IO缓冲流—— BufferedInputStream、BufferedOutputStream

港控/mmm° 2021-09-23 01:26 426阅读 0赞

# 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。  
![在这里插入图片描述][20190324160505978.png]

##### 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();
    
        }
    }

![在这里插入图片描述][20190324155959281.png]  
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();
    
        }
    }

![在这里插入图片描述][20190324160546192.png]  
**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  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzg0MzUx_size_16_color_FFFFFF_t_70]

[20190324160505978.png]: /images/20210923/ec09adbbaf9541b689aa95d395c466d8.png
[20190324155959281.png]: /images/20210923/068a5f7d725e488bab820af00e28aa06.png
[20190324160546192.png]: /images/20210923/0526cfdb850140768904ccdf92180560.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxMzg0MzUx_size_16_color_FFFFFF_t_70]: /images/20210923/5e70ab8596194533ad430e6a0d8c5c93.png