类似于Guava Function实现

模拟实现Guava中，输入一个List<F>, 实现一个抽象方法，即可获取输出的List<T>. 即 List<F>   => List<T>.

注意，在远程调用RPC，例如navi-rpc当中使用时，请不要使用Function以及Predicate返回的Collection、List等对象传输。

原因是navi-rpc使用的Runtimeprotobuf，会利用反射构造出属性未填充的空对象，然后再merge字节流进去，这时候如果是guava内部封装的内部类，而不是ArrayList等JDK实现类，会出现一些意外的错误，原因是guava的内部类有些是不支持添加修改操作的。

class Person implements Comparable<Person> {

    private String name;
    private int age;

    /**
     * @param name
     * @param age
     */
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * @return the age
     */
    public int getAge() {
        return age;
    }

    /**
     * @param age the age to set
     */
    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public int hashCode() {
        return Objects.hashCode(age, name);
    }

    @Override
    public boolean equals(Object obj) {
        if (obj instanceof Person) {
            Person that = (Person) obj;
            return Objects.equal(age, that.age) && Objects.equal(name, that.name);
        }

        return false;
    }

    @Override
    public String toString() {
        return Objects.toStringHelper(this).add("name", name).add("age", age).toString();
    }

    @Override
    public int compareTo(Person o) {
        return ComparisonChain.start().compare(name, o.name).compare(age, o.age).result();
    }

}

import java.util.Iterator;import java.util.List;import java.util.RandomAccess;import com.google.common.base.Objects;import com.google.common.collect.ComparisonChain;import com.google.common.collect.Lists;public class TestMain {    public static void main(String[] args) {                /******************** 初始化数据 ************************/                List<Person> persionArrayList = Lists.newArrayList();        persionArrayList.add(new Person("peter", 12));        persionArrayList.add(new Person("tony", 24));        persionArrayList.add(null);        persionArrayList.add(new Person("jason", 11));        persionArrayList.add(new Person("tomson", 21));                List<Person> persionLinkedList = Lists.newLinkedList();        persionLinkedList.add(new Person("peter", 12));        persionLinkedList.add(new Person("tony", 24));        persionLinkedList.add(null);        persionLinkedList.add(new Person("jason", 11));        persionLinkedList.add(new Person("tomson", 21));        /******************** 实现抽象并调用 ************************/        List<String> nameList = myTransform(persionLinkedList, new FTWork<Person, String>() {            @Override            public String apply(Person acc) {                return acc == null ? "" : acc.getName();            }        });        /******************** 实现抽象并调用 ************************/        List<Integer> ageList = myTransform(persionArrayList, new FTWork<Person, Integer>() {            @Override            public Integer apply(Person acc) {                return acc == null ? -1 : acc.getAge();            }        });        System.out.println(nameList);        System.out.println(ageList);    }    /**     * 进行转化的方法     *      * @param fromList 需要进行转化的对象集合     * @param work 抽象工作类     * @return List<T> 转化后的结果集     *     * @author zhoudongdong     */    public static <F, T> List<T> myTransform(List<F> fromList, FTWork<? super F, ? extends T> work) {        List<T> resultList = Lists.<T> newArrayList();                if (fromList instanceof RandomAccess) {            System.out.println("instanceof RandomAccess ...");                        for (int i = 0; i < fromList.size(); ++i) {                resultList.add((T) work.apply(fromList.get(i)));            }        } else {            System.out.println("instanceof SequenceList ...");                        for (Iterator<F> itr = fromList.iterator(); itr.hasNext();) {                resultList.add((T) work.apply(itr.next()));            }        }        return resultList;    }        /**     * 工作抽象类     * <p>     *     * @author zhoudongdong     */    static abstract class FTWork<F, T> {                public abstract T apply(F f);    }}

输出结果：

instanceof SequenceList ...
instanceof RandomAccess ...
[peter, tony, , jason, tomson]
[12, 24, -1, 11, 21]