一、介绍缓冲流BufferedInputStream、BufferedOutputStream

在创建 BufferedInputStream 时，会创建一个8K的内部缓冲区数组byte[] buf,存储数据的内部缓冲区数组。必要时可用另一个不同大小的数组替换它。

两个构造方法：

• BufferedInputStream(InputStream in) 创建一个 BufferedInputStream 并保存其参数，即输入流 in，以便将来使用。

• BufferedInputStream(InputStream in, int size) 创建具有指定缓冲区大小的 BufferedInputStream 并保存其参数，即输入流 in，以便将来使用。创建一个长度为 size 的内部缓冲区数组并将其存储在 buf 中。

使用示例：

public class BufferedOutputStream {
//缓冲流读操作
public static void read() throws IOException {
String path = "C:\\Users\\50579\\Desktop\\tt.txt";
//文件操作流(操作字节)
FileInputStream fileInputStream = new FileInputStream(path);

//转换流：将字节转换为字符
InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream);

//缓冲流↓↓
//字符缓冲流
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);//构造函数1：默认大小的缓冲区
//BufferedReader bufferedReader1 = new BufferedReader(inputStreamReader, 1);//构造函数2：可以自定义大小的缓冲区

//字节缓冲流
//BufferedInputStream bufferedInputStream = new BufferedInputStream(fileInputStream);

//特有方法：可以一行一行的读取
int line;
while ((line = bufferedReader.read())!= -1){
System.out.println(line);
}
bufferedReader.close();
}

//缓冲流写操作
public static void write() throws IOException {
String path = "C:\\Users\\50579\\Desktop\\tt.txt";

BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(path)));

Random random = new Random();
for (int i = 0; i < 100; i++) {
int i1 = random.nextInt(5) + 5;
StringBuffer stringBuffer = new StringBuffer();
for (int j = 0; j < i1; j++) {
int i2 = random.nextInt(1000) + 1;
stringBuffer.append(i2);
stringBuffer.append(",");
}
writer.write(stringBuffer.toString());
writer.newLine();
}

writer.close();

}
public static void main(String[] args) throws IOException {

write();
read();
}
}

二、给定一个较大的文件，判断InputStream和BufferedInputStream的读取时间大小？

1. BufferedInputStream的读取时间

public class Judge {

public static void main(String[] args) throws IOException {

String path = "E:\\javaSource\\src-insight2\\mysrc.si4project.si4project\\mysrc.si4project.sip_xsb";
FileInputStream fileInputStream = new FileInputStream(path);

//转换流：将字节转换为字符
InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream);

//字符缓冲流
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);

long startTime=System.currentTimeMillis();
System.out.println("开始读");

int line;
while ((line = bufferedReader.read())!= -1){
System.out.println(line);
}

long endTime=System.currentTimeMillis();
System.out.println("BufferedReader读取时间： "+(endTime - startTime)+"ms");

bufferedReader.close();

}
}

2. InputStream的读取时间

public class Judge {

public static void main(String[] args) throws IOException {

String path = "E:\\javaSource\\src-insight2\\mysrc.si4project.si4project\\mysrc.si4project.sip_xsb";

FileInputStream fileInputStream = new FileInputStream(path);

long startTime=System.currentTimeMillis();
System.out.println("开始读");

int line;
while ((line = fileInputStream.read())!= -1){
System.out.println(line);
}

long endTime=System.currentTimeMillis();
System.out.println("BufferedReader读取时间： "+(endTime - startTime)+"ms");

fileInputStream.close();

}
}

总结出：
BufferedInputStream耗时短，效率高，因为它在用户区有个8k（8192）的缓存区，会批量从内核的缓冲区一次拿8K, read每次从用户区的缓存区读取数据，所以比较高效