

public static void readFile1() throws IOException {
FileInputStream fis = new FileInputStream("fos.txt");

int ch = 0;

while ((ch = fis.read()) != -1) {
System.out.print((char) ch);
}

fis.close();
}

public static void readFile2() throws IOException {
FileInputStream fis = new FileInputStream("fos.txt");

int len = 0;
byte[] buf = new byte[1024];

while ((len = fis.read(buf)) != -1) {
System.out.println(new String(buf, 0, len));
}

fis.close();
}

public static void readFile3() throws IOException {
FileInputStream fis = new FileInputStream("fos.txt");

byte[] buf=new byte[fis.available()];

fis.read(buf);
System.out.println(new String(buf));

fis.close();
}

public static void writeFile() throws IOException {
FileOutputStream fos = new FileOutputStream("fos.txt");

fos.write("HelloWorld".getBytes());

fos.close();
}
}

l 实例：复制图片

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

// 复制图片
public class CopyPic {
public static void main(String[] args) {
FileOutputStream fos = null;
FileInputStream fis = null;

try {
fis = new FileInputStream("c:\\a.jpg");
fos = new FileOutputStream("c:\\b.jpg");

byte[] buf = new byte[1024];
int len = 0;

while ((len = fis.read(buf)) != -1) {
fos.write(buf, 0, len);
}

} catch (Exception e) {
throw new RuntimeException(e);
} finally {
try {
if (fis != null)
fis.close();
} catch (IOException e) {
e.printStackTrace();
}
try {
if (fos != null)
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

l 实例：通过缓冲区复制mp3文件

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class CopyMp3 {
public static void main(String[] args) throws IOException {
long start = System.currentTimeMillis();
copy_1();
long end = System.currentTimeMillis();

System.out.println(end - start);
}

// 通过字节流的缓冲区完成复制
public static void copy_1() throws IOException {
BufferedInputStream bufis = new BufferedInputStream(
new FileInputStream("d:/1.mp3"));
BufferedOutputStream bufos = new BufferedOutputStream(
new FileOutputStream("d:/1_copy.mp3"));

int b = 0;

while ((b = bufis.read()) != -1) {
bufos.write(b);
}

bufis.close();
bufos.close();
}
}

l 实例：读取键盘录入

import java.io.IOException;
import java.io.InputStream;

public class ReadIn {
public static void main(String[] args) throws IOException {
InputStream in = System.in;
StringBuilder sb = new StringBuilder();

while (true) {
int ch = in.read();
if (ch == '\r')
continue;
else if (ch == '\n') {
String s = sb.toString();
sb.delete(0, sb.length());
if ("over".equals(s))
break;
System.out.println(s);
continue;
}
sb.append((char) ch);
}
}
}

l 实例：读取键盘录入（使用转换流InputStreamReader）

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

public class ReadIn {
public static void main(String[] args) throws IOException {
InputStream in = System.in;

BufferedReader br = new BufferedReader(new InputStreamReader(in));

String line = null;

while ((line = br.readLine()) != null) {
if ("over".equals(line)) {
break;
}
System.out.println(line);
}
}
}

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----------------------

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