Java访问系统保护文件报错NullPointerException怎么办

Question

写个自动备份文件的程序，网上抄了个方法并小改了下：

public static boolean copyFileUsingFileChannels(File source, File dest) throws IOException {
    boolean scu;
    FileChannel inputChannel = null;
    FileChannel outputChannel = null;
    try {
        inputChannel = new FileInputStream(source).getChannel();
        outputChannel = new FileOutputStream(dest).getChannel();
        outputChannel.transferFrom(inputChannel, 0, inputChannel.size());
        scu = true;
    } catch (Exception e) {
        scu = false;
    }finally {
        inputChannel.close();  //报错里的54行
        outputChannel.close();
    }
    return scu;
}

复制方法：

static int fail = 0;
static int error = 0;

public static void fileCopy(File file1, File file2) throws IOException {
    File[] files1 = file1.listFiles();
    if(files1 == null) {    //如果是系统保护文件夹，files1为null
        error ++;            //计数：出错
        return;
    }
    for (int i = 0; i < files1.length; i++) {
        
        if (files1[i].isDirectory()) {
            String s = files1[i].getName();
            File file = new File(file2.getPath() + "/" + s);
            file.mkdir();
            fileCopy(files1[i], file);        //递归
        } else if (files1[i].isFile()) {
            System.out.println(files1[i].getPath());  //输出当前文件路径
            String str = files1[i].getPath().substring(
                    file1.getPath().length(), 
                    files1[i].getPath().length());
            //GFile为粘贴路径
            File GFile = new File(file2.getPath() + "\\" + str);
            /**
            *    省略部分：检测是否为相同文件，相同则continue;
            */
            if(!Test.copyFileUsingFileChannels(files1[i], GFile))  //报错里的74行
                fail++;        //计数：复制失败
        }
    }
}

现在对于系统保护文件夹能直接跳过，但单个文件比如pagefile.sys不知道怎么跳过，还是会报错

h:\pagefile.sys
Exception in thread "main" java.lang.NullPointerException
    at bag.Test.copyFileUsingFileChannels(Test.java:54)
    at bag.CopyFiles.fileCopy(CopyFiles.java:74)
    at bag.CopyFiles.main(CopyFiles.java:89)

Answer 1

就是你报错的那一行的inputChannel是null导致的空指针异常，把那一行改成：

if(inputChannel != null){
  inputChannel.close();
}