Lambda表达式详解（二）
概要
本篇将通过几个案例来说明Lambda和Stream的联合使用，通过本篇你将发现使用Lambda能在一定的场景下大大的简化代码。
案例
Filter的使用
测试案例
@Before
public void init() {
log.info("begin to init data！");
ruleList = new ArrayList<>();
ruleList.add(new GoodsRule(1L, 1, 1, "3"));
ruleList.add(new GoodsRule(1L, 2, 1, "呵呵"));
ruleList.add(new GoodsRule(1L, 2, 2, "3"));
ruleList.add(new GoodsRule(1L, 3, 1, "1232"));
ruleList.add(new GoodsRule(2L, 1, 1, "3"));
ruleList.add(new GoodsRule(2L, 2, 1, "qqq"));
log.info("end to init data！");
}
@Test
public void testStreamFilter() {
log.info("过滤前:");
ruleList.forEach(rule -> log.info(gs.toJson(rule)));
log.info("过滤后:");
ruleList.stream().filter(rule -> Long.valueOf(2).equals(rule.goodsId))
.forEach(rule -> log.info(gs.toJson(rule)));
}执行结果
INFO [VIPApp] 2018-08-11 17:16:30.939 [main] com.zyxr.vip.test.mall.AdvisorTest ? - begin to init data！
INFO [VIPApp] 2018-08-11 17:16:30.940 [main] com.zyxr.vip.test.mall.AdvisorTest 260 - end to init data！
INFO [VIPApp] 2018-08-11 17:16:30.940 [main] com.zyxr.vip.test.mall.AdvisorTest 265 - 过滤前:
INFO [VIPApp] 2018-08-11 17:16:30.940 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:16:30.941 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":2,"secondType":1,"secondValue":"呵呵"}
INFO [VIPApp] 2018-08-11 17:16:30.941 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":2,"secondType":2,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:16:30.941 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":3,"secondType":1,"secondValue":"1232"}
INFO [VIPApp] 2018-08-11 17:16:30.941 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":2,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:16:30.941 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":2,"firstType":2,"secondType":1,"secondValue":"qqq"}
INFO [VIPApp] 2018-08-11 17:16:30.941 [main] com.zyxr.vip.test.mall.AdvisorTest 267 - 过滤后:
INFO [VIPApp] 2018-08-11 17:16:30.945 [main] com.zyxr.vip.test.mall.AdvisorTest 269 - {"goodsId":2,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:16:30.945 [main] com.zyxr.vip.test.mall.AdvisorTest 269 - {"goodsId":2,"firstType":2,"secondType":1,"secondValue":"qqq"}
自定义Filter
测试案例
@Test
public void testStreamFilter1() {
//goodsId为2的过滤器
Predicate goodsRulePredicate = rule -> Long.valueOf(2).equals(rule.goodsId);
//firstType为2的过滤器
Predicate fistTypePredicate = rule -> Integer.valueOf(2).equals(rule.firstType);
log.info("过滤前:");
ruleList.forEach(rule -> log.info(gs.toJson(rule)));
//过滤firstType为2的GoodsRule
log.info("过滤后:");
ruleList.stream().filter(fistTypePredicate).forEach(rule -> log.info(gs.toJson(rule)));
log.info("过滤前:");
ruleList.forEach(rule -> log.info(gs.toJson(rule)));
//过滤goodsId为2和firstType为2的GoodsRule
log.info("过滤后:");
ruleList.stream().filter(goodsRulePredicate).filter(fistTypePredicate)
.forEach(rule -> log.info(gs.toJson(rule)));
} 执行结果
INFO [VIPApp] 2018-08-11 17:19:43.758 [main] com.zyxr.vip.test.mall.AdvisorTest 252 - begin to init data！
INFO [VIPApp] 2018-08-11 17:19:43.758 [main] com.zyxr.vip.test.mall.AdvisorTest 260 - end to init data！
INFO [VIPApp] 2018-08-11 17:19:43.759 [main] com.zyxr.vip.test.mall.AdvisorTest 269 - 过滤前:
INFO [VIPApp] 2018-08-11 17:19:43.761 [main] com.zyxr.vip.test.mall.AdvisorTest 270 - {"goodsId":1,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:19:43.761 [main] com.zyxr.vip.test.mall.AdvisorTest 270 - {"goodsId":1,"firstType":2,"secondType":1,"secondValue":"呵呵"}
