Guava之FluentIterable使用示例
FluentIterable 是guava集合类中常用的一个类，主要用于过滤、转换集合中的数据；FluentIterable是一个抽象类，实现了Iterable接口，大多数方法都返回FluentIterable对象，这也是guava的思想之一。
transform：对于ListenableFuture的返回值进行转换。
allAsList：对多个ListenableFuture的合并，返回一个当所有Future成功时返回多个Future返回值组成的List对象。注：当其中一个Future失败或者取消的时候，将会进入失败或者取消。
successfulAsList：和allAsList相似，唯一差别是对于失败或取消的Future返回值用null代替。不会进入失败或者取消流程。
immediateFuture/immediateCancelledFuture： 立即返回一个待返回值的ListenableFuture。
makeChecked: 将ListenableFuture 转换成CheckedFuture。CheckedFuture 是一个ListenableFuture ，其中包含了多个版本的get 方法，方法声明抛出检查异常.这样使得创建一个在执行逻辑中可以抛出异常的Future更加容易
JdkFutureAdapters.listenInPoolThread(future): guava同时提供了将JDK Future转换为ListenableFuture的接口函数。
addCallBack为Future增加回调
首先构造集合中的元素类型
public class User {
private int age;
private String name;
public User() {
}
public User(int age, String name) {
this.age = age;
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
final StringBuilder sb = new StringBuilder("User{");
sb.append("age=").append(age);
sb.append(", name='").append(name).append('\'');
sb.append('}');
return sb.toString();
}
}
常用方法
1.过滤(filter)元素
filter方法要接收Predicate接口
/**
* Returns the elements from this fluent iterable that satisfy a predicate.
* The resulting fluent iterable's iterator does not support remove().
*/
public final FluentIterable<E> filter(Predicate<? super E> predicate) {
return from(Iterables.filter(getDelegate(), predicate));
}
/**
* Returns the elements from this fluent iterable that are instances of class type.
*
*/
@GwtIncompatible // Class.isInstance
public final <T> FluentIterable<T> filter(Class<T> type) {
return from(Iterables.filter(getDelegate(), type));
}
过滤出年龄是20岁的用户
public class Test {
public static void main(String[] args) {
List<User> userList = Lists.newArrayList();
userList.add(new User(18, "zhangsan"));
userList.add(new User(20, "lisi"));
userList.add(new User(22, "wangwu"));
FluentIterable<User> filter = FluentIterable.from(userList).filter(
new Predicate<User>() {
@Override
public boolean apply(User user) {
return user.getAge() == 20;
}
});
for (User user : filter) {
System.out.println(user);
}
}
}
打印效果：
User{age=20, name='lisi'}
这里有一个潜在的坑，在高版本(21.0++)的guava中Predicate接口继承了java 8中的java.util.function.Predicate
@FunctionalInterface @GwtCompatible public interface Predicate<T> extends java.util.function.Predicate<T>
2.转换(transform)集合类型，transform接收Function接口,一般在方法中采用new接口实现回调方法apply的方式。
/**
* Returns a fluent iterable that applies function to each element of this fluent
* iterable.
*
* <p>The returned fluent iterable's iterator supports remove() if this iterable's
* iterator does. After a successful remove() call, this fluent iterable no longer
* contains the corresponding element.
*/
public final <T> FluentIterable<T> transform(Function<? super E, T> function) {
return from(Iterables.transform(getDelegate(), function));
}
public class Test {
public static void main(String[] args) {
List<User> userList = Lists.newArrayList();
userList.add(new User(18, "zhangsan"));
userList.add(new User(20, "lisi"));
userList.add(new User(22, "wangwu"));
FluentIterable<String> transform = FluentIterable.from(userList).transform(
new Function<User, String>() {
@Override
public String apply(User user) {
return Joiner.on(",").join(user.getName(), user.getAge());
}
});
for (String user : transform) {
System.out.println(user);
}
}
}
打印效果
zhangsan,18 lisi,20 wangwu,22
Function接口的定义
public interface Function<F, T>
From-->To
拿到所有用户的年龄
public class Test {
public static void main(String[] args) {
List<User> userList = Lists.newArrayList();
userList.add(new User(18, "zhangsan"));
userList.add(new User(20, "lisi"));
userList.add(new User(22, "wangwu"));
List<Integer> ages = FluentIterable.from(userList).transform(
new Function<User, Integer>() {
@Override
public Integer apply(User input) {
return input.getAge();
}
}).toList();
System.out.println(ages);
}
}
打印结果
[18, 20, 22]
public final class Test {
public static <F, T> void main(String[] args) {
List<F> fromList = new ArrayList<F>();
List<T> result = FluentIterable.from(fromList).transform(new Function<F, T>() {
@Override
public T apply(F input) {
// 可以根据需要写一个转换器
// 将类型F转换成T
return XXConverter.convert(input);
}
}).toList();
}
}
class XXConverter<F, T> {
public static <F, T> T convert(F f) {
return null;
}
}
3.集合中的元素是否都满足某个条件
/**
* Returns true if every element in this fluent iterable satisfies the predicate. If this
* fluent iterable is empty, true is returned.
*/
public final boolean allMatch(Predicate<? super E> predicate) {
return Iterables.all(getDelegate(), predicate);
}
public class Test {
public static void main(String[] args) {
List<User> userList = Lists.newArrayList();
userList.add(new User(18, "zhangsan"));
userList.add(new User(20, "lisi"));
userList.add(new User(22, "wangwu"));
boolean allMatch = FluentIterable.from(userList).allMatch(
new Predicate<User>() {
@Override
public boolean apply(User input) {
return input.getAge() >= 18;
}
});
//true
System.out.println(allMatch);
}
}
4.集合中的任何一个元素满足指定的条件即可
/**
* Returns true if any element in this fluent iterable satisfies the predicate.
*/
public final boolean anyMatch(Predicate<? super E> predicate) {
return Iterables.any(getDelegate(), predicate);
}
public class Test {
public static void main(String[] args) {
List<User> userList = Lists.newArrayList();
userList.add(new User(18, "zhangsan"));
userList.add(new User(20, "lisi"));
userList.add(new User(22, "wangwu"));
boolean allMatch = FluentIterable.from(userList).anyMatch(
new Predicate<User>() {
@Override
public boolean apply(User input) {
return input.getAge() >= 22;
}
});
//true
System.out.println(allMatch);
}
}
转载自：https://www.cnblogs.com/winner-0715/p/8412655.html
