Java 8可选替换return null [英] java 8 optional to replace return null

问题描述

我正在将代码重构为Java 8，并且我想用Optional替换空检查.

I am refactoring the code to Java 8 and I want to replace null checks with Optional.

public Employee findEmployeeById(String id) {
    List<Employee> empList = .. //some db query
    return (empList.isEmpty() ? null : empList.get(0));
}

Optional.ofNullable(empList.get(0))将不起作用，因为它会抛出IndexOutofBoundException

Optional.ofNullable(empList.get(0)) won't work as when it will throw IndexOutofBoundException

或者我是否应该将Optional.empty()替换为null?

Or should I ideally replace null with Optional.empty()?

推荐答案

正如@Jesper在评论中已经提到的那样，您必须检查列表是否为空，然后返回空的Optional.

As @Jesper already mentioned in the comments, you have to check whether the list is empty and then return an empty Optional.

public Optional<Employee> findEmployeeById(String id) {
    List<Employee> empList = .. //some db query
    return empList.isEmpty() ? Optional.empty() : Optional.of(empList.get(0));
}

Optional是可能的null值的包装，使用它可以避免在使用null时显式检查null.

An Optional is a wrapper around a potentially null value that allows you to avoid explicitly checking for null when you use it.

查看可选文档查看其提供的功能.

Have a look at the Optional documentation to see what functionality it provides.

例如，您可以获取雇员的姓名或姓名(如果没有)，而无需检查null:

For example you can get an employee's name or "unknown" if it's absent, without checking for null:

Optional<Employee> emp = findEmployeeById(id);
String name = emp.map(Employee::getName).orElse("unknown");

您可以阅读关于Uses for Optional 的信息，以了解是否适合您使用Optional.

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