INFO [VIPApp] 2018-08-11 17:19:43.761 [main] com.zyxr.vip.test.mall.AdvisorTest 270 - {"goodsId":1,"firstType":2,"secondType":2,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:19:43.761 [main] com.zyxr.vip.test.mall.AdvisorTest 270 - {"goodsId":1,"firstType":3,"secondType":1,"secondValue":"1232"}
INFO [VIPApp] 2018-08-11 17:19:43.761 [main] com.zyxr.vip.test.mall.AdvisorTest 270 - {"goodsId":2,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:19:43.761 [main] com.zyxr.vip.test.mall.AdvisorTest 270 - {"goodsId":2,"firstType":2,"secondType":1,"secondValue":"qqq"}
INFO [VIPApp] 2018-08-11 17:19:43.761 [main] com.zyxr.vip.test.mall.AdvisorTest 272 - 过滤后:
INFO [VIPApp] 2018-08-11 17:19:43.764 [main] com.zyxr.vip.test.mall.AdvisorTest 273 - {"goodsId":1,"firstType":2,"secondType":1,"secondValue":"呵呵"}
INFO [VIPApp] 2018-08-11 17:19:43.764 [main] com.zyxr.vip.test.mall.AdvisorTest 273 - {"goodsId":1,"firstType":2,"secondType":2,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:19:43.764 [main] com.zyxr.vip.test.mall.AdvisorTest 273 - {"goodsId":2,"firstType":2,"secondType":1,"secondValue":"qqq"}
INFO [VIPApp] 2018-08-11 17:19:43.764 [main] com.zyxr.vip.test.mall.AdvisorTest 275 - 过滤前:
INFO [VIPApp] 2018-08-11 17:19:43.764 [main] com.zyxr.vip.test.mall.AdvisorTest 276 - {"goodsId":1,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:19:43.764 [main] com.zyxr.vip.test.mall.AdvisorTest 276 - {"goodsId":1,"firstType":2,"secondType":1,"secondValue":"呵呵"}
INFO [VIPApp] 2018-08-11 17:19:43.764 [main] com.zyxr.vip.test.mall.AdvisorTest 276 - {"goodsId":1,"firstType":2,"secondType":2,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:19:43.765 [main] com.zyxr.vip.test.mall.AdvisorTest 276 - {"goodsId":1,"firstType":3,"secondType":1,"secondValue":"1232"}
INFO [VIPApp] 2018-08-11 17:19:43.765 [main] com.zyxr.vip.test.mall.AdvisorTest 276 - {"goodsId":2,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:19:43.765 [main] com.zyxr.vip.test.mall.AdvisorTest 276 - {"goodsId":2,"firstType":2,"secondType":1,"secondValue":"qqq"}
INFO [VIPApp] 2018-08-11 17:19:43.765 [main] com.zyxr.vip.test.mall.AdvisorTest 278 - 过滤后:
INFO [VIPApp] 2018-08-11 17:19:43.765 [main] com.zyxr.vip.test.mall.AdvisorTest ? - {"goodsId":2,"firstType":2,"secondType":1,"secondValue":"qqq"}
limit使用
测试案例
@Before
public void init() {
log.info("begin to init data！");
ruleList = new ArrayList<>();
ruleList.add(new GoodsRule(1L, 1, 1, "3"));
ruleList.add(new GoodsRule(1L, 2, 1, "呵呵"));
ruleList.add(new GoodsRule(1L, 2, 2, "3"));
ruleList.add(new GoodsRule(1L, 3, 1, "1232"));
ruleList.add(new GoodsRule(2L, 1, 1, "3"));
ruleList.add(new GoodsRule(2L, 2, 1, "qqq"));
log.info("end to init data！");
}
@Test
public void testStreamLimit() {
log.info("限制前:");
ruleList.forEach(rule -> log.info(gs.toJson(rule)));
log.info("限制后:");
ruleList.stream().limit(3).forEach(rule -> log.info(gs.toJson(rule)));
}执行结果
INFO [VIPApp] 2018-08-11 17:22:47.743 [main] com.zyxr.vip.test.mall.AdvisorTest 252 - begin to init data！
INFO [VIPApp] 2018-08-11 17:22:47.743 [main] com.zyxr.vip.test.mall.AdvisorTest 260 - end to init data！
INFO [VIPApp] 2018-08-11 17:22:47.743 [main] com.zyxr.vip.test.mall.AdvisorTest 265 - 限制前:
INFO [VIPApp] 2018-08-11 17:22:47.745 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:22:47.745 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":2,"secondType":1,"secondValue":"呵呵"}
INFO [VIPApp] 2018-08-11 17:22:47.745 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":2,"secondType":2,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:22:47.745 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":3,"secondType":1,"secondValue":"1232"}
