這個原理是 一次性把數據庫所有分類讀取出來之後再根據pid來排序。

比較簡單，好理解。

public static List<Category> cates;
private static List<Category> tmpCates = new ArrayList<Category>();

public static void main(String[] args) {

    init();
    List<Category> cList = tree( cates , 0 , 0 );
    for (Category c:cList) {
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < c.getLevel(); i++){
            sb.append("--");
        }
        System.out.println( sb.toString() + c.getName() );
    }

}

public static List<Category> tree( List<Category> cs , Integer pid , Integer level ){


    for (Category c: cs) {
        if( c.getParent_id() == pid ){
            c.setLevel( level );
            tmpCates.add(c);
            tree( cs , c.getId() , level+1 );
        }
    }
    return tmpCates;
}

public static void init(){
    cates = new ArrayList<Category>();
    Category c1 = new Category();
    c1.setId(1);
    c1.setName("廣東");
    c1.setParent_id(0);
    cates.add(c1);

    c1 = new Category();
    c1.setId(2);
    c1.setName("陜西");
    c1.setParent_id(0);
    cates.add(c1);

    c1 = new Category();
    c1.setId(3);
    c1.setName("四川");
    c1.setParent_id(0);
    cates.add(c1);

    c1 = new Category();
    c1.setId(5);
    c1.setName("深圳");
    c1.setParent_id(1);
    cates.add(c1);

    c1 = new Category();
    c1.setId(6);
    c1.setName("陜西");
    c1.setParent_id(2);
    cates.add(c1);

    c1 = new Category();
    c1.setId(8);
    c1.setName("成都");
    c1.setParent_id(3);
    cates.add(c1);

    c1 = new Category();
    c1.setId(9);
    c1.setName("寶雞");
    c1.setParent_id(2);
    cates.add(c1);


}

這個主要的方法就是tree()函數

java簡單的無限極分類