BufferedinputStream学习

清疚 2022-09-04 05:49 154阅读 0赞

## 思考：有了inputStream为什么还需要BufferedInputStream？ ##

**inputStream**和**bufferedInputStream**的区别就是后者带有缓冲区，前者没有

inoutStream在读取的时候，每读一个字节就需要写入一个字节，这样就会频繁的进行IO操作

bufferedInputStream带缓冲区的流，可以一次性读取很多字节，但是不往磁盘中写入，只是放在内存中，等凑够了缓冲区大小的是时候，一次性写入到磁盘中

也就引生出了一个需要注意的地方

> 在使用bufferedInputStream读写完数据之后，记得需要使用flush()方法或者close()方法，强制的将缓冲区中的数据写出  
> flush和close的区别  
> close 在close时候，会自动进行flush  
> 在不调用close，并且缓冲区未满的情况下，又需要把缓冲区的内容写入到文件，这时候用flush

写代码进行对比两个时间消耗

package com.picc.eloan.assit.ned.utils;
    
    import java.io.*;
    import java.util.zip.CRC32;
    import java.util.zip.CheckedInputStream;
    import java.util.zip.ZipEntry;
    import java.util.zip.ZipOutputStream;
    
    
    /** * @author luodong * @date 2021/8/11 */
    public class ZipResult { 
        //主函数
        public static void main(String[] args) { 
    
            copyFile();
    
            copyFileInputStream();
        }
    
        public static void copyFile() { 
            long startTime = System.currentTimeMillis();
            String filePath="/Users/luodong/Documents/photo/algorithm-base-main.zip";
            String copyPath = "/Users/luodong/Documents/test/algorithm-base-main.zip";
            FileInputStream inputStream = null;
            BufferedInputStream bufferedInputStream = null;
            FileOutputStream outputStream = null;
            BufferedOutputStream bufferedOutputStream = null;
            try { 
                inputStream = new FileInputStream(filePath);
                bufferedInputStream = new BufferedInputStream(inputStream);
                outputStream = new FileOutputStream(copyPath);
                bufferedOutputStream = new BufferedOutputStream(outputStream);
    
              byte[] b =  new byte[1024];
              int length = 0;
                while((length=bufferedInputStream.read(b))!=-1){ 
                  bufferedOutputStream.write(b, 0, length );
              }
              bufferedOutputStream.flush();
                long endTime = System.currentTimeMillis();
                System.out.println(endTime-startTime+"耗时");
            } catch (FileNotFoundException e) { 
                e.printStackTrace();
            } catch (IOException e) { 
                e.printStackTrace();
            }finally { 
                if( bufferedOutputStream != null ){ 
                    try { 
                        bufferedOutputStream.close();
                    } catch (IOException e) { 
                        e.printStackTrace();
                    }
                }
    
                if( bufferedInputStream != null){ 
                    try { 
                        bufferedInputStream.close();
                    } catch (IOException e) { 
                        e.printStackTrace();
                    }
                }
    
                if( inputStream != null ){ 
                    try { 
                        inputStream.close();
                    } catch (IOException e) { 
                        e.printStackTrace();
                    }
                }
    
                if ( outputStream != null ) { 
                    try { 
                        outputStream.close();
                    } catch (IOException e) { 
                        e.printStackTrace();
                    }
                }
            }
    
        }
    
    
        public static void copyFileInputStream() { 
            long startTime = System.currentTimeMillis();
            String filePath="/Users/luodong/Documents/photo/algorithm-base-main.zip";
            String copyPath = "/Users/luodong/Documents/test/algorithm-base-main.zip";
            FileInputStream inputStream = null;
    
            FileOutputStream outputStream = null;
    
            try { 
                inputStream = new FileInputStream(filePath);
                outputStream = new FileOutputStream(copyPath);
    
                byte[] b =  new byte[1024];
                int length = 0;
                while((length=inputStream.read(b))!=-1){ 
                   outputStream.write(b, 0, length );
                }
                outputStream.flush();
                long endTime = System.currentTimeMillis();
                System.out.println(endTime-startTime+"耗时");
            } catch (FileNotFoundException e) { 
                e.printStackTrace();
            } catch (IOException e) { 
                e.printStackTrace();
            }finally { 
                if( inputStream != null ){ 
                    try { 
                        inputStream.close();
                    } catch (IOException e) { 
                        e.printStackTrace();
                    }
                }
    
                if ( outputStream != null ) { 
                    try { 
                        outputStream.close();
                    } catch (IOException e) { 
                        e.printStackTrace();
                    }
                }
            }
    
        }
    
    }

运行结果

com.picc.eloan.assit.ned.utils.ZipResult
    1耗时
    2耗时
    
    Process finished with exit code 0