为什么我的字符串不接受null？

Question

I need the String if it is not found in mapper.getChave is what is returned. What I do? If I only get nullPointerException

for(String chave : linha.keySet()) {
                //Processa chave
                String novaChave = mapper.getChave(chave.trim());
                if (!(novaChave == null || novaChave.isEmpty())) {
                    //Processa valor
                    String novoValor = linha.getString(chave);
                    temp.append(novaChave, novoValor);
                }
                else {
                    extras.append(chave, linha.getString(chave));
                }

            }

Log

java.lang.NullPointerException
    at oknok.validacao.readers.PlanilhaReader.processaAtributosPlanilha(PlanilhaReader.java:237)

Line 237 is

String novaChave = mapper.getChave(chave.trim());

: The first time the loop runs, i have a Nullpointer and chave contains a value

System.out.println(chave.isEmpty() + "\t" + chave + "\t" + chave.trim());

Output

false   Veículo Veículo

Answer 1

You need to add null check for mapper as well as chave .

if (mapper!= null && chave != null && !"".equals(chave) {
    // do something
}

---

mapper.getChave(chave.trim())
       ^              ^   possible places for NPE.

Answer 2

chave或mapper值很可能为null，并且您分别在它们上调用trim()和.getChave()导致nullpointer

Answer 3

You need to check whether chave is null before trimming it or doing anything else (I'm assuming that mapper is pre-initialised and not null, but you should check that too)

eg

if (chave != null && !"".equals(chave.trim()) {
   // now do something
}

You may find it easier (more intuitive) to use something like Apache Commons StringUtils.isNotBlank(String) . See here for the doc.

Answer 4

linha.keySet()有一个空字符串引用。

Answer 5

按照代码将空字符串更改为“”：您可以将“”更改为任意内容

String novaChave = mapper.getChave((chave == null ? "" : chave).trim());