stream() 对象集合取出一个字段成新集合
1、
// 采集门店属性项
List<CollectionShopAttr> shopAttrList = collectionShopService .listShopAttrByShopId(collectShopDetailReq.getId());
对象集合取出一个字段成新集合
//取出采集项attrKey为集合
List<String> attrKeyList = shopAttrList.stream().map(CollectionShopAttr::getAttrKey).collect(Collectors.toList());
2、
List<CollectionTemplateContent> contentList = collectionTemplateService .listContentByTemplateIdAndType(detail.getType(), detail.getMerchantId());
List<String> tempKeyList = contentList.stream().map(CollectionTemplateContent::getCode).collect(Collectors.toList());
IO流用于读写，Stream流用于处理数组和集合数据，解决传统集合遍历。filter()方法用于过滤，forEach+sout循环输出结果。
@Test public void streamTest() { /** * IO流用于读写，Stream流用于处理数组和集合数据，解决传统集合遍历 */ Set<String> set = new TreeSet<>(); set.add("张**"); set.add("wang**"); set.add("张*1"); set.add("张wagn**"); set.add("kak**"); set.add("lili**"); set.add("张**"); //forEach set.stream().filter(name -> name.startsWith("张")) .filter(name -> name.length() == 3) .forEach(name -> System.out.println(name)); }
初始化组装map，map输出，用keySet方法获得key集合。
@Data class Entity { Integer id; String username; } @Test public void keySetTest() { /** * keySet */ //初始化list List<Entity> list = new LinkedList<>(); for (int i = 0; i < 10; i++) { Entity object = new Entity(); object.setId(i); object.setUsername(String.valueOf(i >>> 1)); log.info("i:{}, i >>> 1:{}", i, i >>> 1); list.add(object); } //初始化map Map<Integer, String> map = new TreeMap<>(); if (CollectionUtil.isNotEmpty(list)) { map = list.stream().collect(Collectors.toMap(Entity::getId, Entity::getUsername, (t1, t2) -> t2)); log.info("map:{}", map); } //map输出 if (null != map) { Map<Integer, String> finalMap = map; map.keySet().forEach(item -> { System.out.println("key = " + item + ", value = " + finalMap.get(item)); }); Set<Integer> set = map.keySet(); System.out.println(set); } }
以上两个输出结果
"C:\Program Files\Java\jdk1.8.0_131\bin\java" -ea -Didea.test.cyclic.buffer.size=1048576 "-javaagent:E:\software\IntelliJ IDEA 2017.2.5\lib\idea_rt.jar=62217:E:\software\IntelliJ IDEA 2017.2.5\bin" -Dfile.encoding=UTF-8 -classpath "E:\software\IntelliJ IDEA 2017.2.5\lib\idea_rt.jar;E:\software\IntelliJ IDEA 2017.2.5\plugins\junit\lib\junit-rt.jar;E:\software\IntelliJ IDEA 2017.2.5\plugins\junit\lib\junit5-rt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\nashorn.jar;C:\Program 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-netflix-archaius-2.2.2.RELEASE.jar;D:\maven\repository\org\springframework\boot\spring-boot-starter-aop\2.2.6.RELEASE\spring-boot-starter-aop-2.2.6.RELEASE.jar;D:\maven\repository\org\springframework\spring-aop\5.2.5.RELEASE\spring-aop-5.2.5.RELEASE.jar;D:\maven\repository\org\aspectj\aspectjweaver\1.9.5\aspectjweaver-1.9.5.jar;D:\maven\repository\io\github\openfeign\form\feign-form-spring\3.8.0\feign-form-spring-3.8.0.jar;D:\maven\repository\io\github\openfeign\form\feign-form\3.8.0\feign-form-3.8.0.jar;D:\maven\repository\commons-fileupload\commons-fileupload\1.4\commons-fileupload-1.4.jar;D:\maven\repository\org\springframework\boot\spring-boot-starter-actuator\2.2.6.RELEASE\spring-boot-starter-actuator-2.2.6.RELEASE.jar;D:\maven\repository\org\springframework\boot\spring-boot-actuator