java - java写文件时出现空指针异常

Question

我在写入文件时遇到异常。我给出下面的代码。

private static void readCsvFromFileAmazon(List<String> filelist) 
        throws BiffException, IOException,NullPointerException {

    FileWriter fw = new FileWriter("total_number_of_products_amazon.txt", true);
    String numberOfProducts = getProductNumber(url);

    System.out.println(category);
    System.out.println("@@@@@@@@@@@@@@" + numberOfProducts);
    // call function to get the number of products. \
    if (!numberOfProducts.equals(null) || !numberOfProducts.equals(" "))
    {
        fw.write(numberOfProducts);
    }
    else
    {
        System.out.println("cant write null product");
    }
    fw.close();
}

获取产品数量的值为空则发生异常

Exception in thread "main" 
@@@@@@@@@@@@@@null
java.lang.NullPointerException

该行发生异常

if(!numberOfProducts.equals(null)||!numberOfProducts.equals(" "))

Answer 1

您必须以不同的方式检查 numberOfProducts 内容:

if(null != numberOfProducts ||!"".equals(numberOfProducts))

而不是 if(!numberOfProducts.equals(null)||!numberOfProducts.equals(""))

因为如果 numberOfProducts 为 null，则在 null 对象上调用方法 equals 会抛出 nullPointerException。

希望这有帮助，