Mybatis自定义TypeHandler实现数据库Json数组转List＜T＞对象

Posted 2022-11-01 赵侠客

实现功能

在开发过程中经常会遇到将整个JSON数据当作一个字段存到数据库中的情况，但是我们在对应实体表中又不想用一个String去接收，如下图，数据库t_user表中有一个address字段，存的是一个JSON数组，TUserEntity实体中使用List<Address> 对象去接收，这时就需要自定义TypeHanlder帮我们定义入库和出库时的JSON序列化和反序列化。

@Data
@TableName("t_user")
public class TUserEntity  implements Serializable 
    private static final long serialVersionUID = 1L;
    private Long id;
    @TableField(typeHandler = AddressListTypeHandler.class)
    private List<Address> address;

    ```
@Data
public class Address implements Serializable 
    private static final long serialVersionUID = 1L;
    private Long id;
    private String name;

```

定义抽象List处理TypeHandler，List中可能还存入其它类型数据

import com.fasterxml.jackson.core.type.TypeReference;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;


public abstract class ListTypeHandler<T> extends BaseTypeHandler<List<T>> 
    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, List<T> parameter, JdbcType jdbcType) throws SQLException 
        ps.setString(i, JsonUtils.toJson(parameter));
    

    @Override
    public List<T> getNullableResult(ResultSet rs, String columnName) throws SQLException 
        return rs.wasNull() ? null : JsonUtils.readList(rs.getString(columnName), specificType());
    

    @Override
    public List<T> getNullableResult(ResultSet rs, int columnIndex) throws SQLException 
        return rs.wasNull() ? null : JsonUtils.readList(rs.getString(columnIndex), specificType());
    

    @Override
    public List<T> getNullableResult(CallableStatement cs, int columnIndex) throws SQLException 
        return cs.wasNull() ? null : JsonUtils.readList(cs.getString(columnIndex), specificType());
    

    protected abstract TypeReference<List<T>> specificType();

定义AddressListTypeHandler类 ,如果有其它类继承ListTypeHandler就可以了

@MappedTypes(List.class)
public class AddressListTypeHandler extends  ListTypeHandler<Address> 
    @Override
    protected TypeReference<List<Address>> specificType() 
        return new TypeReference<List<Address>>() 
        ;
    

jaskson中JsonUtils.readList()方法，也可使用fastjson JSON.parseObject(content, this.specificType())

public static <T> List<T> readList(String json, TypeReference<List<T>> tTypeReference) 
    if (json == null || "".equals(json)) 
        return null;
    
    try 
        return mapper.readValue(json,tTypeReference);
     catch (IOException e) 
        throw new RuntimeException(e);
    

测试结果查询