一、defer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 rxJavaDeferExample() {
        Disposable disposable = Observable.defer(new Callable<ObservableSource<?>>() {
            @Override
            public ObservableSource<?> call() throws Exception {
                return model.getRxJavaCreateExampleData();
            }
        }).subscribeOn(Schedulers.io())
                .unsubscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Consumer<Object>() {
                    @Override
                    public void accept(Object o) throws Exception {
                        LogUtils.error(TAG, "rxJavaDeferExample--:" + Thread.currentThread().getName() + "-consumer-:" + o.toString());
                    }
                });
        compositeDisposable.add(disposable);
    }

日志

08-18 16:22:40.699 30806-31257/com.example.zhang D/MainModel: getRxJavaCreateExampleData---:RxCachedThreadScheduler-1--:1
08-18 16:22:40.700 30806-31257/com.example.zhang D/MainModel: getRxJavaCreateExampleData---:RxCachedThreadScheduler-1--:2
    getRxJavaCreateExampleData---:RxCachedThreadScheduler-1--:3
08-18 16:22:40.700 30806-30806/com.example.zhang E/MainPresenter: rxJavaDeferExample--:main-consumer-:1
08-18 16:22:40.700 30806-31257/com.example.zhang D/MainModel: getRxJavaCreateExampleData---:RxCachedThreadScheduler-1--:4
08-18 16:22:40.700 30806-30806/com.example.zhang E/MainPresenter: rxJavaDeferExample--:main-consumer-:2
    rxJavaDeferExample--:main-consumer-:3

总结

1、defer 就相当于懒加载，只有等observable 与observer建立了订阅关系时，observable才会建立