背景

公司的中台产品，需要对外部API接口返回的JSON数据进行采集入湖，有时候外部API接口返回的JSON数据层级嵌套比较深，举个栗子:

 上述的JSON数据中，最外层为请求返回对象，data里面包含返回的业务数据，业务数据按照学校 / 班级 / 学生进行嵌套

在数据入湖时，需要按照最内层的学生视角将数据拆分为行列数据，最终的拆分结果如下:

由于对接的外部API接口返回的JSON数据结构不是统一的、固定的，所以需要通过一种算法对每一层对象、数组进行遍历和钻取，实现JSON数据的扁平化

网上找了一些JSON扁平化的中间件，例如：Json2Flat在扁平化处理过程不太完美，不支持跨层级的数组嵌套结构

所以决定自己实现扁平化处理

关键代码如下:

public class LinkedNode {

    private LinkedNode parent;

    private String parentName;

    private Map<String, Object> data;

    public LinkedNode(LinkedNode parent, String parentName, Map<String, Object> data) {
        this.parent = parent;
        this.parentName = parentName;
        this.data = data;
    }
}

public class JSONFlatProcessor {

    private LinkedList<LinkedNode> nodes;

    private LinkedList<String> column;

    private List<Object[]> data;

    public void find(LinkedNode parent, String parentName, Map<String, Object> data) {
        LinkedNode node = new LinkedNode(parent, parentName, data);
        if (!hasObjectOrArray(data)) {
            nodes.add(node);
        } else {
            for (Map.Entry entry : data.entrySet()) {
                if (entry.getValue() instanceof Map) {
                    find(node, String.valueOf(entry.getKey()), (Map<String, Object>) entry.getValue());
                } else if (isObjectArray(entry.getValue())) {
                    find(node, String.valueOf(entry.getKey()), (List<Map<String, Object>>) entry.getValue());
                }
            }
        }
    }

    public void find(LinkedNode parent, String parentName, List<Map<String, Object>> data) {
        for (Map<String, Object> item : data) {
            find(parent, parentName, item);
        }
    }

    protected Boolean hasObjectOrArray(Map<String, Object> item) {
        Object field;
        for (Map.Entry entry : item.entrySet()) {
            field = entry.getValue();
            if (field instanceof Map || isObjectArray(field)) {
                return Boolean.TRUE;
            }
        }

        return Boolean.FALSE;
    }

    protected Boolean isObjectArray(Object object) {
        return object instanceof List
                && !CollectionUtils.isEmpty((List) object)
                && ((List) object).get(0) instanceof Map;
    }

    public JSONFlatProcessor process(List<Map<String, Object>> data) {
        nodes = new LinkedList<>();
        find(null, null, data);
        return this;
    }

    public JSONFlatProcessor process(Map<String, Object> data) {
        nodes = new LinkedList<>();
        find(null, null, data);
        return this;
    }

    public LinkedList<LinkedNode> getNodes() {
        return nodes;
    }

    public List<String> getColumn() {

        if (CollectionUtils.isEmpty(nodes)) {
            return Collections.emptyList();
        }

        column = new LinkedList<>();
        collectColumn(nodes.getFirst());

        return column;

    }

    protected void collectColumn(LinkedNode node) {
        List<String> innerColumn = new ArrayList<>(node.getData().size());
        String columnBuilder;
        for (Map.Entry entry : node.getData().entrySet()) {
            if (!(entry.getValue() instanceof Map || isObjectArray(entry.getValue()))) {
                columnBuilder = null == node.getParentName()? String.valueOf(entry.getKey()) : String.format("%s.%s", node.getParentName(), entry.getKey());
                innerColumn.add(columnBuilder);
            }
        }
        column.addAll(0, innerColumn);

        if (null != node.getParent()) {
            collectColumn(node.getParent());
        }
    }

    public List<Object[]> getData() {

        if (CollectionUtils.isEmpty(nodes)) {
            return Collections.emptyList();
        }

        data = new ArrayList<>(nodes.size());

        LinkedList<Object> container;

        for (LinkedNode node : nodes) {
            container = new LinkedList<>();
            collectData(node, container);
            data.add(container.toArray());
        }

        return data;

    }

    protected void collectData(LinkedNode node, LinkedList<Object> container) {
        List<Object> innerData = new ArrayList<>(node.getData().size());
        for (Map.Entry entry : node.getData().entrySet()) {
            if (!(entry.getValue() instanceof Map || isObjectArray(entry.getValue()))) {
                innerData.add(entry.getValue());
            }
        }
        container.addAll(0, innerData);

        if (null != node.getParent()) {
            collectData(node.getParent(), container);
        }
    }

    protected static class CollectionUtils {
        public static boolean isEmpty(Collection<?> collection) {
            return (collection == null || collection.isEmpty());
        }
    }

}

public class MainTests {

    public static void main(String[] args) throws Exception {
        String jsonStr = "{\"code\":200,\"requestId\":\"1680177848458\",\"data\":[{\"school\":\"xxx市第一实验小学\",\"no\":\"1001\",\"class\":[{\"name\":\"一(1)班\",\"teacher\":\"吴老师\",\"student\":[{\"name\":\"张同学\",\"age\":6},{\"name\":\"王同学\",\"age\":7}]}]},{\"school\":\"xxx市第二实验小学\",\"no\":\"1002\",\"class\":[{\"name\":\"一(2)班\",\"teacher\":\"陈老师\",\"student\":[{\"name\":\"欧阳同学\",\"age\":6}]}]}]}";
        ObjectMapper jsonMapper = new ObjectMapper();
//        List<Map<String, Object>> map = jsonMapper.readValue(jsonStr, List.class);
        Map<String, Object> map = jsonMapper.readValue(jsonStr, Map.class);


        JSONFlatProcessor processor = new JSONFlatProcessor().process(map);
        System.out.println("数据条数: " + processor.getNodes().size());
        System.out.println("字段名: " + processor.getColumn());
        System.out.println("首行数据: " + new ObjectMapper().writeValueAsString(processor.getData().get(0)));
    }

}

数据条数: 3
字段名: [code, requestId, data.school, data.no, class.name, class.teacher, student.name, student.age]
首行数据: [200,"1680177848458","xxx市第一实验小学","1001","一(1)班","吴老师","张同学",6]