Optional中flatMap和map的运用。

Author: enjoyCoding666

src/main/java/com/bean/Address.java

@@ -47,7 +47,11 @@ public void setCity(String city) {
 		this.city = city;
 	}
 
-	public Optional<String> getCity() {
-		return Optional.ofNullable(this.city);
+//	public Optional<String> getCity() {
+//		return Optional.ofNullable(this.city);
+//	}
+
+	public String getCity() {
+		return this.city;
 	}
 }

src/main/java/com/java8/optional/OptionalDemo.java

@@ -18,7 +18,7 @@ public class OptionalDemo {
 	/**
 	 * orElse(默认值)，如果Optional<T>封装的对象不存在值，则返回默认值。
 	 */
-	public static void orElseDemo() {
+	public  void orElseDemo() {
 //		Worker worker1=new Worker("123",18,"lin");
 		Worker worker1 = null;
 		Worker worker2 = new Worker("456", 28, "chen");
@@ -37,22 +37,22 @@ public static void orElseDemo() {
 	 * orElseGet()，如果Optional<T>封装的对象不存在值，则执行Supplier函数式。
 	 * orElseGet(Supplier<? extends T> other)，返回的类型必须和Optional封装的对象类型一致。
 	 */
-	public static void ofElseGetDemo() {
+	public  void ofElseGetDemo() {
 		String name1 = null;
 		String name2 = "lin";
 		//orElseGet(Supplier<? extends T> other)，返回的类型必须和Optional封装的对象类型一致。
-		String result = Optional.ofNullable(name1).orElseGet(OptionalDemo::supplier);
+		String result = Optional.ofNullable(name1).orElseGet(this::supplier);
 		System.out.println(result);
 	}
 
-	public static String supplier() {
+	public  String supplier() {
 		return "orElseGet(Supplier)";
 	}
 
 	/**
 	 * of(对象)，如果封装的对象为空，则会报出空指针异常
 	 */
-	public static void ofDemo() {
+	public  void ofDemo() {
 //		Worker worker1=new Worker("123",18,"lin");
 		Worker worker1 = null;
 		Worker worker2 = new Worker("456", 28, "chen");
@@ -63,7 +63,7 @@ public static void ofDemo() {
 	/**
 	 * isPresent()表示如果Optional<T>封装的对象不为空，就返回true。
 	 */
-	public static void isPresentDemo() {
+	public  void isPresentDemo() {
 		Worker worker1 = new Worker("123", 18, "lin");
 		Optional<Worker> workerOpt = Optional.ofNullable(worker1);
 		//这种写法比较丑，可以直接用下面的ifPresent()方法代替。
@@ -80,7 +80,7 @@ public static void isPresentDemo() {
 	/**
 	 * ifPresent()表示如果对象不为null，则会执行对应的lambda语句。
 	 */
-	public static void ifPresentDemo() {
+	public  void ifPresentDemo() {
 //		Address address=new Address("中国","广东","深圳");
 //		Worker worker1=new Worker("123",18,"lin",address);
 		Worker worker1 = new Worker("123", 18, "lin");
@@ -97,7 +97,7 @@ public static void ifPresentDemo() {
 	/**
 	 * 这种大量的判空代码很丑。
 	 */
-	public static void tooMuchNull(Worker worker) {
+	public  void tooMuchNull(Worker worker) {
 //		if (worker != null) {
 //			Address address=worker.getAddress();
 //			if (address != null) {
@@ -106,26 +106,50 @@ public static void tooMuchNull(Worker worker) {
 //		}
 	}
 
+	public void mapDemo() {
+		Worker worker = new Worker("123", 18, "lin");
+		String name = Optional.ofNullable(worker).map(Worker::getName).orElse("");
+		System.out.println(name);
+
+	}
+
+
+	public  void mapDemo2() {
+		String str=" test ";
+		Optional.ofNullable(str).map(String::trim)
+				.filter(t -> t.length()> 1)
+				.ifPresent(s->{
+					s+="1234";
+					System.out.println(s);
+				});
+		//相当于以下代码：
+//		if (str != null) {
+//			str=str.trim();
+//			if (str.length() > 1) {
+//				str+="1234";
+//				System.out.println(str);
+//			}
+//		}
+	}
 
 	/**
 	 * flatMap()，如果Optional封装对象不为空，就会执行对应的mapping函数，返回Optional类型的值。
 	 * 否则就返回一个空的Optional对象。
 	 */
-	public static void flatMapDemo() {
+	public  void flatMapDemo() {
 		Address address = new Address("中国", "广东", "深圳");
 		Worker worker = new Worker("123", 18, "lin", address);
-		//默认值为"default"，有没有更好的选择？
 		String city = Optional.ofNullable(worker)
 				.flatMap(Worker::getAdress)
-				.flatMap(Address::getCity)
+				.map(Address::getCity)
 				.orElse("default");
 		System.out.println(city);
 	}
 
 	/**
 	 * orElseThrow(),如果Optional封装的对象为空，就会抛出对应的异常。
 	 */
-	public static void orElseThrowDemo() {
+	public  void orElseThrowDemo() {
 //		Worker worker = new Worker("123", 18, "lin");
 		Worker worker = null;
 		Worker result = Optional.ofNullable(worker)
@@ -134,7 +158,7 @@ public static void orElseThrowDemo() {
 	}
 
 
-	public static void filterDemo() {
+	public  void filterDemo() {
 		Worker worker = new Worker("123", 18, "lin");
 		Optional<Worker> result = Optional.ofNullable(worker)
 				.filter(worker1 -> worker1.getAge() > 20);