简单list转化为tree结构

 1     @Override
     public List<Module> getTree() {
         List<Module> list = moduleMapper.queryList();
         // List<Module> modules = makeTree(list);
         return list;
     }

     private List<Module> makeTree(List<Module> list) {
         List<Module> parent = new ArrayList<Module>();
         // get parentId = null;
         for (Module e : list) {
             if (e.getParent_Module() == null) {
                 e.setChildren(new ArrayList<Module>(0));
                 parent.add(e);
             }
         }
         // 删除parentId = null;
         list.removeAll(parent);

         makeChildren(parent, list);

         return parent;
     }

     private void makeChildren(List<Module> parent, List<Module> children) {
         if (children.isEmpty()) {
             return;
         }

         List<Module> tmp = new ArrayList<Module>();
         for (Module c1 : parent) {
             for (Module c2 : children) {
                 c2.setChildren(new ArrayList<Module>(0));
                 if (c1.getId().equals(c2.getParent_Module().getId())) {
                     c1.getChildren().add(c2);
                     tmp.add(c2);
                 }
             }
         }

         children.removeAll(tmp);

         makeChildren(tmp, children);
     }

补充po类：

package com.zktx.platform.entity.tb;

import java.util.ArrayList;
import java.util.List;

public class Module {
	private Integer id;
	private String class_name;
	private String description;
	private String name;
	private Integer priority;
	private String sn;
	private String url;
	private Integer parent_id;
	private Module parent_Module;
	private List<Module> children = new ArrayList<Module>();

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getClass_name() {
		return class_name;
	}

	public void setClass_name(String class_name) {
		this.class_name = class_name;
	}

	public String getDescription() {
		return description;
	}

	public void setDescription(String description) {
		this.description = description;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Integer getPriority() {
		return priority;
	}

	public void setPriority(Integer priority) {
		this.priority = priority;
	}

	public String getSn() {
		return sn;
	}

	public void setSn(String sn) {
		this.sn = sn;
	}

	public String getUrl() {
		return url;
	}

	public void setUrl(String url) {
		this.url = url;
	}

	public Integer getParent_id() {
		return parent_id;
	}

	public void setParent_id(Integer parent_id) {
		this.parent_id = parent_id;
	}

	public Module getParent_Module() {
		return parent_Module;
	}

	public void setParent_Module(Module parent_Module) {
		this.parent_Module = parent_Module;
	}

	public List<Module> getChildren() {
		return children;
	}

	public void setChildren(List<Module> children) {
		this.children = children;
	}

}