java8 stream 树_Java8新特性-使用Stream流递归实现遍历树形结构

可能平常会遇到一些需求，比如构建菜单，构建树形结构，数据库一般就使用父id来表示，为了降低数据库的查询压力，我们可以使用Java8中的Stream流一次性把数据查出来，然后通过流式处理，我们一起来看看，代码实现为了实现简单，就模拟查看数据库所有数据到List里面。

实体类：Menu.java

@Data

@Builder

public class Menu {

public Integer id;

public String name;

public Integer parentId;

public ListchildList;

public Menu(Integer id, String name, Integer parentId) {

this.id = id;

this.name = name;

this.parentId = parentId;

}

public Menu(Integer id, String name, Integer parentId, ListchildList) {

this.id = id;

this.name = name;

this.parentId = parentId;

this.childList = childList;

}

}

递归组装树形结构：

@Test

public void testtree(){

//模拟从数据库查询出来

Listmenus = Arrays.asList(

new Menu(1,"根节点",0),

new Menu(2,"子节点1",1),

new Menu(3,"子节点1.1",2),

new Menu(4,"子节点1.2",2),

new Menu(5,"根节点1.3",2),

new Menu(6,"根节点2",1),

new Menu(7,"根节点2.1",6),

new Menu(8,"根节点2.2",6),

new Menu(9,"根节点2.2.1",7),

new Menu(10,"根节点2.2.2",7),

new Menu(11,"根节点3",1),

new Menu(12,"根节点3.1",11)

);

//获取父节点

Listcollect = menus.stream().filter(m -> m.getParentId() == 0).map(

(m) -> {

m.setChildList(getChildrens(m, menus));

return m;

}

).collect(Collectors.toList());

System.out.println("-------转json输出结果-------");

System.out.println(JSON.toJSON(collect));

}

private ListgetChildrens(Menu root, Listall) {

Listchildren = all.stream().filter(m -> {

return Objects.equals(m.getParentId(), root.getId());

}).map(

(m) -> {

m.setChildList(getChildrens(m, all));

return m;

}

).collect(Collectors.toList());

return children;

}

格式化打印结果：