【项目】Java树形结构集合分页，java对list集合进行分页

需求

商品类目树数据量大导致加载太慢，需添加一个分页功能。

难点

• 树状结构不能用mybatis-plus自带的分页功能，需自己写分页逻辑
• 因数据量大，需进行缓存处理

实现

第一步：查出所有树形集合数据 （需进行缓存处理）

List<GoodsCategoryTree> resultList = goodsCategoryService.selectTree(null);

    List<GoodsCategoryTree> selectTree(GoodsCategory goodsCategory);

selectTree 方法步骤：

判断key是否存在，如果存在，直接取缓存的值 ，不存在就从数据库查出数据，并把值存到redis里。

    @Overridepublic List<GoodsCategoryTree> selectTree(GoodsCategory goodsCategory) {if(redisTemplate.hasKey(CacheConstants.GOODS_CATEGORY_TREE_KEY)){log.info("商品类目管理 selectTree cache");List<GoodsCategoryTree> cacheList = SpringUtils.getBean(RedisCache.class).getCacheList(CacheConstants.GOODS_CATEGORY_TREE_KEY);return cacheList;}log.info("商品类目管理 selectTree db");List<GoodsCategoryTree> treeList = getTree(this.list(Wrappers.lambdaQuery(goodsCategory)));if (CollUtil.isNotEmpty(treeList)){SpringUtils.getBean(RedisCache.class).setCacheList(CacheConstants.GOODS_CATEGORY_TREE_KEY,treeList);}return treeList;}

其中 getTree()如下：

	/*** @Description: 构建树*/private List<GoodsCategoryTree> getTree(List<GoodsCategory> entitys) {List<GoodsCategoryTree> treeList = entitys.stream().filter(entity -> !entity.getId().equals(entity.getParentId())).sorted(Comparator.comparingInt(GoodsCategory::getSort)).map(entity -> {GoodsCategoryTree node = new GoodsCategoryTree();BeanUtil.copyProperties(entity, node);return node;}).collect(Collectors.toList());return TreeUtil.build(treeList, CommonConstants.PARENT_ID);}

TreeUtil类：

@UtilityClass
public class TreeUtil {/*** 两层循环实现建树** @param treeNodes 传入的树节点列表* @return*/public <T extends TreeNode> List<T> build(List<T> treeNodes, Object root) {List<T> trees = new ArrayList<>();for (T treeNode : treeNodes) {if (root.equals(treeNode.getParentId())) {trees.add(treeNode);
//				trees.sort(Comparator.comparing(TreeNode::getSort));}for (T it : treeNodes) {if (it.getParentId().equals(treeNode.getId())) {treeNode.addChildren(it);
//					treeNode.getChildren().sort(Comparator.comparing(TreeNode::getSort));}}}return trees;}
}

第二步：分页 GoodsCategoryController

	/*** 返回树形集合分页数据** @return*/@ApiOperation(value = "返回树形集合分页数据")@GetMapping("/treePage")public R getGoodsCategoryTree(Page page, GoodsCategory goodsCategory) {//得到所有数据List<GoodsCategoryTree> resultList = goodsCategoryService.selectTree(null);if (resultList != null && resultList.size() > 0) {page.setTotal(resultList.size());}//分页List<GoodsCategoryTree> finalList =  goodsCategoryService.getFinalListByPage(page,resultList);if (finalList != null && finalList.size() > 0) {page.setRecords(finalList);}return R.ok(page);}

分页

	/** 分页查询类目树*/List<GoodsCategoryTree> getFinalListByPage(Page page , List<GoodsCategoryTree> resultList );

getGoodsCategoryTree方法步骤：

参考：java对list集合进行分页
首先把数据根据创建时间倒序排列，再进行分页

	@Overridepublic List<GoodsCategoryTree> getFinalListByPage(Page page, List<GoodsCategoryTree> resultList) {//根据创建时间倒序排列List<GoodsCategoryTree> treeList = resultList.stream().sorted(Comparator.comparing(GoodsCategoryTree::getCreateTime).reversed()).collect(Collectors.toList());//进行分页List<GoodsCategoryTree> subList = treeList.stream().skip((page.getCurrent()-1)*page.getSize()).limit(page.getSize()).collect(Collectors.toList());return subList;}

第三步：前端实现

avue-crud 组件加上:page.sync=“page”

      <avue-crudref="crud":data="tableData":page.sync="page":permission="permissionList":table-loading="tableLoading":option="tableOption":before-open="beforeOpen"v-model="form"@on-load="getPage"@refresh-change="refreshChange"@row-update="handleUpdate"@row-save="handleSave"@row-del="handleDel">

data() 加上：

      page: {total: 0, // 总页数currentPage: 1, // 当前页数pageSize: 20, // 每页显示多少条ascs: [], //升序字段descs: "create_time", //降序字段},paramsSearch: {},date: [],};

重写getPage()方法：

getPage(page, params) {this.tableLoading = true;fetchTree(Object.assign({current: page.currentPage,size: page.pageSize,descs: this.page.descs,ascs: this.page.ascs,beginTime: this.date[0],endTime: this.date[1],},params,this.paramsSearch)).then((response) => {let tableData = response.data.data.records;this.tableData = tableData;this.page.total = response.data.data.total;this.page.currentPage = page.currentPage;this.page.pageSize = page.pageSize;let parentIdDIC = [{id: "0",name: "顶级分类",parentId: "0",},];tableData.forEach((item) => {parentIdDIC.push({id: item.id,name: item.name,parentId: item.parentId,});});this.$refs.crud.DIC.parentId = parentIdDIC;this.tableLoading = false;}).catch(() => {this.tableLoading = false;});},

效果图：