Java文件读写操作

Posted 2020-06-18 爱上胡萝卜的猴子

一.获得控制台用户输入的信息

     public String getInputMessage() throws IOException...{
         System.out.println("请输入您的命令∶");
         byte buffer[]=new byte[1024];
         int count=System.in.read(buffer);
         char[] ch=new char[count-2];//最后两位为结束符，删去不要
         for(int i=0;i<count-2;i++)
             ch[i]=(char)buffer[i];
         String str=new String(ch);
         return str;
     }
     可以返回用户输入的信息，不足之处在于不支持中文输入，有待进一步改进。

     二.复制文件
     1.以文件流的方式复制文件

     public void copyFile(String src,String dest) throws IOException...{
         FileInputStream in=new FileInputStream(src);
         File file=new File(dest);
         if(!file.exists())
             file.createNewFile();
         FileOutputStream out=new FileOutputStream(file);
         int c;
         byte buffer[]=new byte[1024];
         while((c=in.read(buffer))!=-1)...{
             for(int i=0;i<c;i++)
                 out.write(buffer[i]);        
         }
         in.close();
         out.close();
     }
     该方法经过测试，支持中文处理，并且可以复制多种类型，比如txt，xml，jpg，doc等多种格式

     三.写文件

     1.利用PrintStream写文件

     public void PrintStreamDemo()...{
         try ...{
             FileOutputStream out=new FileOutputStream("D:/test.txt");
             PrintStream p=new PrintStream(out);
             for(int i=0;i<10;i++)
                 p.println("This is "+i+" line");
         } catch (FileNotFoundException e) ...{
             e.printStackTrace();
         }
     }
     2.利用StringBuffer写文件
public void StringBufferDemo() throws IOException......{
         File file=new File("/root/sms.log");
         if(!file.exists())
             file.createNewFile();
         FileOutputStream out=new FileOutputStream(file,true);        
         for(int i=0;i<10000;i++)......{
             StringBuffer sb=new StringBuffer();
             sb.append("这是第"+i+"行:前面介绍的各种方法都不关用,为什么总是奇怪的问题 ");
             out.write(sb.toString().getBytes("utf-8"));
         }        
         out.close();
     }
     该方法可以设定使用何种编码，有效解决中文问题。
四.文件重命名
    
     public void renameFile(String path,String oldname,String newname)...{
         if(!oldname.equals(newname))...{//新的文件名和以前文件名不同时,才有必要进行重命名
             File oldfile=new File(path+"/"+oldname);
             File newfile=new File(path+"/"+newname);
             if(newfile.exists())//若在该目录下已经有一个文件和新文件名相同，则不允许重命名
                 System.out.println(newname+"已经存在！");
             else...{
                 oldfile.renameTo(newfile);
             }
         }         
     }

  五.转移文件目录
     转移文件目录不等同于复制文件，复制文件是复制后两个目录都存在该文件，而转移文件目录则是转移后，只有新目录中存在该文件。
    
     public void changeDirectory(String filename,String oldpath,String newpath,boolean cover)...{
         if(!oldpath.equals(newpath))...{
             File oldfile=new File(oldpath+"/"+filename);
             File newfile=new File(newpath+"/"+filename);
             if(newfile.exists())...{//若在待转移目录下，已经存在待转移文件
                 if(cover)//覆盖
                     oldfile.renameTo(newfile);
                 else
                     System.out.println("在新目录下已经存在："+filename);
             }
             else...{
                 oldfile.renameTo(newfile);
             }
         }       
     }
     六.读文件
     1.利用FileInputStream读取文件
    
     public String FileInputStreamDemo(String path) throws IOException...{
         File file=new File(path);
         if(!file.exists()||file.isDirectory())
             throw new FileNotFoundException();
         FileInputStream fis=new FileInputStream(file);
         byte[] buf = new byte[1024];
         StringBuffer sb=new StringBuffer();
         while((fis.read(buf))!=-1)...{
             sb.append(new String(buf));    
             buf=new byte[1024];//重新生成，避免和上次读取的数据重复
         }
         return sb.toString();
     }
2.利用BufferedReader读取

     在IO操作，利用BufferedReader和BufferedWriter效率会更高一点

    
     public String BufferedReaderDemo(String path) throws IOException...{
         File file=new File(path);
         if(!file.exists()||file.isDirectory())
             throw new FileNotFoundException();
         BufferedReader br=new BufferedReader(new FileReader(file));
         String temp=null;
         StringBuffer sb=new StringBuffer();
         temp=br.readLine();
         while(temp!=null)...{
             sb.append(temp+" ");
             temp=br.readLine();
         }
         return sb.toString();
     }

     3.利用dom4j读取xml文件

    
     public Document readXml(String path) throws DocumentException, IOException...{
         File file=new File(path);
         BufferedReader bufferedreader = new BufferedReader(new FileReader(file));
         SAXReader saxreader = new SAXReader();
         Document document = (Document)saxreader.read(bufferedreader);
         bufferedreader.close();
         return document;
     }
     七.创建文件(文件夹)

1.创建文件夹  
     public void createDir(String path)...{
         File dir=new File(path);
         if(!dir.exists())
             dir.mkdir();
     }
2.创建新文件
     public void createFile(String path,String filename) throws IOException...{
         File file=new File(path+"/"+filename);
         if(!file.exists())
             file.createNewFile();
     }
     八.删除文件(目录)
1.删除文件     
     public void delFile(String path,String filename)...{
         File file=new File(path+"/"+filename);
         if(file.exists()&&file.isFile())
             file.delete();
     }
2.删除目录
要利用File类的delete()方法删除目录时，必须保证该目录下没有文件或者子目录，否则删除失败，因此在实际应用中，我们要删除目录，必须利用递归删除该目录下的所有子目录和文件，然后再删除该目录。  
     public void delDir(String path)...{
         File dir=new File(path);
         if(dir.exists())...{
             File[] tmp=dir.listFiles();
             for(int i=0;i<tmp.length;i++)...{
                 if(tmp[i].isDirectory())...{
                     delDir(path+"/"+tmp[i].getName());
                 }
                 else...{
                     tmp[i].delete();
                 }
             }
             dir.delete();
         }
     }