Recursive menu query (recursion: check yourself)

（1）level by 1 Namely 1 level ,children It is the submenu at this level

（2） Only existing data can be recursive

（3） Recursion requires an entry , That is, where to start

Concrete realization ：

（1） Recursive query ：

The complete code is as follows （ The analysis is as follows ）

 
    //======================== Recursively query all menus ===========
    // Get all menus 
    @Override
    public List<Permission> queryAllMenuGuli() {
        //1  Query all data in the menu table 
        QueryWrapper<Permission> wrapper = new QueryWrapper<>();
        wrapper.orderByDesc("id");
        List<Permission> permissionList = baseMapper.selectList(wrapper);
        //2  Query all menus list The collection is encapsulated as required 
        List<Permission> resultList = bulidPermission(permissionList);
        return resultList;
    }
 
    // Return to all menus list A method of encapsulating a collection 
    public static List<Permission> bulidPermission(List<Permission> permissionList) {
 
        // establish list aggregate , Used for data final encapsulation 
        List<Permission> finalNode = new ArrayList<>();
        // Put all the menus list A collection of traverse , Get the top menu  pid=0 menu , Set up level yes 1
        for(Permission permissionNode : permissionList) {
            // Get the top menu  pid=0 menu 
            if("0".equals(permissionNode.getPid())) {
                // Set the top-level menu level yes 1
                permissionNode.setLevel(1);
                // According to the top menu , Query the submenu , Package to finalNode Inside 
                //permissionNode This is level by 1 All data for 
                finalNode.add(selectChildren(permissionNode,permissionList));
            }
        }
        return finalNode;
    }
// This is to query the secondary and tertiary menus ：
    private static Permission selectChildren(Permission permissionNode, List<Permission> permissionList) {
        //1  Because put the second level menu in the first level menu , There are three more floors inside the second floor , Initialize the object 
        permissionNode.setChildren(new ArrayList<Permission>());
 
        //2  Traverse all menus list aggregate , Make judgments and compare , Compare id and pid Is the value the same 
        for(Permission it : permissionList) {
            // Judge  id and pid Is the value the same 
            if(permissionNode.getId().equals(it.getPid())) {
                // Put the parent menu level value +1
                int level = permissionNode.getLevel()+1;
                it.setLevel(level);
                // If children It's empty , Perform initialization operation 
                if(permissionNode.getChildren() == null) {
                    permissionNode.setChildren(new ArrayList<Permission>());
                }
                // Put the queried sub menu into the parent menu 
                permissionNode.getChildren().add(selectChildren(it,permissionList));
            }
        }
        return permissionNode;
    }

  //======================== Recursively query all menus 
     Get all the menus first , And then make a query 
    @Override
    public List<Permission> queryAllMenuGuli() {
        //1  Query all data in the menu table 
        QueryWrapper<Permission> wrapper = new QueryWrapper<>();
        wrapper.orderByDesc("id");
        List<Permission>  All contents （ Unpacked ） = baseMapper.selectList(wrapper);
        //2  Query all menus list The collection is encapsulated as required 
        List<Permission> resultList = bulidPermission( All contents （ Unpacked ）);
        return resultList;
    }

    // Return to all menus list A method of encapsulating a collection 
    public static List<Permission> bulidPermission(List<Permission> permissionList【 All contents （ Unpacked ）】) {

        // establish list aggregate , Used for data final encapsulation 
        List<Permission> finalNode 【 All contents （ Sealed ）】= new ArrayList<>();
        // Put all the menus list A collection of traverse , Get the top menu  pid=0 menu , Set up level yes 1
        for(Permission permissionNode【 First class menu 】 : permissionList) {
            // Get the top menu  pid=0 menu 
            if("0".equals(permissionNode.getPid())) {
                // Set the top-level menu level yes 1
                permissionNode.setLevel(1);
                // According to the top menu , Query the submenu , Package to finalNode Inside 
                //permissionNode This is level by 1 All data for 
                finalNode All contents （ Sealed ）.add(selectChildren（ New method ）(permissionNode【 First class menu 】,permissionList【 All contents （ Unpacked ）】));-- This is to prepare for recursion 
            }
        }
        return finalNode;
    }
// This is to query the secondary and tertiary menus ：
    private static Permission selectChildren(permissionNode【 First class menu 】,permissionList【 All contents （ Unpacked ）】) {
        //1  Because put the second level menu in the first level menu , There are three more floors inside the second floor , Initialize the object 
        permissionNode.setChildren(new ArrayList<Permission>());

        //2  Traverse all menus list aggregate , Make judgments and compare , Compare id and pid Is the value the same 
        for(Permission it【 II. Contents of the menu 】 : permissionList【 All contents （ Unpacked ）】) {
            // Judge  id and pid Is the value the same 
            if(permissionNode【 First class menu 】.getId().equals(it【 II. Contents of the menu 】.getPid())) {
                // Put the parent menu level value +1
                int level = permissionNode.getLevel()+1;
                it.setLevel(level);
                // If children It's empty , Perform initialization operation 
                if(permissionNode.getChildren() == null) {
                    permissionNode.setChildren(new ArrayList<Permission>());
                }-- Add a beautiful thing to a contrasting beautiful thing , You can do without it 
                // Put the queried sub menu into the parent menu 
                permissionNode【 First class menu 】.getChildren().add(selectChildren(it【 II. Contents of the menu 】,permissionList【 All contents （ Unpacked ）】));-- The next step is to cycle the above steps 
            }
        }
        return permissionNode【 First class menu 】;
    }