接口作用
MongoDB中，列的类型不同（Array类型，Object类型），在转换成为二维表的时候，就会有不同的处理方式。
从MongoDB数据集插件8.4+版本，提供接口可自行开发插件，处理更为复杂的类型的列。
接口内容
public interface ColumnResolver extends Mutable {
String MARK_STRING = "ColumnResolver";
int CURRENT_LEVEL = 1;
boolean checkIfConditionMeet(ColumnResolver resolver);
/**
* 是否需要处理该类型的元素
*
* @param cell doc查询出来的对象
* @return 需要做扩展处理则返回true，否则返回false
*/
boolean accept(Object cell);
/**
* 增加新的列
*
* @param key 列名
* @param cell 内容
*/
List<FieldObject> expandColumn(String key, Object cell);
/**
* 扩展特殊列，增加新的行
*
* @param doc MongoDB的文档查询对象
* @param columnNames 列名集合
* @param columnResolverMap 需要特殊处理的列以及处理器集合
* @param rowDataCollections 扩展出来的行数据集合
* @param rowData 当前行数据
*/
void expandData(Document doc, List<String> columnNames,
Map<FieldObject, ColumnResolver> columnResolverMap,
List<List<Object>> rowDataCollections,
List<Object> rowData);
}
示例实现（数组类型）
我们以数组元素为例子，面对这样的数据结构：
{
"name" : "李四",
"age" : 15,
"language" : [
"英语",
"数学",
"物理"
],
"region" : [
"新疆",
"海南",
"台湾"
],
"country" : "US"
}
当需要把表格转换为二维表的时候，就需要处理language和region这样的数组元素，可以通过实现接口com.fr.plugin.db.mongo.expand.ColumnResolver，来把数组自动扩张开，示例代码如下：
public class ArrayColumnResolver extends AbstractColumnResolver {
@Override
public boolean accept(Object cell) {
return cell instanceof ArrayList
&& !(((ArrayList) cell).get(0) instanceof Document);
}
@Override
public List<FieldObject> expandColumn(String key, Object cell) {
List<FieldObject> data = new ArrayList<FieldObject>();
data.add(FieldObject.create(key));
return data;
}
@Override
public void expandData(Document doc, List<String> columnNames, Map<FieldObject, ColumnResolver> columnResolverMap, List<List<Object>> rowDataCollections, List<Object> rowData) {
Map<Integer, List<Object>> group = new HashMap<Integer, List<Object>>();
List<Object> standard = null;
int maxLength = 0;
for (Map.Entry<FieldObject, ColumnResolver> entry : columnResolverMap.entrySet()) {
if (!checkIfConditionMeet(entry.getValue())) {
continue;
}
FieldObject fieldObject = entry.getKey();
Object data = doc.get(fieldObject.getOriginalName());
if (data instanceof ArrayList) {
List<Object> array = (List<Object>) data;
if (standard == null) {
standard = array;
}
maxLength = Math.max(maxLength, array.size());
group.put(fieldObject.getIndex(), array);
}
}
if (standard != null) {
for (int i = 0; i < maxLength; i++) {
List<Object> row = new ArrayList<Object>(Arrays.asList(new Object[rowData.size()]));
Collections.copy(row, rowData);
for (FieldObject fieldObject : columnResolverMap.keySet()) {
List<Object> array = group.get(fieldObject.getIndex());
row.set(fieldObject.getIndex(), array.size() > i ? array.get(i) : null);
}
rowDataCollections.add(row);
}
}
}
}
示例实现（数组对象类型）
我们以数组元素为例子，面对这样的数据结构：
{
"TEST_ID" : "8376",
"Section_Name" : "大三李",
"ItemList" : [
{
"Item_Name" : "AAA",
"Item_Value" : "123"
},
{
"Item_Name" : "BBB",
"Item_Value" : "456"
},
{
"Item_Name" : "CCC",
"Item_Value" : "789"
}
]
}
希望展现成下面形式的二维表：
同样可以通过实现接口com.fr.plugin.db.mongo.expand.ColumnResolver来实现，示例代码如下：
public class ArrayMapColumnResolver extends AbstractColumnResolver {
@Override
public boolean accept(Object cell) {
return cell instanceof ArrayList && ((ArrayList) cell).get(0) instanceof Document;
}
@Override
public List<FieldObject> expandColumn(String key, Object cell) {
List<FieldObject> expand = new ArrayList<FieldObject>();
if (cell instanceof ArrayList) {
Document document = (Document) ((ArrayList) cell).get(0);
for (String name : document.keySet()) {
expand.add(FieldObject.create(key, name));
}
}
return expand;
}
@Override
public void expandData(Document doc,
List<String> columnNames,
Map<FieldObject, ColumnResolver> columnResolverMap,
List<List<Object>> rowDataCollections,
List<Object> rowData) {
boolean expanded = false;
List<List<Object>> rowList = new ArrayList<List<Object>>();
for (Map.Entry<FieldObject, ColumnResolver> entry : columnResolverMap.entrySet()) {
if (!checkIfConditionMeet(entry.getValue())) {
continue;
}
FieldObject fieldObject = entry.getKey();
List<Document> children = (ArrayList<Document>) doc.get(fieldObject.getOriginalName());
for (int i = 0, size = children.size(); i < size; i ++) {
Document document = children.get(i);
if (!expanded) {
List<Object> row = new ArrayList<Object>(Arrays.asList(new Object[rowData.size()]));
Collections.copy(row, rowData);
row.set(fieldObject.getIndex(), document.get(fieldObject.getCurrentName()));
rowDataCollections.add(row);
rowList.add(row);
} else {
rowList.get(i).set(fieldObject.getIndex(), document.get(fieldObject.getCurrentName()));
}
}
expanded = true;
}
}
}
注册方式
<dependence>
<Item key="com.fr.solution.plugin.db.mongo" type="plugin"/>
</dependence>
<extra-core>
<ColumnResolver class="com.fr.plugin.db.mongo.expand.impl.ArrayColumnResolver"/>
</extra-core>
使用方式
同时安装MongoDB插件和列处理插件，就可以实现自已的要求了。
