用MappedByteBuffer进行特大文件拷贝分割

目的：
    有时候用U盘转移大文件时，U盘空间太小，想写一个小程序能把文件分割方便转移。

问题一：用Buffer直接将文件（1G以上）映入内存，不可能直接进物理内存。
    解决方案：将文件用Map映射到一个MappedByteBuffer中

问题二：报告“java.io.IOException: 存储空间不足，无法处理此命令。”异常。
    解决方案：将文件分段映射。注意文件较大时必须显式调用
              System.gc();
            System.runFinalization();
            否则还是可能报上述异常。
        原因：《JAVA编程思想》4.3 清除：收尾和垃圾收集  有如下说明：
              当然，Java可用垃圾收集器回收由不再使用的对象占据的内存。现在考虑
              一种非常特殊且不多见的情况。假定我们的对象分配了一个“特殊”内存区
              域，没有使用new。垃圾收集器只知道释放那些由new分配的内存，所以不知
              道如何释放对象的“特殊”内存。为解决这个问题，Java提供了一个名为
              finalize()的方法，可为我们的类定义它。

问题三：原文件不可被删除（在程序退出之前）。
    解决方案：JDK API 1.60中有“映射的字节缓冲区和它所表示的文件映射关系在该缓冲
              区本身成为垃圾回收缓冲区之前一直保持有效。 ”关于此问题众说纷纭，并
              且在sun.bug中也在讨论。笔者认为只要最后把映射指向一个无关的文件即可
              解决。

关键代码：
              frame.jTextField6.getText()  //待分割的文件
              frame.jTextField5.getText()+" \\"+this.findname() //保存位置
              findex   //方便以后组合

 

try{    
                        File fcut = new File(frame.jTextField6.getText());    
                        File fsave = new File(frame.jTextField5.getText()+"\\"+ this.findname());    
                         if(!fsave.exists()){    
                                fsave.mkdir();    
                        }    
                        File findex = new File(frame.jTextField5.getText()+ "\\"+this.findname()+"\\cut.index");    
                        FileWriter fw = new FileWriter(findex);    
                        BufferedWriter bw = new BufferedWriter(fw);    
                        bw.write( this.findname()+ "."+ this.findkuozhan(),0,( this.findname()+ "."+ this.findkuozhan()).length());    
                        bw.newLine();    
    
                         int num = size_i;     //分割份数    
                         long totalsize = fcut.length();     //文件总大小    
                         long persize = totalsize/num;         //每个大小    
    
                        FileInputStream fis = new FileInputStream(fcut);    
                        FileChannel fic = fis.getChannel();    
    
