The configuration field of BaseTypeHandler is always null

[L-YDXL]

I customize a class JsonTypeHandler, which inherits BaseTypeHandler. In this class I want to use the inside attribute configuration, but this property is null.

MyBatis version

3.4.5

Database vendor and version

Test case or example project

public class JsonTypeHandler<E> extends BaseTypeHandler<E> {

    private Class<E> type;

    private static final String OBJECT_MAPPER_KEY = ObjectMapper.class.getName();


    public JsonTypeHandler(Class<E> type) {
        if (type == null) {
            throw new IllegalArgumentException("Type argument cannot be null");
        }
        this.type = type;
    }

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, E parameter, JdbcType jdbcType) throws SQLException {
        try {
            ObjectMapper objectMapper = (ObjectMapper) configuration.getVariables().get(OBJECT_MAPPER_KEY);
            ps.setString(i, objectMapper.writeValueAsString(parameter));
        } catch (JsonProcessingException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public E getNullableResult(ResultSet rs, String columnName) throws SQLException {
        String s = rs.getString(columnName);
        return s == null ? null : getE(s);
    }

    @Override
    public E getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        String s = rs.getString(columnIndex);
        return s == null ? null : getE(s);
    }

    private E getE(String s) {
        ObjectMapper objectMapper = (ObjectMapper) configuration.getVariables().get(OBJECT_MAPPER_KEY);
        try {
            return objectMapper.readValue(s, type);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public E getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        String s = cs.getString(columnIndex);
        return s == null ? null : getE(s);
    }
}

Expected result

BaseTypeHandler#configuration is not null

Actual result

BaseTypeHandler#configuration is null

[kazuki43zoo]

@liangzhongqiu , thanks for your reporting.

In the current version(3.4.6), the mybatis does not call the BaseTypeHandler#setConfiguration in the framework processing.
If you use the Configuration instance on your type handler, you should be called the BaseTypeHandler#setConfiguration manually as follows:

Configuration configuration = new Configuration();
JsonTypeHandler typeHandler = new JsonTypeHandler();
typeHandler.setConfiguration(configuration);
configuration.getTypeHandlerRegistry().register(typeHandler);

[kazuki43zoo]

@harawata

I will suggest that call the BaseTypeHandler#setConfiguration in TypeHandlerRegistry#register when typehandler extends the BaseTypeHandler class.

WDYT?

[harawata]

Hi guys,

After looking into the history, I suspect that the field BaseTypeHandler.configuration was added by mistake [1].

The expected solution, in this case, would be to register an instance of the type handler after setting necessary properties (instead of registering the Class).
It would look something like this:

JsonTypeHandler handler = new JsonTypeHandler(type, objectMapper);
configuration.getTypeHandlerRegistry().register(..., handler, ...);

[1] The field is not used at all and removing it does not break any test.
Judging from the old issue comments, the field was used in an early implementation, but not in the final implementation.

[kazuki43zoo]

was added by mistake [1].

I propose to add @Deprecated in 3.5.0 and removing at future (e.g. 4.0.0).

[harawata]

If it's Jackson's ObjectMapper, there seems to be a better way.