Springboot與Jpa整合問題

主要包括兩個問題：

1、查詢結果轉換json時出現異常：

Could not write JSON: No serializer found for class
 org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to 
create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS); 
nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for 
class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to 
create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) 
(through reference chain: 
xxxx->xxxx->java.util.Collections$UnmodifiableRandomAccessList[0]->xxxxx[\"xxxxx\"]->xxxxx_$$_jvst928_69[\"handler\"])"

其實解決這種問題有幾種方案，目前說兩種：

    a.在實體類上加上註解，但是會導致新的問題，那就是關聯的對象加上FetchType.LAZY不起作用了。當然這個註解不用加在每個實體上，寫一個接口去實現就行。

@JsonIgnoreProperties({ "handler","hibernateLazyInitializer","fieldHandler"})

  b.第二種方案，則是通過Hibernate4Module

 添加依賴jar

<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-hibernate4</artifactId>
    <version>2.9.8</version>
</dependency>

編寫類

public class HibernateAwareObjectMapper extends ObjectMapper {

    public HibernateAwareObjectMapper(){
        Hibernate4Module hibernate4Module = new Hibernate4Module();
        hibernate4Module.configure(Hibernate4Module.Feature.USE_TRANSIENT_ANNOTATION, false);
        registerModule(hibernate4Module);
    }

    public void setPrettyPrint(boolean prettyPrint) {
        configure(SerializationFeature.INDENT_OUTPUT, prettyPrint);
    }
}

添加到MessageConverter中

@Bean
public MappingJackson2HttpMessageConverter messageConverter(){
    HibernateAwareObjectMapper hibernateAwareObjectMapper = new HibernateAwareObjectMapper();
    MappingJackson2HttpMessageConverter HttpMessageConverter = new MappingJackson2HttpMessageConverter(hibernateAwareObjectMapper);
    return HttpMessageConverter;
}

但是延遲加載的數據如何查詢出來，這就是第二個需要解決的問題了。

2、處理指定延遲對象加載方案：

@Override
public T getOne(Serializable id, String[] props) {
    T t = repository.findOne(id);
    getRelationObj(t, props);
    return t;
}

private void getRelationObj(T initializeObject, String[] props) {
    if(props!=null){
        for(String prop : props){
            getRelationObj(initializeObject, prop);
        }
    }
}

private void getRelationObj(T initializeObject, String prop) {
    try {
        if(StringUtils.isNotEmpty(prop)){
            Object obj = PropertyUtils.getProperty(initializeObject, prop);
            Hibernate.initialize(obj);
        }
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
    }
}