首先放jdk18的官方特性介绍地址：https://openjdk.java.net/jeps/420
我就不再过多解释了，直接贴代码吧~
代码语言：javascript复制package cn.hutool.core.lang;
import cn.hutool.core.lang.func.Func1;
import cn.hutool.core.lang.func.LambdaUtil;
import cn.hutool.core.lang.func.VoidFunc1;
import java.util.Arrays;
import java.util.Objects;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
/**
* 在不考虑性能的前提下，尽可能实现 JEP 420: Pattern Matching for switch,这是jdk18即将发布的新特性的变种写法
* 类型转换 instanceOf 老写法如下：
* <pre>{@code
* public static String formatter(Object o) {
* String formatted = "unknown";
* if (o instanceof Integer) {
* Integer i = (Integer) o;
* formatted = String.format("int %d", i);
* } else if (o instanceof Long) {
* Long l = (Long) o;
* formatted = String.format("long %d", l);
* } else if (o instanceof Double) {
* Double d = (Double) o;
* formatted = String.format("double %f", d);
* } else if (o instanceof String) {
* String s = (String) o;
* formatted = String.format("String %s", s);
* }
* return formatted;
* }
* }</pre>
* {@link SwitchCase}用法为
* <pre>{@code
* static String formatterWithSwitchCase(Object o) {
* return SwitchCase.choose(o)
* .when((Integer i) -> String.format("int %d", i))
* .when((Long l) -> String.format("long %d", l))
* .when((Double d) -> String.format("double %f", d))
* .when((String s) -> String.format("String %s", s))
* .otherwise("unknown")
* .get();
* }
* }</pre>
* 然后对于一般条件且无返回值的情况：
* <pre>{@code
* SwitchCase.choose(str)
* .whenConsumer(s -> System.out.println("Oops"), null)
* .whenConsumer(s -> System.out.println("Great"), "Foo", "Bar")
* .otherwiseConsumer(s -> System.out.println("Ok"));
* }</pre>
*
* @author VampireAchao
* @since 2022/3/26 15:56
*/
@SuppressWarnings("unchecked")
public class SwitchCase<T> {
private final T source;
private boolean isMatched = false;
private boolean isDefault = false;
private final Class<T> type;
private SwitchCase(T source) {
this.source = source;
this.type = source == null ? null : (Class<T>) source.getClass();
}
private SwitchCase(T source, boolean isMatched) {
this.source = source;
this.isMatched = isMatched;
this.type = source == null ? null : (Class<T>) source.getClass();
}
private SwitchCase(T source, boolean isMatched, boolean isDefault) {
this.source = source;
this.isMatched = isMatched;
this.isDefault = isDefault;
this.type = source == null ? null : (Class<T>) source.getClass();
}
public T get() {
return source;
}
public boolean isMatched() {
return isMatched;
}
public boolean isDefault() {
return isDefault;
}
public Class<T> getType() {
return type;
}
public static <T> SwitchCase<T> choose(T obj) {
return new SwitchCase<>(obj);
}
/**
* 传入lambda，根据类型自动完成匹配
*
* @param function lambda，例如 {@code (Integer i) -> String.format("int %d", i)}
* @param <S> lambda指定的参数类型
* @param <R> lambda指定的返回值类型
* @param <O> 实际的类型
* @return 匹配后封装的 {@link SwitchCase}
*/
public <S, R, O> SwitchCase<O> when(Func1<S, R> function) {
if (false == isMatched && LambdaUtil.getRealClass(function).isInstance(source)) {
return new SwitchCase<>((O) function.callWithRuntimeException((S) source), true);
}
return (SwitchCase<O>) this;
}
/**
* 传入lambda，根据类型自动完成匹配
*
* @param consumer lambda，例如 {@code (Integer i) -> Console.log("int {}", i)}
* @param <S> lambda指定的参数类型
* @param <O> 实际的类型
* @return 匹配后封装的 {@link SwitchCase}
*/
public <S, O> SwitchCase<O> whenConsumer(VoidFunc1<S> consumer) {
