遇到的问题之“对象不为空，字段为空，取出使用时报空指针异常【特例场景：Optional的使用】”

一、场景

 

二、原因

目前找到的原因是：使用Optional.of()方法对其判空后直接报错了，就没有走orElse了

Optional.of()源码

Optional.java

　　/**
     * Returns an {@code Optional} with the specified present non-null value.
     *
     * @param <T> the class of the value
     * @param value the value to be present, which must be non-null
     * @return an {@code Optional} with the value present
     * @throws NullPointerException if value is null
     */
    public static <T> Optional<T> of(T value) {
        return new Optional<>(value);
    }

 

　　/**
     * Constructs an instance with the value present.
     *
     * @param value the non-null value to be present
     * @throws NullPointerException if value is null
     */
    private Optional(T value) {
        this.value = Objects.requireNonNull(value);
    }

Objects.java

    /**
     * Checks that the specified object reference is not {@code null}. This
     * method is designed primarily for doing parameter validation in methods
     * and constructors, as demonstrated below:
     * <blockquote><pre>
     * public Foo(Bar bar) {
     *     this.bar = Objects.requireNonNull(bar);
     * }
     * </pre></blockquote>
     *
     * @param obj the object reference to check for nullity
     * @param <T> the type of the reference
     * @return {@code obj} if not {@code null}
     * @throws NullPointerException if {@code obj} is {@code null}
     */
    public static <T> T requireNonNull(T obj) {
        if (obj == null)
            throw new NullPointerException();
        return obj;
    }

 

三、解决方案

改用：Optional.ofNullable()

这个方案就直接判空返回，并不会直接报错，返回fasle后

Optional.ofNullable()源码

Optional.java

    /**
     * Returns an {@code Optional} describing the specified value, if non-null,
     * otherwise returns an empty {@code Optional}.
     *
     * @param <T> the class of the value
     * @param value the possibly-null value to describe
     * @return an {@code Optional} with a present value if the specified value
     * is non-null, otherwise an empty {@code Optional}
     */
    public static <T> Optional<T> ofNullable(T value) {
        return value == null ? empty() : of(value);
    }

 

这里使用了@SuppressWarnings("unchecked")：忽略 unchecked 警告

    /**
     * Common instance for {@code empty()}.
     */
    private static final Optional<?> EMPTY = new Optional<>();

　　/**
     * Returns an empty {@code Optional} instance.  No value is present for this
     * Optional.
     *
     * @apiNote Though it may be tempting to do so, avoid testing if an object
     * is empty by comparing with {@code ==} against instances returned by
     * {@code Option.empty()}. There is no guarantee that it is a singleton.
     * Instead, use {@link #isPresent()}.
     *
     * @param <T> Type of the non-existent value
     * @return an empty {@code Optional}
     */
    public static<T> Optional<T> empty() {
        @SuppressWarnings("unchecked")
        Optional<T> t = (Optional<T>) EMPTY;
        return t;
    }