总结：

1、FlatMap 可以把一个发射器 Observable 通过某种方法转换为多个 Observables，然后再把这些分散的 Observables装进一个单一的发射器 Observable。但有个需要注意的是，flatMap 并不能保证事件的顺序
2、concatMap 与 FlatMap 的唯一区别就是 concatMap 保证了顺序

一、FlatMap语法

    public Observable<Integer> getRxJavaCreateExampleData() {
        return Observable.create(new ObservableOnSubscribe<Integer>() {
            @Override
            public void subscribe(ObservableEmitter<Integer> emitter) {
                LogUtils.debug(TAG, "getRxJavaCreateExampleData---:" + Thread.currentThread().getName() + "--:" + 1);
                emitter.onNext(1);

                LogUtils.debug(TAG, "getRxJavaCreateExampleData---:" + Thread.currentThread().getName() + "--:" + 2);
                emitter.onNext(2);

                LogUtils.debug(TAG, "getRxJavaCreateExampleData---:" + Thread.currentThread().getName() + "--:" + 3);
                emitter.onNext(3);
                emitter.onComplete();
                LogUtils.debug(TAG, "getRxJavaCreateExampleData---:" + Thread.currentThread().getName() + "--:" + 4);
                emitter.onNext(4);

            }
        });
    }

  public void rxJavaFlatMapExample() {
        Disposable disposable = model.getRxJavaCreateExampleData()
                .subscribeOn(Schedulers.io())
                .unsubscribeOn(Schedulers.io())
                .flatMap(new Function<Integer, ObservableSource<String>>() {
                    @Override
                    public ObservableSource<String> apply(Integer integer) throws Exception {
                        LogUtils.error(TAG, "rxJavaFlatMapExample--flatmap--:" + Thread.currentThread().getName() + "--:" + integer);
                        List<String> list = new ArrayList<>();
                        for (int i = 0; i < 3; i++) {
                            list.add("this is flatMap--" + integer + "---i--:" + i);
                        }
                        long delayTime = 1 + (int) (10 * Math.random());
                        return Observable.fromIterable(list).delay(delayTime, TimeUnit.SECONDS);
                    }
                }).observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer<String>() {
                    @Override
                    public void accept(String s) throws Exception {
                        LogUtils.error(TAG, "rxJavaFlatMapExample--Consumer--:" + Thread.currentThread().getName() + "--:" + s);
                    }
                });
        compositeDisposable.add(disposable);
    }

日志

08-08 17:28:30.149 15730-16292/com.example.zhang D/MainModel: getRxJavaCreateExampleData---:RxCachedThreadScheduler-2--:1
08-08 17:28:30.149 15730-16292/com.example.zhang E/MainPresenter: rxJavaFlatMapExample--flatmap--:RxCachedThreadScheduler-2--:1
08-08 17:28:30.150 15730-16292/com.example.zhang D/MainModel: getRxJavaCreateExampleData---:RxCachedThreadScheduler-2--:2
08-08 17:28:30.150 15730-16292/com.example.zhang E/MainPresenter: rxJavaFlatMapExample--flatmap--:RxCachedThreadScheduler-2--:2
08-08 17:28:30.151 15730-16292/com.example.zhang D/MainModel: getRxJavaCreateExampleData---:RxCachedThreadScheduler-2--:3
08-08 17:28:30.151 15730-16292/com.example.zhang E/MainPresenter: rxJavaFlatMapExample--flatmap--:RxCachedThreadScheduler-2--:3
08-08 17:28:30.152 15730-16292/com.example.zhang D/MainModel: getRxJavaCreateExampleData---:RxCachedThreadScheduler-2--:4
08-08 17:28:31.154 15730-15730/com.example.zhang E/MainPresenter: rxJavaFlatMapExample--Consumer--:main--:this is flatMap--3---i--:0
    rxJavaFlatMapExample--Consumer--:main--:this is flatMap--3---i--:1
08-08 17:28:31.155 15730-15730/com.example.zhang E/MainPresenter: rxJavaFlatMapExample--Consumer--:main--:this is flatMap--3---i--:2
08-08 17:28:36.150 15730-15730/com.example.zhang E/MainPresenter: rxJavaFlatMapExample--Consumer--:main--:this is flatMap--1---i--:0
08-08 17:28:36.151 15730-15730/com.example.zhang E/MainPresenter: rxJavaFlatMapExample--Consumer--:main--:this is flatMap--1---i--:1
    rxJavaFlatMapExample--Consumer--:main--:this is flatMap--1---i--:2
08-08 17:28:38.153 15730-15730/com.example.zhang E/MainPresenter: rxJavaFlatMapExample--Consumer--:main--:this is flatMap--2---i--:0
08-08 17:28:38.154 15730-15730/com.example.zhang E/MainPresenter: rxJavaFlatMapExample--Consumer--:main--:this is flatMap--2---i--:1
    rxJavaFlatMapExample--Consumer--:main--:this is flatMap--2---i--:2

