No serializer found for class org.hibernate.proxy.

使用SpringMVC4+Hibernate4+Json時，報錯以下：

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: entity.User_$$_jvst719_0["handler"])
	com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:69)
	com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:32)
	com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:693)
	com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:675)
	com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:157)
	com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:130)
	com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1387)
	com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:889)
	org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:264)
	org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:100)
	org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:202)
	org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor.handleReturnValue(HttpEntityMethodProcessor.java:186)
	org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:80)
	org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:126)
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:806)
	org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:729)
	org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.orm.hibernate4.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:151)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:85)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

致使這一問題的緣由是：json序列化咱們的實體類時，咱們的實體類尚未成功加載。即懶加載（我用的hibernateTemplate.load()）晚於序列化致使(參見http://stackoverflow.com/questions/24994440/no-serializer-found-for-class-org-hibernate-proxy-pojo-javassist-javassist)：

The problem is that entities are loaded lazy and serialization happens before they get loaded fully.

解決辦法是：

1.在實體類前加上：

@Entity
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
public class User {
	private long id; 
	private String name;
	private Double salary;
	...............
}

我理解是讓json忽略掉懶加載的序列化操做，即對於懶加載的，不進行序列化。

2.將獲取對象時的load，改成get(),如將

hibernateTemplate.load(User.class, id);

改成

hibernateTemplate.get(User.class, id);