-autoconfigure\2.2.6.RELEASE\spring-boot-actuator-autoconfigure-2.2.6.RELEASE.jar;D:\maven\repository\org\springframework\boot\spring-boot-actuator\2.2.6.RELEASE\spring-boot-actuator-2.2.6.RELEASE.jar;D:\maven\repository\com\fasterxml\jackson\datatype\jackson-datatype-jsr310\2.10.3\jackson-datatype-jsr310-2.10.3.jar;D:\maven\repository\io\micrometer\micrometer-core\1.3.6\micrometer-core-1.3.6.jar;D:\maven\repository\org\hdrhistogram\HdrHistogram\2.1.11\HdrHistogram-2.1.11.jar;D:\maven\repository\org\latencyutils\LatencyUtils\2.0.3\LatencyUtils-2.0.3.jar;D:\maven\repository\com\hankcs\hanlp\portable-1.7.8\hanlp-portable-1.7.8.jar;D:\maven\repository\org\projectlombok\lombok\1.18.12\lombok-1.18.12.jar;D:\maven\repository\com\lego\lego-merchant-api\1.0.2-SNAPSHOT\lego-merchant-api-1.0.2-SNAPSHOT.jar;D:\maven\repository\com\lego\lego-data-api\1.4.2-SNAPSHOT\lego-data-api-1.4.2-20211221.102338-439.jar;D:\maven\repository\com\lego\saas-brand-api\1.0.0-SNAPSHOT\saas-brand-api-1.0.0-20220111.074747-39.jar;D:\maven\repository\com\lego\saas-report-api\1.0.0-SNAPSHOT\saas-report-api-1.0.0-SNAPSHOT.jar;D:\maven\repository\com\fuxiplus\fuxi-plus-shopmall-api\1.0.1-SNAPSHOT\fuxi-plus-shopmall-api-1.0.1-20220112.075826-28.jar;D:\maven\repository\com\fuxiplus\fuxi-plus-model-api\1.0.3-SNAPSHOT\fuxi-plus-model-api-1.0.3-20220112.080654-5.jar;D:\maven\repository\com\fuxiplus\fuxi-plus-bgm-editor-annotation\1.0.3-SNAPSHOT\fuxi-plus-bgm-editor-annotation-1.0.3-20220112.080643-4.jar;D:\maven\repository\com\fuxiplus\fuxi-plus-brand-api\1.0.0-SNAPSHOT\fuxi-plus-brand-api-1.0.0-20220111.090602-15.jar;D:\maven\repository\com\fuxiplus\fuxi-plus-common-core\1.0.2\fuxi-plus-common-core-1.0.2.jar;D:\maven\repository\com\fuxiplus\fuxi-plus-common-swagger\1.0.1\fuxi-plus-common-swagger-1.0.1.jar;D:\maven\repository\org\springframework\cloud\spring-cloud-starter-openfeign\2.2.2.RELEASE\spring-cloud-starter-openfeign-2.2.2.RELEASE.jar;D:\maven\repository\io\github\openfeign\feign-core\10.7.4\feign-core-10.7.4.jar;D:\maven\repository\io\github\openfeign\feign-slf4j\10.7.4\feign-slf4j-10.7.4.jar;D:\maven\repository\io\github\openfeign\feign-hystrix\10.7.4\feign-hystrix-10.7.4.jar;E:\software\IntelliJ IDEA 2017.2.5\plugins\junit\lib\junit-platform-launcher-1.0.0.jar" com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 -junit5 @w@C:\Users\SW00550\AppData\Local\Temp\idea_working_dirs_junit.tmp @C:\Users\SW00550\AppData\Local\Temp\idea_junit.tmp -socket62216 19:45:35.563 [main] INFO com.collect.server.service.test2 - i:0, i >>> 1:0 19:45:35.577 [main] INFO com.collect.server.service.test2 - i:1, i >>> 1:0 19:45:35.577 [main] INFO com.collect.server.service.test2 - i:2, i >>> 1:1 19:45:35.577 [main] INFO com.collect.server.service.test2 - i:3, i >>> 1:1 19:45:35.577 [main] INFO com.collect.server.service.test2 - i:4, i >>> 1:2 19:45:35.577 [main] INFO com.collect.server.service.test2 - i:5, i >>> 1:2 19:45:35.577 [main] INFO com.collect.server.service.test2 - i:6, i >>> 1:3 19:45:35.577 [main] INFO com.collect.server.service.test2 - i:7, i >>> 1:3 19:45:35.587 [main] INFO com.collect.server.service.test2 - i:8, i >>> 1:4 19:45:35.587 [main] INFO com.collect.server.service.test2 - i:9, i >>> 1:4 19:45:35.599 [main] INFO com.collect.server.service.test2 - map:{0=0, 1=0, 2=1, 3=1, 4=2, 5=2, 6=3, 7=3, 8=4, 9=4} key = 0, value = 0 key = 1, value = 0 key = 2, value = 1 key = 3, value = 1 key = 4, value = 2 key = 5, value = 2 key = 6, value = 3 key = 7, value = 3 key = 8, value = 4 key = 9, value = 4 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 张** 张*1 Process finished with exit code 0
