list.stream().map().collect(Collectors.toList())

java api 特性 stream只能被“消费”一次，一旦遍历过就会失效，就像容器的迭代器那样，想要再次遍历必须重新生成 map():用于映射每个元素到对应的结果。 filter():filter 方法用于通过设置的条件过滤出元素。 Collectors.toList() 用来结束Stream流 例如： //userList User实体类对象集合 //User 实体类 //getId 实体类属性的get方法 List<int> ids= userList.stream().map(User::getId).collect(Collectors.toList()) //或者 把数据放到map根据user.getId(条件) 循环 在转换成list List<int> ids= userList.stream().map(user->user.getId()).collect(Collectors.toList());

//过滤list集合中属性type为1的值并赋值给permissions集合 在返回list集合 .collect(Collectors.toList()) 转换成list集合 List<Permission> permissions = list.stream().filter(l -> l.getType().equals(1)) .collect(Collectors.toList());

list转map

Map<String,Entity> statMap = statList.stream().collect(Collectors.toMap(Entity::getId, Entity -> Entity)); List<String> collect = roleResultList.stream().map(AcAppRole::getName).collect(Collectors.toList()); Map<Integer, String> map = new HashMap<>(); map.put(10, "apple"); map.put(20, "orange"); map.put(30, "banana"); map.put(40, "watermelon"); map.put(50, "dragonfruit"); System.out.println(" 1. Export Map Key to List..."); List<Integer> result = map.keySet().stream().collect(Collectors.toList()); result.forEach(System.out::println); System.out.println(" 2. Export Map Value to List..."); List<String> result2 = map.values().stream().collect(Collectors.toList()); result2.forEach(System.out::println); System.out.println(" 3. Export Map Value to List..., say no to banana"); List<String> result3 = map.keySet().stream().filter(x -> !"banana".equalsIgnoreCase(x)).collect(Collectors.toList()); result3.forEach(System.out::println); List<String> resultValues = map.entrySet().stream().sorted(Map.Entry.<Integer, String>comparingByKey().reversed()) .peek(e -> resultSortedKey.add(e.getKey())) .map(x -> x.getValue()) .filter(x -> !"banana".equalsIgnoreCase(x)) .collect(Collectors.toList()); public static void main(String args[]) { SqlServerReader tester = new SqlServerReader(); tester.testCaseFormat(); } private void testCaseFormat() { System.out.println(CaseFormat.LOWER_HYPHEN.to(CaseFormat.LOWER_CAMEL, "test-data")); System.out.println(CaseFormat.LOWER_UNDERSCORE.to(CaseFormat.LOWER_CAMEL, "test_data")); System.out.println(CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.UPPER_CAMEL, "test_data")); System.out.println(CaseFormat.LOWER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, "testdata")); System.out.println(); System.out.println(CaseFormat.LOWER_CAMEL.to(CaseFormat.LOWER_HYPHEN, "testData")); }

list转逗号分隔的字符串CollectionUtil.join

List<SysRole> roleList = sysRoleService.list(roleWrapper);
List<String> roleIdList = roleList.stream().map(SysRole::getId).collect(Collectors.toList());
List<String> roleNames = roleList.stream().map(SysRole::getRoleName).collect(Collectors.toList());
sysUser.setUserRoleNames(CollectionUtil.join(roleNames, ","));

字符串转list

List<Long> shipIdList = Arrays.stream(shipIds.split(",")).map(Long::parseLong).collect(Collectors.toList());

list根据某个对象属性去重

// 根据name去重 List<Person> unique = persons.stream().collect( Collectors.collectingAndThen( Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(Person::getName))), ArrayList::new) );

// 根据name,sex两个属性去重 List<Person> unique = persons.stream().collect( Collectors. collectingAndThen( Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(o -> o.getName() + ";" + o.getSex()))), ArrayList::new) );

List<Person> filterList = persons.stream().filter(p -> p.getSex().equals(1)).collect(Collectors.toList());