需求

查询用户最近的中奖信息 并返回中奖名单列表

纯Java7实现

// 返回用户最近4条的中奖纪录 List uwList = Lists.newArrayList(new UserWinning(userId, 1), new UserWinning(userId, 2), new UserWinning(userId, 3), new UserWinning(userId, 1)); //提取奖品ID List awardIdLsit = new ArrayList<>(uwList.size()); for(UserWinning uw : uwList){ awardIdLsit.add(uw.getAwardId()); } //根据奖品ID查询奖品 List awardList = Lists.newArrayList(new Award(1, "奖品一"), new Award(2, "奖品二"), new Award(3, "奖品三")); //List --> Map 得到奖品ID和奖品名称Map Map awardIdNameMap = new HashMap<>(awardList.size()); for(Award a : awardList){ awardIdNameMap.put(a.getId(), a.getName()); } // 返回奖品名称列表 List nameList = new ArrayList<>(awardIdLsit.size()); for(Integer id : awardIdLsit){ nameList.add(awardIdNameMap.get(id)); } System.out.println(nameList);

评价

感觉非常繁琐 特别是当你习惯了Java8的函数式编程后

Guava实现

List uwList = Lists.newArrayList(new UserWinning(userId, 1), new UserWinning(userId, 2), new UserWinning(userId, 3), new UserWinning(userId, 1)); //提取奖品ID ImmutableList awardIdList = from(uwList).transform(new Function() { @Override public Integer apply(UserWinning input) { return input.getAwardId(); } }).toList(); System.out.println(awardIdList); //根据奖品ID查询奖品 List awardList = Lists.newArrayList(new Award(1, "奖品一"), new Award(2, "奖品二"), new Award(3, "奖品三")); //List --> Map 得到奖品ID和奖品Map ImmutableMap idAwardMap = uniqueIndex(awardList, new Function() { @Override public Integer apply(Award input) { return input.getId(); } }); // 返回奖品名称列表 ImmutableList awardNameList = from(awardIdList).transform(new Function() { @Override public String apply(Integer input) { return idAwardMap.get(input).getName(); } }).toList(); System.out.println(awardNameList);

评价

代码不够简洁， 看的时候还是容易被这些匿名内部类干扰，虽然写的时候也很流畅。优点是返回的集合都是不可变的。

Lambdaj实现

List uwList = Lists.newArrayList(new UserWinning(userId, 1), new UserWinning(userId, 2), new UserWinning(userId, 3), new UserWinning(userId, 1)); //提取awardIdList List awardIdList = extract(uwList, on(UserWinning.class).getAwardId()); System.out.println(awardIdList); List awardList = Lists.newArrayList(new Award(1, "奖品一"), new Award(2, "奖品二"), new Award(3, "奖品三")); //List -> Map Map idAwardMap = index(awardList, on(Award.class).getId()); //得到奖品名称列表 List nameList = convert(awardIdList, new Converter() { @Override public String convert(Integer from) { return idAwardMap.get(from).getName(); } }); System.out.println(nameList);

评价

看起来很简洁， 一目了然。但对泛型支持的不如Guava， 如List转Map代码自动生成的是Map 需要显式修改为Map。 另外也不确定相比Guava性能如何。

参考文档
https://code.google.com/archive/p/lambdaj/wikis/LambdajFeatures.wiki

因为线上使用的是Java7, 不能使用Java8的语法，故想选择一些工具类简化Java7的开发。 不确定该选用Gauva还是LambdaJ?