Java 使用Jackson序列化集合时出现LazyInitializationException异常

我正在使用AngularJs和Rest服务（RestEasy）构建一个应用程序，其中我需要显示产品列表。当用户单击其中一个产品时加载列表后，将加载此产品的详细信息和图像

当我显示所有产品的列表时，我不想加载与产品（即图像）关联的集合，但仅当我需要其中一个产品的详细信息时，出于性能原因，所以我使用延迟加载

Hibernate做得很好，我可以看到，最初我只加载了一些atributes，但没有加载集合，但是在rest服务中，当Jackson试图访问集合对其进行序列化时，我遇到了一个著名的异常：

Caused by: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.domainmodel.Product.Images

当然，此时不再打开会话，数据库事务已提交。我不想让会议一直开着。因此，在网上搜索时，我发现我们可以告诉Jackson不要使用注释@JsonIgnore序列化属性。 此注释必须放在实体（POJO）的属性或getter中，因此基本上，如果我告诉Jackson在序列化为JSON时不要序列化此集合，它将暂时解决问题，但一旦我需要加载产品时，因为用户单击了该集合，它不会序列化集合，因此我稍后会遇到此问题。所以我不认为这是我的解决方案。关于如何解决这种情况有什么想法和建议吗？？我在这里发布了实体和rest服务的代码。提前谢谢你

@Entity
@Table(name = "PRODUCTS")
public class Product implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "ID")
private Long id;

@Column(name = "PATH_TO_IMAGE", nullable = false, insertable = true, updatable = true)
private String pathToImage;

@Column(name="DESCRIPTION",nullable=true, insertable = true, updatable = true)
private String description;

@ManyToOne(optional = false)
@JoinColumn(name = "XID_PRODUCT_TYPE", nullable = false, insertable = false, updatable = false)
private ProductType productType;


@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(
        name = "PRODUCT_IMAGE",
        joinColumns = {@JoinColumn(name = "XID_PRODUCT", referencedColumnName = "ID")},
        inverseJoinColumns = {@JoinColumn(name = "XID_IMAGE", referencedColumnName = "ID")})
private List<Image> images;

... getters and setters 
}

---

您可以在JPA会话中运行Jackson，因此延迟加载将起作用。

您可以做几件事

最快的方法-在返回结果之前，循环查看

产品

并调用每个产品上的

setImages（null）

为

产品

注册两个自定义JSON序列化程序，一个会序列化图像，另一个不会，然后根据调用的服务选择序列化程序。问题是，我不确定用RestEasy是否可以做到这一点，但请看一些提示

不要从REST服务返回您的实体bean，而是使用DTO，这样您就可以轻松地控制返回的内容和格式。另一个巨大的优点是，您将REST层与实体bean分离，这使您可以自由地更改实体，而无需担心更改REST用户期望的格式。这将是首选方案

---

你可以考虑两种可能的选择：

为您的服务层使用单独的数据传输对象（DTO），这样您就可以在实体->DTO转换期间管理所需信息的获取。这种方法的缺点是，您需要编写和维护这些转换器。另一方面，您可以完全灵活地将任何实体组合到服务响应中。首选选项

创建单独的轻量级实体（例如“ProductInfo”），用于“产品”调用。将多个实体映射到一个DB表应该不会有任何问题

---

杰克逊项目的人员开发了一个很好的模块来解决这个问题

在github上查看它，网址为：

---

看起来您遇到了一个sesion问题：`无法初始化代理-没有会话`您会怎么做？

setImages（null）

版本与选项3一起挽救了我的生命。！

@Path("/products")
public class ProductsService extends CommonService{

private static final Logger log =  Logger.getLogger(ProductsService.class);


@EJB
private ProductsServiceHandler handler;

@GET
@Produces(MediaType.APPLICATION_JSON)
public Response getAllProducts(@Context Request request, @Context HttpHeaders httpHeaders)
{
    try
    {
        List<Product> products=handler.findAllProducts();
        return Response.ok(products).header(ALLOW_ORIGIN_HEADER, "*").build();
    }
    catch(Exception e){return Response.status(Status.INTERNAL_SERVER_ERROR).build();}
}

}

 2015-02-03 00:35:41,085 ERROR [io.undertow.request] (default task-9) UT005023: Exception handling request to /arenaclub/rest/products: org.jboss.resteasy.spi.UnhandledException: Response is committed, can't handle exception
at org.jboss.resteasy.core.SynchronousDispatcher.writeException(SynchronousDispatcher.java:148) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.SynchronousDispatcher.writeResponse(SynchronousDispatcher.java:432) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:376) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:179) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:220) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51) [resteasy-jaxrs-3.0.8.Final.jar:]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) [jboss-servlet-api_3.1_spec-1.0.0.Final.jar:1.0.0.Final]
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:61) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:113) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:56) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:45) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:61) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:58) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:70) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.security.handlers.SecurityInitialHandler.handleRequest(SecurityInitialHandler.java:76) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:240) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:227) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:73) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:146) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:177) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:727) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [rt.jar:1.8.0_25]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [rt.jar:1.8.0_25]
at java.lang.Thread.run(Thread.java:745) [rt.jar:1.8.0_25]
Caused by: com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.fgonzalez.domainmodel.Product.images, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->com.fgonzalez.domainmodel.Product["images"])
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:232) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:197) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:187) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:652) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:152) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:100) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:21) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.std.AsArraySerializerBase.serialize(AsArraySerializerBase.java:183) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:114) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:610) [jackson-databind-2.3.2.jar:2.3.2]
at org.jboss.resteasy.plugins.providers.jackson.ResteasyJackson2Provider.writeTo(ResteasyJackson2Provider.java:186) [resteasy-jackson2-provider-3.0.8.Final.jar:]
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.writeTo(AbstractWriterInterceptorContext.java:129) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.interception.ServerWriterInterceptorContext.writeTo(ServerWriterInterceptorContext.java:62) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:118) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.security.doseta.DigitalSigningInterceptor.aroundWriteTo(DigitalSigningInterceptor.java:143) [resteasy-crypto-3.0.8.Final.jar:]
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:122) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.plugins.interceptors.encoding.GZIPEncodingInterceptor.aroundWriteTo(GZIPEncodingInterceptor.java:100) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:122) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.ServerResponseWriter.writeNomapResponse(ServerResponseWriter.java:99) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.SynchronousDispatcher.writeResponse(SynchronousDispatcher.java:427) [resteasy-jaxrs-3.0.8.Final.jar:]
... 32 more