【JSON 注解】JSON循环引用1-----Jackson常用注解介绍 eq:@JsonIgnore

循环引用：实体A与实体B有关系，A中有B作为字段，B中有A作为一个字段。查询A对象后，将A对象转化为JSON格式数据时，会因为序列化过程中导致A中有B字段，B字段中又有A，这样就引起了循环引用的问题！！

即如下的解释：

如果A对象持有B的引用，B对象持有A的引用，这样就形成了循环引用，如果直接使用json-lib转换，会报错：

net.sf.json.JSONException: There is a cycle in the hierarchy!

错误由来：

maven搭建的项目使用spring+hibernate+springMVC

两个实体类： Product产品类：Disease疾病类（1：n）关系

Product.java实体类：

  1 package com.agen.entity;
  2 
  3 import java.util.HashSet;
  4 import java.util.Set;
  5 
  6 import javax.persistence.CascadeType;
  7 import javax.persistence.Column;
  8 import javax.persistence.Entity;
  9 import javax.persistence.FetchType;
 10 import javax.persistence.GeneratedValue;
 11 import javax.persistence.Id;
 12 import javax.persistence.OneToMany;
 13 import javax.persistence.Table;
 14 
 15 import org.hibernate.annotations.GenericGenerator;
 16 
 17 import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
 18 
 19 /**
 20  * Product entity. @author MyEclipse Persistence Tools
 21  */
 22 @Entity
 23 @Table(name = "product", catalog = "biologyinfo")
 24 public class Product implements java.io.Serializable {
 25 
 26     // Fields
 27 
 28     /**
 29      * 
 30      */
 31     private static final long serialVersionUID = 1L;
 32     private String productId;
 33     private String productName;
 34     private String productPath;
 35     private Integer productOrder;
 36     private String productCre;
 37     private Set<Disease> diseases = new HashSet<Disease>(0);
 38 
 39     // Constructors
 40 
 41     /** default constructor */
 42     public Product() {
 43     }
 44 
 45     /** full constructor */
 46     public Product(String productName, String productPath,
 47             Integer productOrder, String productCre, Set<Disease> diseases) {
 48         this.productName = productName;
 49         this.productPath = productPath;
 50         this.productOrder = productOrder;
 51         this.productCre = productCre;
 52         this.diseases = diseases;
 53     }
 54 
 55     // Property accessors
 56     @GenericGenerator(name = "generator", strategy = "uuid.hex")
 57     @Id
 58     @GeneratedValue(generator = "generator")
 59     @Column(name = "productId", unique = true, nullable = false, length = 36)
 60     public String getProductId() {
 61         return this.productId;
 62     }
 63 
 64     public void setProductId(String productId) {
 65         this.productId = productId;
 66     }
 67 
 68     @Column(name = "productName", length = 30)
 69     public String getProductName() {
 70         return this.productName;
 71     }
 72 
 73     public void setProductName(String productName) {
 74         this.productName = productName;
 75     }
 76 
 77     @Column(name = "productPath", length = 200)
 78     public String getProductPath() {
 79         return this.productPath;
 80     }
 81 
 82     public void setProductPath(String productPath) {
 83         this.productPath = productPath;
 84     }
 85 
 86     @Column(name = "productOrder")
 87     public Integer getProductOrder() {
 88         return this.productOrder;
 89     }
 90 
 91     public void setProductOrder(Integer productOrder) {
 92         this.productOrder = productOrder;
 93     }
 94 
 95     @Column(name = "productCre", length = 500)
 96     public String getProductCre() {
 97         return this.productCre;
 98     }
 99 
100     public void setProductCre(String productCre) {
101         this.productCre = productCre;
102     }
103 
104     @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "product")
105     public Set<Disease> getDiseases() {
106         return this.diseases;
107     }
108 
109     public void setDiseases(Set<Disease> diseases) {
110         this.diseases = diseases;
111     }
112 
113 }

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