Java 使用spring反序列化JSON：未解析的前向引用异常

我与Spring一起从事API Rest项目。 我有一个服务“createMaterials”，它将JSON作为参数数据：

装备对象的JSON

{
  "agence": 1, 
  "code": "001",
  "type": "MyType"
}

“装备”与“代理”之间存在多对一的关系。我放置了一个@JsonIdentityInfo标记来使用代理的Id，而不是代理的对象（在看到之后）

但当我在POST/Materials上发送JSON时，我有一个例外：

2017-05-16 18:00:53.021  WARN 8080 --- [nio-8080-exec-8] .w.s.m.s.DefaultHandlerExceptionResolver : Failed to read HTTP message: org.springframework.http.converter.HttpMessageNotReadableException: Could not read document: Unresolved forward references for: 
 at [Source: java.io.PushbackInputStream@767dfd7a; line: 5, column: 1]Object id [1] (for fr.app.domain.Agence) at [Source: java.io.PushbackInputStream@767dfd7a; line: 2, column: 14].; nested exception is com.fasterxml.jackson.databind.deser.UnresolvedForwardReference: Unresolved forward references for: 
 at [Source: java.io.PushbackInputStream@767dfd7a; line: 5, column: 1]Object id [1] (for fr.app.domain.Agence) at [Source: java.io.PushbackInputStream@767dfd7a; line: 2, column: 14].

经过多次研究，我看到了ObjectDresolver在JsonIdentityInfo中的使用。。。 但我认为这不是最好的解决办法。这就是为什么我请求你帮助找出问题的根源。 谢谢

materialcontroller.java

package fr.app.controllers;

import fr.app.domain.Materiel;
import fr.app.services.MaterielService;
import org.springframework.web.bind.annotation.*;

import javax.annotation.Resource;
import java.util.Collection;

@RestController @RequestMapping(value = "/materiels")
public class MaterielController {
    @Resource
    private MaterielService materielService;

    @RequestMapping(method = RequestMethod.POST)
    public Materiel createMateriel(@RequestBody Materiel materiel) {
        return this.materielService.createMateriel(materiel);
    }

    @RequestMapping(method = RequestMethod.GET)
    public Collection<Materiel> getAllMateriels() {
        return this.materielService.getAllMateriels();
    }

    @RequestMapping(value = "/{code}", method = RequestMethod.GET)
    public Materiel getMaterielByCode(@PathVariable(value = "code") String code) {
        //find materiel by code
        return this.materielService.getMaterielByCode(code);

    }

    @RequestMapping(value = "/{id}", method = RequestMethod.DELETE)
    public void deleteMateriel(@PathVariable(value = "id") Long id) {
        this.materielService.deleteMateriel(id);

    }

    @RequestMapping(value = "/{id}", method = RequestMethod.PUT)
    public Materiel updateMateriel(@PathVariable(value = "id") Long id, @RequestBody
            Materiel materiel) {

            materiel.setIdMateriel(id);

        return this.materielService.updateMateriel(materiel);

    }
}

package fr.app.domain;

import com.fasterxml.jackson.annotation.*;

import javax.persistence.*;

@Entity
public class Materiel {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long idMateriel;

    @Column(name = "type_materiel", nullable = false)
    private String type;

    @Column(name = "code_materiel", unique = true, nullable = false)
    private String code;

    @JsonIdentityInfo(
            generator = ObjectIdGenerators.PropertyGenerator.class,
            property = "idAgence")
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "agence")
    private Agence agence;

    public Materiel() {    }

    public Materiel(String type, String code, String dateScan) {
        this.type = type;
        this.code = code;
        this.dateScan = dateScan;
    }

    public Long getIdMateriel() {
        return idMateriel;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public Agence getAgence() {
        return agence;
    }

    public void setAgence(Agence agence) {
        if(this.agence != null)
            this.agence.deleteMateriel(this);
        this.agence = agence;
        this.agence.addMateriel(this);
    }
}

package fr.app.services;

import fr.app.domain.Materiel;
import fr.app.repositories.MaterielRepository;
import org.apache.commons.collections.IteratorUtils;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;
import java.util.Collection;

@Service(value = "materielService")
public class MaterielServiceImpl implements MaterielService {
    @Resource
    private MaterielRepository materielRepository;

    ...