if (false == isMatched && LambdaUtil.getRealClassConsumer(consumer).isInstance(source)) {
consumer.callWithRuntimeException((S) source);
return new SwitchCase<>((O) source, true);
}
return (SwitchCase<O>) this;
}
/**
* 传入lambda，根据条件自动完成匹配
*
* @param condition 可传入条件表达式，例如{@code v -> ObjectUtil.isNotNull(v) && "hutool".equals(v)}
* @param function 需要进行的操作
* @param <R> 操作返回值
* @param <O> 实际的类型
* @return 匹配后封装的 {@link SwitchCase}
*/
public <R, O> SwitchCase<O> when(Predicate<T> condition, Function<T, R> function) {
if (false == isMatched && condition.test(source)) {
return new SwitchCase<>((O) function.apply(source), true);
}
return (SwitchCase<O>) this;
}
/**
* 传入lambda，根据条件自动完成匹配
*
* @param compare 比较的值
* @param function 需要进行的操作
* @param <R> 操作返回值
* @param <O> 实际的类型
* @return 匹配后封装的 {@link SwitchCase}
*/
public <R, O> SwitchCase<O> when(T compare, Function<T, R> function) {
return when(function, compare);
}
/**
* 传入lambda，根据条件自动完成匹配，由于动态参数只能放在最后，不得不调整下参数顺序
*
* @param function 需要进行的操作
* @param compares 需要匹配的参数
* @param <R> 操作返回值
* @param <O> 实际的类型
* @return 匹配后封装的 {@link SwitchCase}
*/
public <R, O> SwitchCase<O> when(Function<T, R> function, T... compares) {
if (false == isMatched && Arrays.asList(compares).contains(source)) {
return new SwitchCase<>((O) function.apply(source), true);
}
return (SwitchCase<O>) this;
}
/**
* 传入lambda，根据条件自动完成匹配，由于动态参数只能放在最后，不得不调整下参数顺序
*
* @param consumer 需要进行的操作
* @param compares 需要匹配的参数
* @return 匹配后封装的 {@link SwitchCase}
*/
public SwitchCase<T> whenConsumer(Consumer<T> consumer, T... compares) {
if (false == isMatched
&& (compares == null && source == null)
|| (compares != null && Arrays.asList(compares).contains(source))) {
consumer.accept(source);
return new SwitchCase<>(source, true);
}
return this;
}
/**
* 传入lambda，根据条件自动完成匹配
*
* @param condition 可传入条件表达式，例如{@code v -> ObjectUtil.isNotNull(v) && "hutool".equals(v)}
* @param consumer 需要进行的操作
* @return 匹配后封装的 {@link SwitchCase}
*/
public SwitchCase<T> whenPredicateConsumer(Predicate<T> condition, Consumer<T> consumer) {
if (false == isMatched && condition.test(source)) {
consumer.accept(source);
return new SwitchCase<>(source, true);
}
return this;
}
/**
* 如果其他条件不满足，则执行
*
* @param function 想要执行的lambda
* @param <O> 返回值类型
* @return 匹配后封装的 {@link SwitchCase}
*/
public <O> SwitchCase<O> otherwise(UnaryOperator<O> function) {
if (false == isMatched) {
return new SwitchCase<>(function.apply((O) source), false, true);
}
return (SwitchCase<O>) this;
}
/**
* 如果其他条件不满足，则提供该默认值
*
* @param value 默认值
* @param <O> 返回值类型
* @return 匹配后封装的 {@link SwitchCase}
*/
public <O> SwitchCase<O> otherwise(O value) {
if (false == isMatched) {
return new SwitchCase<>(value, false, true);
}
return (SwitchCase<O>) this;
}
/**
* 如果其他条件不满足，则执行
*
* @param consumer 想要执行的lambda
* @return 匹配后封装的 {@link SwitchCase}
*/
public SwitchCase<T> otherwiseConsumer(Consumer<T> consumer) {
if (false == isMatched) {
consumer.accept(source);
return new SwitchCase<>(source, false, true);
}
return this;
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (!(o instanceof SwitchCase)) {
return false;
}
return Objects.equals(((SwitchCase<?>) o).get(), source);
}
@Override
public String toString() {
return String.valueOf(source);
}
}然后其中用到了LambdaUtil，自己额外新增了一个方法，其余的在hutool5.8版本
/**