                         if(persize>buffersize){    
                                 for( int i=0;i<num;i++){    
                                        RandomAccessFile ras = new RandomAccessFile(frame.jTextField5.getText()+ "\\"+this.findname()+"\\"+ this.findname()+ ".cut"+(i+1), "rw");    
                                        FileChannel frs = ras.getChannel();    
                                         if(i<num-1){    
                                                 for ( int j = 0; j < persize / buffersize; j++) {    
                                                         if (j < persize / buffersize - 1) {    
                                                                MappedByteBuffer mibb = fic.map(FileChannel.MapMode.READ_ONLY,i * persize + j * buffersize,buffersize);    
                                                                MappedByteBuffer mobb = frs.map(FileChannel.MapMode.READ_WRITE,j*buffersize,buffersize);    
                                                                mobb.put(mibb);    
                                                                mibb.clear();    
                                                                mobb.clear();    
                                                        } else{    
                                                                MappedByteBuffer mibb = fic.map(FileChannel.MapMode.READ_ONLY,i * persize + j * buffersize,buffersize+persize%buffersize);    
                                                                MappedByteBuffer mobb = frs.map(FileChannel.MapMode.READ_WRITE,j*buffersize,buffersize+persize%buffersize);    
                                                                mobb.put(mibb);    
                                                                mibb.clear();    
                                                                mobb.clear();    
                                                        }    
                                                }    
                                                System.gc();    
                                                System.runFinalization();    
                                                bw.write(frame.jTextField5.getText()+ "\\"+this.findname()+"\\"+ this.findname()+ ".cut"+(i+1),0,(frame.jTextField5.getText()+ "\\"+this.findname()+"\\"+ this.findname()+ ".cut"+(i+1)).length());    
                                                bw.newLine();    
                                        } else{    
                                                 for ( int j = 0; j < persize / buffersize; j++) {    
                                                         if (j < persize / buffersize - 1) {    
                                                                MappedByteBuffer mibb = fic.map(FileChannel.MapMode.READ_ONLY,i * persize + j * buffersize,buffersize);    
                                                                MappedByteBuffer mobb = frs.map(FileChannel.MapMode.READ_WRITE,j*buffersize,buffersize);    
                                                                mobb.put(mibb);    
                                                                mibb.clear();    
                                                                mobb.clear();    
                                                        } else{    
                                                                MappedByteBuffer mibb = fic.map(FileChannel.MapMode.READ_ONLY,i * persize + j * buffersize,totalsize-(i * persize + j * buffersize));    
                                                                MappedByteBuffer mobb = frs.map(FileChannel.MapMode.READ_WRITE,j*buffersize,totalsize-(i * persize + j * buffersize));    
                                                                mobb.put(mibb);    
                                                                mibb.clear();    
                                                                mobb.clear();    
                                                        }    
                                                }    
                                                System.gc();    
                                                System.runFinalization();    
                                                bw.write(frame.jTextField5.getText()+ "\\"+this.findname()+"\\"+ this.findname()+ ".cut"+(i+1),0,(frame.jTextField5.getText()+ "\\"+this.findname()+"\\"+ this.findname()+ ".cut"+(i+1)).length());    
                                                bw.close();    
                                                fw.close();    
                                        }    
                                        ras.close();    
                                        frs.close();    
                                }    
                                fis.close();    
                                fic.close();    
    
                        } else{    
                                 for( int i=0;i<num;i++){    
                                        RandomAccessFile ras = new RandomAccessFile(frame.jTextField5.getText()+ "\\"+this.findname()+"\\"+ this.findname()+ ".cut"+(i+1), "rw");    
                                        FileChannel frs = ras.getChannel();    
                                         if(i<num-1){    
    
                                                MappedByteBuffer mibb = fic.map(FileChannel.MapMode.READ_ONLY,i * persize,persize);    
                                                MappedByteBuffer mobb = frs.map(FileChannel.MapMode.READ_WRITE,0,persize);    
                                                mobb.put(mibb);    
                                                mibb.clear();    
                                                mobb.clear();    
    
                                                System.gc();    
                                                System.runFinalization();    
                                                bw.write(frame.jTextField5.getText()+ "\\"+this.findname()+"\\"+ this.findname()+ ".cut"+(i+1),0,(frame.jTextField5.getText()+ "\\"+this.findname()+"\\"+ this.findname()+ ".cut"+(i+1)).length());    
                                                bw.newLine();    
                                        } else{    
    
                                                MappedByteBuffer mibb = fic.map(FileChannel.MapMode.READ_ONLY,i * persize,totalsize-i * persize);    
                                                MappedByteBuffer mobb = frs.map(FileChannel.MapMode.READ_WRITE,0,totalsize-i * persize);    
                                                mobb.put(mibb);    
                                                mibb.clear();    
                                                mobb.clear();    
    
                                                System.gc();    
                                                System.runFinalization();    
                                                bw.write(frame.jTextField5.getText()+ "\\"+this.findname()+"\\"+ this.findname()+ ".cut"+(i+1),0,(frame.jTextField5.getText()+ "\\"+this.findname()+"\\"+ this.findname()+ ".cut"+(i+1)).length());    
                                                bw.close();    
                                                fw.close();    
                                        }    
                                        ras.close();    
                                        frs.close();    
                                }    
                                fis.close();    
                                fic.close();    
    
    
                        }    
                jop = new JOptionPane();    
                jop.showMessageDialog(frame.getContentPane(), "文件分割完毕！", "成功", JOptionPane.ERROR_MESSAGE);    
                } catch(Exception e){    
                        jop = new JOptionPane();    
                        jop.showMessageDialog(frame.getContentPane(),e.toString(), "错误", JOptionPane.ERROR_MESSAGE);    
                }