延迟方法：支持链式调用；终结方法：count和forEach方法
@Slf4j public class test2 { /** * 延迟方法：支持链式调用 * 终结方法：count和forEach方法 */ @Test public void test2() { Stream<String> stream = Stream.of("zhansan", "lisi", "zhaoliu"); stream.forEach(name -> System.out.println(name)); /** * output * zhansan lisi zhaoliu */ } @Test public void test3() { Stream<String> stream = Stream.of("zhansan", "lisi", "zhaoliu"); Stream<String> stream2 = stream.filter((String name) -> {return name.startsWith("zhan");}); stream2.forEach(name -> System.out.println(name)); /** * output * zhansan */ } @Test public void test4() { Stream<String> stream = Stream.of("1", "2", "3", "4"); Stream<Integer> stream2 = stream.map((String s) -> { return Integer.parseInt(s); }); stream2.forEach(i -> System.out.print(i + " ")); /** * output: * 1 2 3 4 */ } @Test public void test5() { Stream<String> stream = Stream.of("1", "2", "3", "22"); //count long count = stream.count(); System.out.println(count); /** * output:4 */ } @Test public void test6() { String[] arr = {"djkklsdfjklf", "dfsjkksdf", "djksfksdjkfk", "dfsdf", "sfsdfsd", "d", "dd"}; Stream<String> stream = Stream.of(arr); //只要前三个元素 Stream<String> stream2 = stream.limit(3); stream2.forEach(name -> System.out.println(name)); /** * output * djkklsdfjklf dfsjkksdf djksfksdjkfk */ } @Test public void test7() { String[] arr = {"djkklsdfjklf", "dfsjkksdf", "djksfksdjkfk", "dfsdf", "sfsdfsd", "d", "dd"}; Stream<String> stream = Stream.of(arr); //只要跳过三个元素 Stream<String> stream2 = stream.skip(3); stream2.forEach(name -> System.out.println(name)); /** * output * dfsdf sfsdfsd d dd */ } @Test public void test8() { Stream<String> stream1 = Stream.of("dfssdfsdf", "33333", "3354555"); String[] arr = {"djkklsdfjklf", "dfsjkksdf", "djksfksdjkfk", "dfsdf", "sfsdfsd", "d", "dd"}; Stream<String> stream = Stream.of(arr); //合并 Stream<String> concat = Stream.concat(stream1, stream); concat.forEach(name -> System.out.println(name)); /** * output * dfssdfsdf 33333 3354555 djkklsdfjklf dfsjkksdf djksfksdjkfk dfsdf sfsdfsd d dd */ } }
集合元素处理实例
public class test2 { @Test public void test8() { ArrayList<String> two = new ArrayList<>(); two.add("ddf"); two.add("ddfg"); two.add("djkkdfjk"); two.add("ddf"); two.add("ddfg"); two.add("djkkdfjk"); Stream<String> stream1 = two.stream().filter(name -> name.startsWith("dd")).skip(2); Stream<String> stream2 = two.stream().filter(name -> name.length() == 3).limit(3); Stream.concat(stream1, stream2).map(name -> new Person(name)).forEach(p -> System.out.println(p.toString())); } class Person { private String name; public Person(String name) { this.name = name; } } }
stream倒序
records = records.stream().sorted(Comparator.comparing(SurveyShopPageResp::getGmtCreate) .reversed()).collect(Collectors.toList());
