我如何使用休眠方式持久化json對象？

Question

這是我的情況：我有一個帶有屬性的類，該屬性可以是json類型或其他數據結構。

public class MiClase {
private int a;
private Object b;
//Get and Set method

}

我想使用休眠方式持久化此類，但是我也想使用以下代碼：

ObjectMapper m=new ObjectMapper();
m.readValue(json, new TypeReference<MiClase>() {
            });

上面的代碼工作正常，但是當我嘗試將實體保存到數據庫中時，出現以下錯誤：映射具有錯誤的列數：MiClase.b類型：o​​bject然后嘗試更改然后嘗試將de object type更改為byte [ ]，但在使用readValue方法時不能反序列化byte []的實例。 在這種情況下，您推薦我什么策略？ 我正在使用postgresql

Answer 1

我對問題的評估感到失望，我認為它具有所有邏輯，盡管我的英語不是很好，但是該解決方案對我有幫助，允許我將任何數據持久化到數據庫中：解決方案是創建自定義類型：

public  class JacksonUserType implements UserType {

    private static final int[] SQL_TYPES = { Types.LONGVARCHAR };

    @Override
    public boolean equals(Object x, Object y) throws HibernateException {
        if (x == y) {
            return true;
        } else if (x == null || y == null) {
            return false;
        } else {
            return x.equals(y);
        }
    }

    @Override
    public int hashCode(Object x) throws HibernateException {
        return null == x ? 0 : x.hashCode();
    }

    @Override
    public boolean isMutable() {
        return true;
    }

    @Override
    public void nullSafeSet(PreparedStatement st, Object value, int index, SessionImplementor session) throws HibernateException, SQLException {
        if (value == null) {
            st.setString(index, null);
        } else {
            st.setString(index, convertObjectToJson(value));
        }
    }

    @Override
    public Object nullSafeGet(ResultSet rs, String[] names, SessionImplementor session, Object owner) throws HibernateException, SQLException {
        String content = rs.getString(names[0]);
        if(content!=null){
            return convertJsonToObject(content);
        }
        return null;
    }

    Object convertJsonToObject(String content){
        try {
            ObjectMapper mapper = new ObjectMapper();
            JavaType type = createJavaType(mapper);
            return mapper.readValue(content, type);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    String convertObjectToJson(Object object){
        try {
            ObjectMapper mapper = new ObjectMapper();
            mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
            return mapper.writeValueAsString(object);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public Object deepCopy(Object value) throws HibernateException {
        String json = convertObjectToJson(value);
        return convertJsonToObject(json);
    }

    /**
     * Optionnal
     */
    @Override
    public Object replace(Object original, Object target, Object owner)
            throws HibernateException {
        return deepCopy(original);
    }

    /**
     * (optional operation)
     *
     * @param value
     *
     * @throws HibernateException
     */
    @Override
    public Serializable disassemble(Object value) throws HibernateException {
        return (Serializable) deepCopy(value);
    }

    /**
     * (optional operation)
     *
     * @param cached
     * @param owner
     *
     * @return the instance cached
     *
     * @throws HibernateException
     */
    @Override
    public Object assemble(Serializable cached, Object owner)
            throws HibernateException {
        return deepCopy(cached);
    }

    /**
     * By default we are expecting to use a simple object / not a collection (Set, List)
     *
     * @param mapper : instance jackson object mapper
     *
     * @return A jackson JavaType to specify wich object represent the json string representation
     *
     */
    public JavaType createJavaType (ObjectMapper mapper){
        return SimpleType.construct(returnedClass());
    }


    @Override
    public int[] sqlTypes() {
        return SQL_TYPES;
    }

    @Override
    public Class returnedClass() {
        return Object.class;
    }
}

您還可以將抽象類的變體與抽象方法一起使用：returnClass（）而不使用通用Object類型