* 通过对象的方法或类的静态方法引用，然后根据{@link SerializedLambda#getInstantiatedMethodType()}获取lambda实现类<br>
* 传入lambda有参数且无返回值的情况能够匹配到此方法：
*
* @param func lambda
* @param <P> 方法调用方类型
* @return lambda实现类
* @throws IllegalArgumentException 如果是不支持的方法引用，抛出该异常，见{@link LambdaUtil#checkLambdaTypeCanGetClass}
*/
public static <P> Class<P> getRealClassConsumer(VoidFunc1<P> func) {
SerializedLambda lambda = _resolve(func);
checkLambdaTypeCanGetClass(lambda.getImplMethodKind());
String instantiatedMethodType = lambda.getInstantiatedMethodType();
return ClassUtil.loadClass(StrUtil.sub(instantiatedMethodType, 2, StrUtil.indexOf(instantiatedMethodType, ';')));
}接下来是用法
代码语言：javascript复制package cn.hutool.core.lang;
import cn.hutool.core.util.ObjectUtil;
import cn.hutool.core.util.StrUtil;
import org.junit.Assert;
import org.junit.Test;
/**
* SwitchCaseTest
*
* @author VampireAchao
* @since 2022/3/26 15:57
*/
public class SwitchCaseTest {
/**
* 老写法
*/
public static String formatter(Object o) {
String formatted = "unknown";
if (o instanceof Integer) {
Integer i = (Integer) o;
formatted = String.format("int %d", i);
} else if (o instanceof Long) {
Long l = (Long) o;
formatted = String.format("long %d", l);
} else if (o instanceof Double) {
Double d = (Double) o;
formatted = String.format("double %f", d);
} else if (o instanceof String) {
String s = (String) o;
formatted = String.format("String %s", s);
}
return formatted;
}
/**
* 新写法,{@see https://openjdk.java.net/jeps/420}
*/
public static String formatterWithSwitchCase(Object o) {
return SwitchCase.choose(o)
.when((Integer i) -> String.format("int %d", i))
.when((Long l) -> String.format("long %d", l))
.when((Double d) -> String.format("double %f", d))
.when((String s) -> String.format("String %s", s))
.otherwise("unknown")
.get();
}
public static void formatterWithSwitchCaseConsumer(Object o) {
SwitchCase.choose(o)
.whenConsumer((Integer i) -> Console.log("int {}", i))
.whenConsumer((Long l) -> Console.log("long {}", l))
.whenConsumer((Double d) -> Console.log("double {}", d))
.whenConsumer((String s) -> Console.log("String {}", s))
.otherwise(s -> "unknown")
.get();
}
static void testFooBar(String str) {
/*switch (s) {
case null -> System.out.println("Oops");
case "Foo", "Bar" -> System.out.println("Great");
default -> System.out.println("Ok");
}*/
SwitchCase.choose(str)
.whenConsumer(s -> System.out.println("Oops"), null)
.whenConsumer(s -> System.out.println("Great"), "Foo", "Bar")
.otherwiseConsumer(s -> System.out.println("Ok"));
}
@Test
public void testWhenConsumer() {
testFooBar(null);
testFooBar("Foo");
testFooBar("");
}
@Test
public void whenTest() {
Assert.assertTrue(SwitchCase.choose(Class.class).when((Class<?> cls) -> cls).isMatched());
Assert.assertFalse(SwitchCase.choose(0).when((String s) -> s).isMatched());
Assert.assertTrue(SwitchCase.choose(Class.class).whenConsumer((Class<?> cls) -> Console.log()).isMatched());
Assert.assertFalse(SwitchCase.choose(0).whenConsumer((String s) -> Console.log()).isMatched());
Assert.assertTrue(SwitchCase.choose("ruben").when("x", s -> s).otherwise(s -> s).isDefault());
Assert.assertFalse(SwitchCase.choose("ruben").when("ruben", s -> s).isDefault());
Assert.assertEquals("Feature",
SwitchCase.choose("hutool")
.when(
// 条件
v -> ObjectUtil.isNotNull(v) && "hutool".equals(v),
// 实际操作
s -> "Feature"
).get());
}
}
