Java 类型转换

引用对象数组类型转换

• String数组转Integer数组

 String[] strIds = new String[]{"123","321","567"};
 Integer[] ids = (Integer[]) ConvertUtils.convert(strIds, Integer.class);

 Double[] ids = (Double[]) ConvertUtils.convert(strIds, Double.class);
 Long[] ids = (Long[]) ConvertUtils.convert(strIds, Long.class);

注：支持数组与数组之间的直接转换，如String->Long String->Double

数组与List转换

 public class User{
     private Long id;
     private String name;
     //省略get,set....
 }
 
String[] arrays = {"a", "b", "c"};

//数组转List
List<String> list = Stream.of(arrays).collect(Collectors.toList());
//List转数组
String[] strings = list.stream().toArray(String[]::new);
//对象取值
String[] strings = list.stream().map(User::getName).toArray();
//对象取值，转型
String[] ids =  (String[])ConvertUtils.convert(list.stream().map(User::getId).toArray(), String.class);

引用对象转值

• Long数组转long数组

 Long[] longIds = new Long[]{123123L,321321L,56786L};
 long[] ids = Arrays.stream(longIds).filter(Objects::nonNull).distinct().mapToLong(Long::longValue).toArray();

 //String[] strIds = new String[]{"123","321","567"};
 //long[] ids = Arrays.stream(strIds).filter(Objects::nonNull).distinct().mapToLong(Long::parseLong).toArray();

List转Map

 public class User{
     private Long id;
     private String name;
     //省略get,set....
 }
 
 //不能重复Key,值不能为空
 Map<Long, String> map = list.stream().collect(Collectors.toMap(User::getId, User::getName));
 //重载，不能重复Key,值可以为空
 Map<Long, String> map = list.stream().collect(HashMap::new, (m,v)->m.put(v.getId(), v.getName()),HashMap::putAll);
 //去重复取新值 Map值不能为空
 Map<Long, String> map = list.stream().collect(Collectors.toMap(User::getId, User::getName,(oldValue,newValue)->newValue)));
 //获取对象   Map值不能为空
 Map<Long, User> map = list.stream().collect(Collectors.toMap(User::getId,Function.identity(),(oldValue,newValue)->newValue)));
 //去重复取新值  过滤空
 Map<Long, String> map = list.stream()
          .filter(user->user.getId()!=null)
          .filter(user->user.getName()!=null)
          .collect(Collectors.toMap(User::getId, User::getName,(oldValue,newValue)->newValue)));

Map转List

 public class User{
     private Long id;
     private String name;
     //省略get,set....
 }
 
 //获取值
 List<User> userList = new ArrayList<>(userMap.values());
 //获取键
 List<Long> ids = new ArrayList(userMap.keySet());
 //获取子元素
 List<String> names =  userMap.values().stream().collect(ArrayList::new,(m,v)->m.add(v.getName()),ArrayList::addAll);
//获取子元素 + 过滤
 List<String> names =  userMap.values().stream()
          .filter(user->!user.getName().equals("admin"))
          .collect(ArrayList::new,(m,v)->m.add(v.getName()),ArrayList::addAll);