    @Override
    public Materiel createMateriel(Materiel materiel) {
        return this.materielRepository.save(materiel);
    }

   ...
}

package fr.app.domain;

import com.fasterxml.jackson.annotation.*;

import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;

@Entity
public class Agence {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long idAgence;

    @Column(name = "nom",unique = true, nullable = false)
    private String nom;

    @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "agence")
    private Set<Materiel> materiels = new HashSet<Materiel>();

    public Agence() { }

    public Agence(String nom) {
        this.nom = nom;
    }

    public Long getIdAgence() {
        return idAgence;
    }

    public String getNom() {
        return nom;
    }

    public void setNom(String nom) {
        this.nom = nom;
    }

    public Set<Materiel> getMateriels() {
        return materiels;
    }

    public void setMateriels(Set<Materiel> materiels) {
        this.materiels = materiels;
    }

    public void addMateriel(Materiel materiel) {
        this.materiels.add(materiel);
    }

    public void deleteMateriel(Materiel materiel) {
        this.materiels.remove(materiel);
    }

}

materialservice.java

package fr.app.controllers;

import fr.app.domain.Materiel;
import fr.app.services.MaterielService;
import org.springframework.web.bind.annotation.*;

import javax.annotation.Resource;
import java.util.Collection;

@RestController @RequestMapping(value = "/materiels")
public class MaterielController {
    @Resource
    private MaterielService materielService;

    @RequestMapping(method = RequestMethod.POST)
    public Materiel createMateriel(@RequestBody Materiel materiel) {
        return this.materielService.createMateriel(materiel);
    }

    @RequestMapping(method = RequestMethod.GET)
    public Collection<Materiel> getAllMateriels() {
        return this.materielService.getAllMateriels();
    }

    @RequestMapping(value = "/{code}", method = RequestMethod.GET)
    public Materiel getMaterielByCode(@PathVariable(value = "code") String code) {
        //find materiel by code
        return this.materielService.getMaterielByCode(code);

    }

    @RequestMapping(value = "/{id}", method = RequestMethod.DELETE)
    public void deleteMateriel(@PathVariable(value = "id") Long id) {
        this.materielService.deleteMateriel(id);

    }

    @RequestMapping(value = "/{id}", method = RequestMethod.PUT)
    public Materiel updateMateriel(@PathVariable(value = "id") Long id, @RequestBody
            Materiel materiel) {

            materiel.setIdMateriel(id);

        return this.materielService.updateMateriel(materiel);

    }
}

package fr.app.domain;

import com.fasterxml.jackson.annotation.*;

import javax.persistence.*;

@Entity
public class Materiel {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long idMateriel;

    @Column(name = "type_materiel", nullable = false)
    private String type;

    @Column(name = "code_materiel", unique = true, nullable = false)
    private String code;

    @JsonIdentityInfo(
            generator = ObjectIdGenerators.PropertyGenerator.class,
            property = "idAgence")
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "agence")
    private Agence agence;

    public Materiel() {    }

    public Materiel(String type, String code, String dateScan) {
        this.type = type;
        this.code = code;
        this.dateScan = dateScan;
    }

    public Long getIdMateriel() {
        return idMateriel;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public Agence getAgence() {
        return agence;
    }

    public void setAgence(Agence agence) {
        if(this.agence != null)
            this.agence.deleteMateriel(this);
        this.agence = agence;
        this.agence.addMateriel(this);
    }
}

package fr.app.services;

import fr.app.domain.Materiel;
import fr.app.repositories.MaterielRepository;
import org.apache.commons.collections.IteratorUtils;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;
import java.util.Collection;

@Service(value = "materielService")
public class MaterielServiceImpl implements MaterielService {
    @Resource
    private MaterielRepository materielRepository;

    ...

    @Override
    public Materiel createMateriel(Materiel materiel) {
        return this.materielRepository.save(materiel);
    }

   ...
}

package fr.app.domain;

import com.fasterxml.jackson.annotation.*;

import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;

@Entity
public class Agence {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long idAgence;

    @Column(name = "nom",unique = true, nullable = false)
    private String nom;

    @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "agence")
    private Set<Materiel> materiels = new HashSet<Materiel>();

    public Agence() { }

    public Agence(String nom) {
        this.nom = nom;
    }

    public Long getIdAgence() {
        return idAgence;
    }

    public String getNom() {
        return nom;
    }

    public void setNom(String nom) {
        this.nom = nom;
    }

    public Set<Materiel> getMateriels() {
        return materiels;
    }

    public void setMateriels(Set<Materiel> materiels) {
        this.materiels = materiels;
    }

    public void addMateriel(Materiel materiel) {
        this.materiels.add(materiel);
    }

    public void deleteMateriel(Materiel materiel) {
        this.materiels.remove(materiel);
    }

}

agent.java

package fr.app.controllers;

import fr.app.domain.Materiel;
import fr.app.services.MaterielService;
import org.springframework.web.bind.annotation.*;

import javax.annotation.Resource;
import java.util.Collection;

