RxJava中的map通过Function（函数）做一次结果转换，例如把输入源的数据转换处理成大写：

package zhangphil.app;

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

import io.reactivex.Observable;
import io.reactivex.Observer;
import io.reactivex.android.schedulers.AndroidSchedulers;
import io.reactivex.disposables.Disposable;
import io.reactivex.functions.Function;
import io.reactivex.schedulers.Schedulers;

public class MainActivity extends Activity {

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

    Observer<String> observer = new Observer<String>() {
        @Override
        public void onSubscribe(Disposable d) {
            //Log.d(TAG, d.toString());
        }

        @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);

        //为一个数据源增加一个观察者
        //观察者是observer，observer吐出观察到的数据
        Observable
                .just("zhang", "phil", "@", "csdn")
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .map(function)
                .subscribe(observer);
    }

    private Function<String, String> function = new Function<String, String>() {
        @Override
        public String apply(String s) throws Exception {
            return s.toUpperCase();
        }
    };
}

代码运行结果输出：

 

03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: onNext - Start
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: ZHANG
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: onNext - End
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: onNext - Start
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: PHIL
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: onNext - End
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: onNext - Start
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: @
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: onNext - End
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: onNext - Start
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: CSDN
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: onNext - End
03-01 20:32:09.354 1581-1581/zhangphil.app D/zhangphil: onComplete