Java中避免NullPointerException的方法总结

// good
"string literal".equals(strObject)
// not good
strObject.equals("string literal")

javaBigDecimal bd = getPrice();
// good
String.valueOf(bd);
// not good
bd.toString();

StringUtils.isEmpty(null); // returns true
StringUtils.isBlank(null); // returns true
StringUtils.isNumeric(null); // returns false
StringUtils.isAllUpperCase(null); // returns false

Collections辅助类中有静态的EMPTY_LIST EMPTY_SET EMPTY_MAP，可以方便的使用它们

public List<Integer> f() {
  try {
    // ...
    return result;
  } catch (SomeException e) {
    e.printStackTrace();
    return Collections.EMPTY_LIST;
  }
}

java@NonNull List<String> strList; // A non-null list of Strings.
List<@NonNull String> strList; // A list of non-null Strings. 

java// Integer getPrice();
int price = obj.getPrice();

javapublic class A {
  private List<Integer> intList = new ArrayList<Integer>();
  private String str = "";
}

JsonNode root = ...;
JsonNode child = root.get("lv1").get("lv2");

JsonNode root = ...;
JsonNode child = root.path("lv1").path("lv2");

if (child.isMissingNode()) { ... }