二、ConcatMap语法练习

    public void rxJavaConcatMapExample() {
        Disposable disposable = model.getRxJavaCreateExampleData()
                .subscribeOn(Schedulers.io())
                .unsubscribeOn(Schedulers.io())
                .concatMap(new Function<Integer, ObservableSource<String>>() {
                    @Override
                    public ObservableSource<String> apply(Integer integer) throws Exception {
                        LogUtils.error(TAG, "rxJavaConcatMapExample--flatmap--:" + Thread.currentThread().getName() + "--:" + integer);
                        List<String> list = new ArrayList<>();
                        for (int i = 0; i < 3; i++) {
                            list.add("this is ConcatMap--" + integer + "---i--:" + i);
                        }
                        long delayTime = 1 + (int) (10 * Math.random());
                        return Observable.fromIterable(list).delay(delayTime, TimeUnit.SECONDS);//delay方法内部切换了线程
                    }
                }).observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer<String>() {
                    @Override
                    public void accept(String s) throws Exception {
                        LogUtils.error(TAG, "rxJavaConcatMapExample--Consumer--:" + Thread.currentThread().getName() + "--:" + s);
                    }
                });
        compositeDisposable.add(disposable);
    }

日志

08-08 17:37:17.486 18155-18519/com.example.zhang D/MainModel: getRxJavaCreateExampleData---:RxCachedThreadScheduler-1--:1
08-08 17:37:17.487 18155-18519/com.example.zhang E/MainPresenter: rxJavaConcatMapExample--flatmap--:RxCachedThreadScheduler-1--:1
08-08 17:37:17.492 18155-18519/com.example.zhang D/MainModel: getRxJavaCreateExampleData---:RxCachedThreadScheduler-1--:2
    getRxJavaCreateExampleData---:RxCachedThreadScheduler-1--:3
    getRxJavaCreateExampleData---:RxCachedThreadScheduler-1--:4
08-08 17:37:23.494 18155-18520/com.example.zhang E/MainPresenter: rxJavaConcatMapExample--flatmap--:RxComputationThreadPool-1--:2
08-08 17:37:23.494 18155-18155/com.example.zhang E/MainPresenter: rxJavaConcatMapExample--Consumer--:main--:this is ConcatMap--1---i--:0
    rxJavaConcatMapExample--Consumer--:main--:this is ConcatMap--1---i--:1
    rxJavaConcatMapExample--Consumer--:main--:this is ConcatMap--1---i--:2
08-08 17:37:25.496 18155-18155/com.example.zhang E/MainPresenter: rxJavaConcatMapExample--Consumer--:main--:this is ConcatMap--2---i--:0
08-08 17:37:25.501 18155-18155/com.example.zhang E/MainPresenter: rxJavaConcatMapExample--Consumer--:main--:this is ConcatMap--2---i--:1
08-08 17:37:25.501 18155-18527/com.example.zhang E/MainPresenter: rxJavaConcatMapExample--flatmap--:RxComputationThreadPool-2--:3
08-08 17:37:25.501 18155-18155/com.example.zhang E/MainPresenter: rxJavaConcatMapExample--Consumer--:main--:this is ConcatMap--2---i--:2
08-08 17:37:32.504 18155-18155/com.example.zhang E/MainPresenter: rxJavaConcatMapExample--Consumer--:main--:this is ConcatMap--3---i--:0
    rxJavaConcatMapExample--Consumer--:main--:this is ConcatMap--3---i--:1
    rxJavaConcatMapExample--Consumer--:main--:this is ConcatMap--3---i--:2

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