遞歸(心得體會)

把這種的遞歸，參數是PID

@RequestMapping(value="/queryListMenu/{pid}",method=RequestMethod.GET)
    public List<Menu> queryMenu(@PathVariable(value = "pid",required = true) String pid) {
        List<Menu> list = new ArrayList<>();
        List<Menu> listMenuParent = new ArrayList<>();
        Boolean flag = true;
        while (flag) {
            //menuParent中,沒有List<Menu>child 爲 null
            Menu menuParent = orgService.findByPid(pid);
            //如果最後一條數據爲null則把之前的數據賦給list並返回作爲最後輸出
            list = listMenuParent;
            //如果最後一條數據爲null則flag爲false,跳出if判斷
            flag = false;
            //這裏pid 是作爲child的id的
            Menu menuChild = orgService.findById(pid);
            if (menuChild != null && menuParent != null) {
                List<Menu> listChild = new ArrayList<>(1);
                /*String s = JSONObject.toJSONString(menuChild);
                Object parse = JSON.parse(s);*/
                listChild.add(menuChild);
                //一個完整的實體類對象,有List<Menu>child
                menuParent.setChild(listChild);
                //一個一個menu放入集合
                //listMenuParent.add(menuParent);
                listMenuParent.add(menuParent);

                if (StringUtils.isNotBlank(menuChild.getPid())){
                    pid = menuChild.getPid();
                    //當爲true時又返回if判斷
                    flag = true;
                }else {
                    //如果最後一條PID爲空則直接返回之前的數據
                    return listMenuParent;
                }
            }
        }
        return list;
    }

@Entity
@Table(name = "sys_menu")
public class Menu implements Serializable {

    @Id
    @Column(name = "ID")
    private String id;
    @Column(name = "NAME")
    private String name;
    @Column(name = "PID")
    private String pid;
    @Transient
    @JsonInclude(JsonInclude.Include.NON_NULL)
    private List<Menu> child;

輸出：

[
    {
        "id": "1",
            "name": "LJ",
            "pid": "2",
            "child": [
        {
            "id": "2",
                "name": "ZF",
                "pid": "3",
                "child": [
            {
                "id": "3",
                    "name": "SP",
                    "pid": "4",
                    "child": [
                {
                    "id": "4",
                        "name": "WS",
                        "pid": "5",
                        "child": [
                    {
                        "id": "5",
                            "name": "HXM",
                            "pid": "6",
                            "child": [
                        {
                            "id": "6",
                                "name": "GMY",
                                "pid": "7",
                                "child": null
                        }
                                        ]
                    }
                                ]
                }
                        ]
            }
                ]
        }
        ]
    },
    {
        "id": "2",
            "name": "ZF",
            "pid": "3",
            "child": [
        {
            "id": "3",
                "name": "SP",
                "pid": "4",
                "child": [
            {
                "id": "4",
                    "name": "WS",
                    "pid": "5",
                    "child": [
                {
                    "id": "5",
                        "name": "HXM",
                        "pid": "6",
                        "child": [
                    {
                        "id": "6",
                            "name": "GMY",
                            "pid": "7",
                            "child": null
                    }
                                ]
                }
                        ]
            }
                ]
        }
        ]
    },
    {
        "id": "3",
            "name": "SP",
            "pid": "4",
            "child": [
        {
            "id": "4",
                "name": "WS",
                "pid": "5",
                "child": [
            {
                "id": "5",
                    "name": "HXM",
                    "pid": "6",
                    "child": [
                {
                    "id": "6",
                        "name": "GMY",
                        "pid": "7",
                        "child": null
                }
                        ]
            }
                ]
        }
        ]
    },
    {
        "id": "4",
            "name": "WS",
            "pid": "5",
            "child": [
        {
            "id": "5",
                "name": "HXM",
                "pid": "6",
                "child": [
            {
                "id": "6",
                    "name": "GMY",
                    "pid": "7",
                    "child": null
            }
                ]
        }
        ]
    },
    {
        "id": "5",
            "name": "HXM",
            "pid": "6",
            "child": [
        {
            "id": "6",
                "name": "GMY",
                "pid": "7",
                "child": null
        }
        ]
    }
]

總結：不同位置(i=0,i=1等)不同引用，但是相同對象的。如果對這個對象set，那麼在不同位置都可以看到set的值

原本想得到的數據是如下這種但是發現根本不行：

[
    {
        "id": "1",
            "name": "LJ",
            "pid": "2",
            "child": [
        {
            "id": "2",
                "name": "ZF",
                "pid": "3",
                "child": null
        }]
    },
	{
        "id": "2",
            "name": "LJ",
            "pid": "3",
            "child": [
        {
            "id": "3",
                "name": "ZF",
                "pid": "4",
                "child": null
        }]
    },
	{
        "id": "4",
            "name": "LJ",
            "pid": "5",
            "child": [
        {
            "id": "5",
                "name": "ZF",
                "pid": "6",
                "child": null
        }]
    }
]

想實現上述這種格式只能：

泛型改爲Object

 private List<Object> child;

@Entity
@Table(name = "sys_menu")
public class Menu implements Serializable {

    @Id
    @Column(name = "ID")
    private String id;
    @Column(name = "NAME")
    private String name;
    @Column(name = "PID")
    private String pid;
    @Transient
    @JsonInclude(JsonInclude.Include.NON_NULL)
    private List<Object> child;

@RequestMapping(value="/queryListMenu/{pid}",method=RequestMethod.GET)
    public List<Menu> queryMenu(@PathVariable(value = "pid",required = true) String pid) {
        List<Menu> list = new ArrayList<>();
        List<Menu> listMenuParent = new ArrayList<>();
        Boolean flag = true;
        while (flag) {
            //menuParent中,沒有List<Menu>child 爲 null
            Menu menuParent = orgService.findByPid(pid);
            //如果最後一條數據爲null則把之前的數據賦給list並返回作爲最後輸出
            list = listMenuParent;
            //如果最後一條數據爲null則flag爲false,跳出if判斷
            flag = false;
            //這裏pid 是作爲child的id的
            Menu menuChild = orgService.findById(pid);
            if (menuChild != null && menuParent != null) {
                List<Object> listChild = new ArrayList<>();
                //object對象中去掉爲null的child
                String jsonMenu = JSONObject.toJSONString(menuChild);
                Object parse = JSON.parse(jsonMenu);
                listChild.add(parse);
                //一個完整的實體類對象,有List<Menu>child
                menuParent.setChild(listChild);
                //一個一個menu放入集合
                listMenuParent.add(menuParent);
                if (StringUtils.isNotBlank(menuChild.getPid())){
                    pid = menuChild.getPid();
                    //當爲true時又返回if判斷
                    flag = true;
                }else {
                   //如果最後一條PID爲空則直接返回之前的數據
                   return listMenuParent;
                }
            }

        }
        return list;
    }

注意這段代碼(看註釋理解)：

   //object對象中去掉爲null的child，目的是下一次在走到這個位置set的值不在上一次看到
   String jsonMenu = JSONObject.toJSONString(menuChild);
   Object parse = JSON.parse(jsonMenu);