@RestController @RequestMapping(value = "/materiels")
public class MaterielController {
    @Resource
    private MaterielService materielService;

    @RequestMapping(method = RequestMethod.POST)
    public Materiel createMateriel(@RequestBody Materiel materiel) {
        return this.materielService.createMateriel(materiel);
    }

    @RequestMapping(method = RequestMethod.GET)
    public Collection<Materiel> getAllMateriels() {
        return this.materielService.getAllMateriels();
    }

    @RequestMapping(value = "/{code}", method = RequestMethod.GET)
    public Materiel getMaterielByCode(@PathVariable(value = "code") String code) {
        //find materiel by code
        return this.materielService.getMaterielByCode(code);

    }

    @RequestMapping(value = "/{id}", method = RequestMethod.DELETE)
    public void deleteMateriel(@PathVariable(value = "id") Long id) {
        this.materielService.deleteMateriel(id);

    }

    @RequestMapping(value = "/{id}", method = RequestMethod.PUT)
    public Materiel updateMateriel(@PathVariable(value = "id") Long id, @RequestBody
            Materiel materiel) {

            materiel.setIdMateriel(id);

        return this.materielService.updateMateriel(materiel);

    }
}

package fr.app.domain;

import com.fasterxml.jackson.annotation.*;

import javax.persistence.*;

@Entity
public class Materiel {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long idMateriel;

    @Column(name = "type_materiel", nullable = false)
    private String type;

    @Column(name = "code_materiel", unique = true, nullable = false)
    private String code;

    @JsonIdentityInfo(
            generator = ObjectIdGenerators.PropertyGenerator.class,
            property = "idAgence")
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "agence")
    private Agence agence;

    public Materiel() {    }

    public Materiel(String type, String code, String dateScan) {
        this.type = type;
        this.code = code;
        this.dateScan = dateScan;
    }

    public Long getIdMateriel() {
        return idMateriel;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public Agence getAgence() {
        return agence;
    }

    public void setAgence(Agence agence) {
        if(this.agence != null)
            this.agence.deleteMateriel(this);
        this.agence = agence;
        this.agence.addMateriel(this);
    }
}

package fr.app.services;

import fr.app.domain.Materiel;
import fr.app.repositories.MaterielRepository;
import org.apache.commons.collections.IteratorUtils;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;
import java.util.Collection;

@Service(value = "materielService")
public class MaterielServiceImpl implements MaterielService {
    @Resource
    private MaterielRepository materielRepository;

    ...

    @Override
    public Materiel createMateriel(Materiel materiel) {
        return this.materielRepository.save(materiel);
    }

   ...
}

package fr.app.domain;

import com.fasterxml.jackson.annotation.*;

import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;

@Entity
public class Agence {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long idAgence;

    @Column(name = "nom",unique = true, nullable = false)
    private String nom;

    @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "agence")
    private Set<Materiel> materiels = new HashSet<Materiel>();

    public Agence() { }

    public Agence(String nom) {
        this.nom = nom;
    }

    public Long getIdAgence() {
        return idAgence;
    }

    public String getNom() {
        return nom;
    }

    public void setNom(String nom) {
        this.nom = nom;
    }

    public Set<Materiel> getMateriels() {
        return materiels;
    }

    public void setMateriels(Set<Materiel> materiels) {
        this.materiels = materiels;
    }

    public void addMateriel(Materiel materiel) {
        this.materiels.add(materiel);
    }

    public void deleteMateriel(Materiel materiel) {
        this.materiels.remove(materiel);
    }

}

包fr.app.domain；
导入com.fasterxml.jackson.annotation.*；
导入javax.persistence.*；
导入java.util.HashSet；
导入java.util.Set；
@实体
公共类代理{
@身份证
@GeneratedValue（策略=GenerationType.AUTO）
私人长期代理；
@列（name=“nom”，unique=true，nullable=false）
私有字符串名称；
@OneToMany（fetch=FetchType.LAZY，cascade=CascadeType.ALL，mappedBy=“agence”）
私有集合materials=newhashset（）；
公共机构（）{}
公共代理（字符串名称）{
this.nom=nom；
}
公共长期代理（）{
返回代理；
}
公共字符串getNom（）{
返回名称；
}
公共无效集合名（字符串名）{
this.nom=nom；
}
公共集getMaterials（）{
退货材料；
}
公共空间集合材料（集合材料）{
this.materials=materials；
}
公共装备（装备）{
本.物料.添加（物料）；
}
公共物资（装备）{
此。物料。移除（物料）；
}
}

pom.xml

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.6</version>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>commons-collections</groupId>
        <artifactId>commons-collections</artifactId>
        <version>3.0</version>
    </dependency>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>5.2.9.Final</version>
    </dependency>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-entitymanager</artifactId>
        <version>5.2.9.Final</version>
    </dependency>
    <dependency>
        <groupId>io.springfox</groupId>
        <artifactId>springfox-swagger2</artifactId>
        <version>2.6.1</version>
    </dependency>
    <dependency>
        <groupId>io.springfox</groupId>
        <artifactId>springfox-swagger-ui</artifactId>
        <version>2.2.2</version>
        <scope>compile</scope>
    </dependency>

