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
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);
}
}
