Java Null判断的替代方法

为了解决空指针的判断问题，Java引入了Optional、Objects等工具。 但平时比较费事的是对象以及对象属性的多级判断。 前几天看了一篇博文，作者通过借鉴Optional实现了多级null判断，这里自己也实现一下，且通过Junit5编写了测试用例。 github源码工程

Optional代码：

package org.yunzhong.CommonTest.util; import java.util.Objects; import java.util.function.Consumer; import java.util.function.Function; import java.util.function.Predicate; import java.util.function.Supplier; /** * @author yunzhong * * @param <T> */ public final class OptionalUtil<T> { private static final OptionalUtil<?> EMPTY = new OptionalUtil<>(); private final T value; private OptionalUtil() { this.value = null; } public OptionalUtil(T value) { this.value = value; } public static <T> OptionalUtil<T> of(T value) { return new OptionalUtil<>(Objects.requireNonNull(value)); } /** * @param <T> * @param value * @return */ public static <T> OptionalUtil<T> ofNullable(T value) { return value == null ? empty() : of(value); } /** * * 取出具体的值 * * @param fn * @param <R> * @return */ public T get() { return value; } /** * * 取出一个可能为空的对象 * * @param fn * @param <R> * @return */ public <R> OptionalUtil<R> getProperty(Function<? super T, ? extends R> fn) { return Objects.isNull(value) ? OptionalUtil.empty() : OptionalUtil.ofNullable(fn.apply(value)); } /** * 如果目标值不为空，返回value。<br> * 如果目标值为空,返回传入的默认值 * * @param defaultValue * @return */ public T orElse(T defaultValue) { return value != null ? value : defaultValue; } /** * 如果目标值不为空，返回value。<br> * 如果目标值为空 通过lambda表达式获取一个值 * * @param defaultSupplier * @return */ public T orElseGet(Supplier<? extends T> defaultSupplier) { return value != null ? value : defaultSupplier.get(); } /** * * 如果目标值为空 抛出一个异常 * * @param exceptionSupplier * @param <X> * @return * @throws X */ public <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier) throws X { if (value != null) { return value; } else { throw exceptionSupplier.get(); } } public boolean isPresent() { return value != null; } /** * @param consumer */ public void ifPresent(Consumer<? super T> consumer) { if (value != null) consumer.accept(value); } @Override public int hashCode() { return Objects.hashCode(value); } public OptionalUtil<T> filter(Predicate<? super T> predicate) { Objects.requireNonNull(predicate); if (!isPresent()) { return this; } else { return predicate.test(value) ? this : empty(); } } /** * 空值常量 * * @param <T> * @return */ @SuppressWarnings("unchecked") public static <T> OptionalUtil<T> empty() { OptionalUtil<T> none = (OptionalUtil<T>) EMPTY; return none; } }