    <!-- Needed for JSON View -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.8.6</version>
    </dependency>
</dependencies>

org.springframework.boot
spring引导启动器数据jpa
mysql
mysql连接器java
5.1.6
org.springframework.boot
弹簧起动试验
测试
org.springframework.boot
SpringBootStarterWeb
公地收藏
公地收藏
3
org.hibernate
冬眠核心
5.2.9.最终版本
org.hibernate
休眠实体管理器
5.2.9.最终版本
伊奥·斯普林福克斯
springfox-Swagger 2
2.6.1
伊奥·斯普林福克斯
springfox招摇过市用户界面
2.2.2
编译
com.fasterxml.jackson.core
杰克逊数据绑定
2.8.6

您有两个域：装备和代理。当Jackson试图反序列化装备时，它调用方法

getAgence

。此方法返回一个代理对象，Jackson也将对该对象进行反序列化。当Jackson调用（Agence的）getMeteries方法时，它返回一组也将反序列化的装备。问题是Jackson将再次尝试反序列化集合中的每种装备。同样的so问题。

对于最后一个异常（utf-8），您可以更改控制器的签名，如下所示：

@RequestMapping(method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_VALUE, consumes = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Bean> create(HttpServletRequest  request) throws IOException {
    // getting the posted value
    String body = CharStreams.toString(request.getReader());
    Bean bean = new ObjectMapper().readValue(body, service.getBeanClass());
    bean.setId(null);
    Bean saved = service.save(bean);

    URI location = ServletUriComponentsBuilder.fromCurrentRequest().path("/{id}").buildAndExpand(saved.getId()).toUri();
    return ResponseEntity.created(location).body(saved);
}

@RequestMapping（method=RequestMethod.POST，products=MediaType.APPLICATION\u JSON\u VALUE，consumes=MediaType.APPLICATION\u JSON\u VALUE）
公共响应属性创建（HttpServletRequest请求）引发IOException{
//获取过账价值
String body=CharStreams.toString（request.getReader（））；
Bean=newObjectMapper（）.readValue（body，service.getBeanClass（））；
setId（null）；
保存的Bean=service.save（Bean）；
URI location=ServletUriComponentsBuilder.fromCurrentRequest（）.path（“/{id}”）.buildAndExpand（saved.getId（））.toUri（）；
返回ResponseEntity.created（location）.body（saved）；
}

使用此解决方案，您可以完全控制映射

---

享受

好的，我发现了问题

最后，我需要添加解析器。因此，我找到了implement

ObjectdResolver

的一个示例：

import com.fasterxml.jackson.annotation.ObjectIdGenerator;
import com.fasterxml.jackson.annotation.ObjectIdResolver;

import javax.persistence.EntityManager;

/**
 * @author fta on 20.12.15.
 */

public class EntityIdResolver
        implements ObjectIdResolver {

    private EntityManager entityManager;

    public EntityIdResolver(
            final EntityManager entityManager) {

        this.entityManager = entityManager;

    }

    @Override
    public void bindItem(
            final ObjectIdGenerator.IdKey id,
            final Object pojo) {

    }

    @Override
    public Object resolveId(final ObjectIdGenerator.IdKey id) {

        return this.entityManager.find(id.scope, id.key);
    }

    @Override
    public ObjectIdResolver newForDeserialization(final Object context) {

        return this;
    }

    @Override
    public boolean canUseFor(final ObjectIdResolver resolverType) {

        return false;
    }

}

接下来我添加

@JsonIdentityInfo

：

@Entity
@JsonIdentityInfo(
        generator = ObjectIdGenerators.PropertyGenerator.class,
        property = "idAgence",
        resolver = EntityIdResolver.class,
        scope=Agence.class)
public class Agence {
    // ... 
}

---

由于一对多关系，您似乎有一个循环对象图。对于那些您可以使用

它可以处理循环对象图的序列化和反序列化（自Jackson 2.5.1以来）

---

Matiriel

引用了

Agency

，

Agency

引用了

Matiriel

，导致循环引用。您需要向其中一个添加

@JsonIgnore

。