INFO [VIPApp] 2018-08-11 17:22:47.746 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":2,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:22:47.746 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":2,"firstType":2,"secondType":1,"secondValue":"qqq"}
INFO [VIPApp] 2018-08-11 17:22:47.746 [main] com.zyxr.vip.test.mall.AdvisorTest 267 - 限制后:
INFO [VIPApp] 2018-08-11 17:22:47.750 [main] com.zyxr.vip.test.mall.AdvisorTest 268 - {"goodsId":1,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:22:47.750 [main] com.zyxr.vip.test.mall.AdvisorTest 268 - {"goodsId":1,"firstType":2,"secondType":1,"secondValue":"呵呵"}
INFO [VIPApp] 2018-08-11 17:22:47.750 [main] com.zyxr.vip.test.mall.AdvisorTest 268 - {"goodsId":1,"firstType":2,"secondType":2,"secondValue":"3"}
sort使用
测试案例
@Before
public void init() {
log.info("begin to init data！");
ruleList = new ArrayList<>();
ruleList.add(new GoodsRule(1L, 1, 1, "3"));
ruleList.add(new GoodsRule(1L, 2, 1, "呵呵"));
ruleList.add(new GoodsRule(1L, 2, 2, "3"));
ruleList.add(new GoodsRule(1L, 3, 1, "1232"));
ruleList.add(new GoodsRule(2L, 1, 1, "3"));
ruleList.add(new GoodsRule(2L, 2, 1, "qqq"));
log.info("end to init data！");
}
@Test
public void testStreamSort() {
log.info("排序前:");
ruleList.forEach(rule -> log.info(gs.toJson(rule)));
//按照goodsId降序然后取前3条记录
log.info("排序后:");
ruleList.stream().sorted((GoodsRule o1, GoodsRule o2) -> (int) (o2.goodsId - o1.goodsId))
.limit(3).forEach(rule -> log.info(gs.toJson(rule)));
}执行结果
INFO [VIPApp] 2018-08-11 17:24:56.316 [main] com.zyxr.vip.test.mall.AdvisorTest 252 - begin to init data！
INFO [VIPApp] 2018-08-11 17:24:56.316 [main] com.zyxr.vip.test.mall.AdvisorTest 260 - end to init data！
INFO [VIPApp] 2018-08-11 17:24:56.316 [main] com.zyxr.vip.test.mall.AdvisorTest 265 - 排序前:
INFO [VIPApp] 2018-08-11 17:24:56.317 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:24:56.317 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":2,"secondType":1,"secondValue":"呵呵"}
INFO [VIPApp] 2018-08-11 17:24:56.317 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":2,"secondType":2,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:24:56.317 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":3,"secondType":1,"secondValue":"1232"}
INFO [VIPApp] 2018-08-11 17:24:56.317 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":2,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:24:56.318 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":2,"firstType":2,"secondType":1,"secondValue":"qqq"}
INFO [VIPApp] 2018-08-11 17:24:56.318 [main] com.zyxr.vip.test.mall.AdvisorTest 268 - 排序后:
INFO [VIPApp] 2018-08-11 17:24:56.321 [main] com.zyxr.vip.test.mall.AdvisorTest 270 - {"goodsId":2,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:24:56.321 [main] com.zyxr.vip.test.mall.AdvisorTest 270 - {"goodsId":2,"firstType":2,"secondType":1,"secondValue":"qqq"}
INFO [VIPApp] 2018-08-11 17:24:56.321 [main] com.zyxr.vip.test.mall.AdvisorTest 270 - {"goodsId":1,"firstType":1,"secondType":1,"secondValue":"3"}min和max使用
测试案例
@Before
public void init() {
log.info("begin to init data！");
ruleList = new ArrayList<>();
ruleList.add(new GoodsRule(1L, 1, 1, "3"));
ruleList.add(new GoodsRule(1L, 2, 1, "呵呵"));
ruleList.add(new GoodsRule(1L, 2, 2, "3"));
ruleList.add(new GoodsRule(1L, 3, 1, "1232"));
ruleList.add(new GoodsRule(2L, 1, 1, "3"));
ruleList.add(new GoodsRule(2L, 2, 1, "qqq"));
