RxAndroid的map通过Function把一个对象转换为另外一个对象，作为结果输出。flatMap则可以通俗的理解为把一个集合元素对象拆分成单个元素对象，然后丢给Observer作为输入。例子：

package zhangphil.app;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

import java.util.Arrays;
import java.util.List;

import io.reactivex.Observable;
import io.reactivex.android.schedulers.AndroidSchedulers;
import io.reactivex.functions.Function;
import io.reactivex.observers.DisposableObserver;
import io.reactivex.schedulers.Schedulers;

public class MainActivity extends Activity {

    //假设一个数据源
    private String TAG = "zhangphil测试";

    private DisposableObserver<String> observer = new DisposableObserver<String>() {

        @Override
        public void onNext(String s) {
            Log.d(TAG, "onNext - Start");
            Log.d(TAG, String.valueOf(s));
            Log.d(TAG, "onNext - End");
        }

        @Override
        public void onComplete() {
            Log.d(TAG, "onComplete");
        }

        @Override
        public void onError(Throwable e) {
            Log.e(TAG, e.toString(), e);
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        String[] source = {"zhang", "phil", "@", "csdn"};
        List<String> lists = Arrays.asList(source);

        Observable
                .just(lists)
                .subscribeOn(Schedulers.io())//执行任务的线程
                .observeOn(AndroidSchedulers.mainThread())//回调发生的线程
                .flatMap(function)
                .subscribe(observer);
    }

    // 设置映射函数
    private Function<List<String>, Observable<String>> function = new Function<List<String>, Observable<String>>() {
        @Override
        public Observable<String> apply(List<String> lists) {
            String[] strs = new String[lists.size()];
            for (int i = 0; i < lists.size(); i++) {
                strs[i] = lists.get(i).toUpperCase();
            }
            return Observable.fromArray(strs);
        }
    };
}

 

代码运行结果输出：

 

03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: onNext - Start
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: ZHANG
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: onNext - End
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: onNext - Start
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: PHIL
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: onNext - End
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: onNext - Start
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: @
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: onNext - End
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: onNext - Start
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: CSDN
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: onNext - End
03-02 10:31:06.606 18037-18037/zhangphil.app D/zhangphil测试: onComplete