测试用例：

package org.yunzhong.CommonTest.util; import static org.junit.jupiter.api.Assertions.assertEquals; import static org.junit.jupiter.api.Assertions.assertNotNull; import static org.junit.jupiter.api.Assertions.assertNull; import static org.junit.jupiter.api.Assertions.assertThrows; import org.junit.jupiter.api.AfterAll; import org.junit.jupiter.api.BeforeAll; import org.junit.jupiter.api.DisplayName; import org.junit.jupiter.api.Nested; import org.junit.jupiter.api.Test; @DisplayName("optional单元测试") public class OptionalUtilTest { @BeforeAll public static void beforeAll() { System.out.println("first of all."); } @AfterAll public static void afterAll() { System.out.println("after of all."); } @Nested @DisplayName("of方法单元测试") class OfTest { @Test @DisplayName("of方法正常") void testOf() { OptionalUtil<Double> value = OptionalUtil.of(Double.valueOf(12.2)); assertNotNull(value); assertEquals(12.2, value.get(), 1); } @Test @DisplayName("of方法null抛出异常") void testOfWithNull() { NullPointerException exception = assertThrows(NullPointerException.class, () -> OptionalUtil.of(null)); assertNotNull(exception); } } @Nested @DisplayName("ofNullable方法单元测试") class OfNullableTest { @Test @DisplayName("ofNullable方法正常") void testOf() { OptionalUtil<Double> value = OptionalUtil.ofNullable(Double.valueOf(12.2)); assertNotNull(value); assertEquals(12.2, value.get(), 1); } @Test @DisplayName("ofNullable方法null,get返回null") void testOfWithNull() { Object value = OptionalUtil.ofNullable(null).get(); assertNull(value); } } @Nested @DisplayName("getProperty方法单元测试") class GetPropertyTest { class TestModel { private String id; private String name; private TestModel model; public String getId() { return id; } public void setId(String id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public TestModel getModel() { return model; } public void setModel(TestModel model) { this.model = model; } } @Test @DisplayName("getProperty方法正常") void testgetProperty() { TestModel model = new TestModel(); model.setId("id1"); model.setName("name1"); TestModel modelInner = new TestModel(); modelInner.setId("innerId"); modelInner.setName("innerName"); model.setModel(modelInner); String result = OptionalUtil.ofNullable(model).getProperty(TestModel::getModel) .getProperty(TestModel::getId).get(); assertEquals("innerId", result); } @Test @DisplayName("getProperty方法null,get返回null") void testgetPropertyNull() { TestModel model = new TestModel(); model.setId("id1"); model.setName("name1"); String result = OptionalUtil.ofNullable(model).getProperty(TestModel::getModel) .getProperty(TestModel::getId).get(); assertNull(result); } } @Test @DisplayName("OrElse方法") void testOrElse() { Double orElse = OptionalUtil.ofNullable(Double.valueOf(12)).orElse(100.0); assertEquals(12, orElse, 0); Double param = null; Double orElse2 = OptionalUtil.ofNullable(param).orElse(100.0D); assertEquals(100, orElse2, 0); } @Test @DisplayName("OrElseGet方法") void testOrElseGet() { Double orElse = OptionalUtil.ofNullable(Double.valueOf(12)).orElseGet(() -> { return 10 * 12D; }); assertEquals(12, orElse, 0); Double param = null; Double orElse2 = OptionalUtil.ofNullable(param).orElseGet(() -> { return 10 * 12D; }); assertEquals(120, orElse2, 0); } @Test @DisplayName("OrElseThrow单元测试") void testOrElseThrow() { Double param = null; NullPointerException assertThrows = assertThrows(NullPointerException.class, () -> OptionalUtil.ofNullable(param).orElseThrow(() -> new NullPointerException())); assertNotNull(assertThrows); } @Test @DisplayName("IsPresent单元测试") void testIsPresent() { boolean present = OptionalUtil.ofNullable(Double.valueOf(33)).isPresent(); assertEquals(true, present); present = OptionalUtil.ofNullable(null).isPresent(); assertEquals(false, present); } @Test @DisplayName("IfPresent单元测试") void testIfPresent() { OptionalUtil.ofNullable(Double.valueOf(33)).ifPresent((value) -> { System.out.println(value); }); } @Nested @DisplayName("Filter单元测试") class FilterTest { @Test @DisplayName("Filter null 单元测试") void testFilterNull() { Object result = OptionalUtil.ofNullable(null).filter((value) -> { if (value == null) { return true; } else { return false; } }).get(); assertNull(result); } @Test @DisplayName("Filter null 单元测试") void testFilter() { Double param = 100D; Double result = OptionalUtil.ofNullable(param).filter((value) -> { if (value > 10) { return true; } else { return false; } }).get(); assertEquals(100D, result, 1); param = 3D; result = OptionalUtil.ofNullable(param).filter((value) -> { if (value > 10) { return true; } else { return false; } }).get(); assertNull(result); } } }