public class Comment {

    /**
     * id
     */
    private Integer id;

    /**
     * 父類id
     */
    private Integer parentId;

    /**
     * 消息
     */
    private String message;
}

查詢到所有的評論數據。方便展示樹形數據，對Comment添加回復列表

List<ViewComment> children

ViewComment結構如下：

// 展示樹形數據
public class ViewComment {
    /**
     * id
     */
    private Integer id;
    /**
     * 父類id
     */
    private Integer parentId;
    /**
     * 消息
     */
    private String message;
    /**
     * 回復列表
     */
    private List<ViewComment> children = new ArrayList<>();
}

添加非回復評論

非回復評論的parent_id為-1，先找到非回復評論：

List<ViewComment> viewCommentList = new ArrayList<>();
// 添加模擬數據
Comment comment1 = new Comment(1,-1,"留言1");
Comment comment2 = new Comment(2,-1,"留言2");
Comment comment3 = new Comment(3,1,"留言3，回復留言1");
Comment comment4 = new Comment(4,1,"留言4，回復留言1");
Comment comment5 = new Comment(5,2,"留言5，回復留言2");
Comment comment6 = new Comment(6,3,"留言6，回復留言3");
//添加非回復評論
for (Comment comment : commentList) {
    if (comment.getParentId() == -1) {
        ViewComment viewComment = new ViewComment();
        BeanUtils.copyProperties(comment,viewComment);
        viewCommentList.add(viewComment);
    }
}

遞歸添加回復評論

遍歷每條非回復評論，遞歸添加回復評論：

for(ViewComment viewComment : viewCommentList) {
    add(viewComment,commentList);
}
private void add(ViewComment rootViewComment, List<Comment> commentList) {
    for (Comment comment : commentList) {
        // 找到匹配的 parentId  
        if (rootViewComment.getId().equals(comment.getParentId())) {
            ViewComment viewComment = new ViewComment();
            BeanUtils.copyProperties(comment,viewComment);
            rootViewComment.getChildren().add(viewComment);
            //遞歸調用 
            add(viewComment,commentList);
        }
    }
}