log.info("end to init data！");
}
@Test
public void testStreamMinAndMax() {
ruleList.forEach(rule -> log.info(gs.toJson(rule)));
//按照goodsId降序然后取前3条记录
GoodsRule minRule = ruleList.stream().min((GoodsRule o1, GoodsRule o2) -> (int) (o2.goodsId - o1.goodsId)).get();
log.info("minRule is :{}",gs.toJson(minRule));
GoodsRule maxRule = ruleList.stream().max((GoodsRule o1, GoodsRule o2) -> (int) (o2.goodsId - o1.goodsId)).get();
log.info("maxRule is :{}",gs.toJson(maxRule));
}执行结果
INFO [VIPApp] 2018-08-11 17:26:59.922 [main] com.zyxr.vip.test.mall.AdvisorTest 252 - begin to init data！
INFO [VIPApp] 2018-08-11 17:26:59.922 [main] com.zyxr.vip.test.mall.AdvisorTest ? - end to init data！
INFO [VIPApp] 2018-08-11 17:26:59.923 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:26:59.923 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":2,"secondType":1,"secondValue":"呵呵"}
INFO [VIPApp] 2018-08-11 17:26:59.923 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":2,"secondType":2,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:26:59.923 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":1,"firstType":3,"secondType":1,"secondValue":"1232"}
INFO [VIPApp] 2018-08-11 17:26:59.923 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":2,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:26:59.924 [main] com.zyxr.vip.test.mall.AdvisorTest 266 - {"goodsId":2,"firstType":2,"secondType":1,"secondValue":"qqq"}
INFO [VIPApp] 2018-08-11 17:26:59.928 [main] com.zyxr.vip.test.mall.AdvisorTest 269 - minRule is :{"goodsId":2,"firstType":1,"secondType":1,"secondValue":"3"}
INFO [VIPApp] 2018-08-11 17:26:59.930 [main] com.zyxr.vip.test.mall.AdvisorTest 271 - maxRule is :{"goodsId":1,"firstType":1,"secondType":1,"secondValue":"3"}
并行的stream
测试案例
@Before
public void init() {
log.info("begin to init data！");
ruleList = new ArrayList<>();
ruleList.add(new GoodsRule(1L, 1, 1, "3"));
ruleList.add(new GoodsRule(1L, 2, 1, "呵呵"));
ruleList.add(new GoodsRule(1L, 2, 2, "3"));
ruleList.add(new GoodsRule(1L, 3, 1, "1232"));
ruleList.add(new GoodsRule(2L, 1, 1, "3"));
ruleList.add(new GoodsRule(2L, 2, 1, "qqq"));
log.info("end to init data！");
}
@Test
public void testParallelStream() {
LongSummaryStatistics longSummaryStatistics = ruleList.parallelStream().mapToLong(x -> x.goodsId)
.summaryStatistics();
log.info("ruleList中最大的goodsId：{}",longSummaryStatistics.getMax());
log.info("ruleList中最小的goodsId：{}",longSummaryStatistics.getMin());
log.info("ruleList中goodsId总和为：{}",longSummaryStatistics.getSum());
log.info("ruleList中记录数为：{}",longSummaryStatistics.getCount());
log.info("ruleList中goodsId的平均值为：{}",longSummaryStatistics.getAverage());
}执行结果
INFO [VIPApp] 2018-08-11 17:28:51.940 [main] com.zyxr.vip.test.mall.AdvisorTest ? - begin to init data！
INFO [VIPApp] 2018-08-11 17:28:51.941 [main] com.zyxr.vip.test.mall.AdvisorTest 260 - end to init data！
INFO [VIPApp] 2018-08-11 17:28:51.953 [main] com.zyxr.vip.test.mall.AdvisorTest ? - ruleList中最大的goodsId：2
INFO [VIPApp] 2018-08-11 17:28:51.953 [main] com.zyxr.vip.test.mall.AdvisorTest 269 - ruleList中最小的goodsId：1
INFO [VIPApp] 2018-08-11 17:28:51.953 [main] com.zyxr.vip.test.mall.AdvisorTest 270 - ruleList中goodsId总和为：8
INFO [VIPApp] 2018-08-11 17:28:51.953 [main] com.zyxr.vip.test.mall.AdvisorTest 271 - ruleList中记录数为：6
INFO [VIPApp] 2018-08-11 17:28:51.953 [main] com.zyxr.vip.test.mall.AdvisorTest 272 - ruleList中goodsId的平均值为：1.3333333333333333
总结
通过Lambda表达式和集合Stream的使用案例来看，在集合操作场景，也许能给广大程序员提供一种新的解决思路。