Lombok 是一个非常受欢迎和有用的图书馆。尽管如此，请注意Lombok @EqualsAndHashCode对实体的影响可能会带来严重问题。
实体应实施equals()和hashCode()。主要问题是Hibernate要求实体在其所有状态转换（瞬态，附加，分离 和删除）中等于自身。使用Lombok @EqualsAndHashCode不会尊重此要求。
避免下面这些方法：
1. 避免使用的Lombok默认行为@EqualsAndHashCode：
@Entity
@EqualsAndHashCode
public class LombokDefaultProduct implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private String code;
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2. 避免使用只有主键的Lombok@EqualsAndHashCode
@Entity
@EqualsAndHashCode(exclude = {"name", "code"})
public class LombokIdProduct implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private String code;
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3. 避免使用默认equals()和hashCode()，下面实体没有编写自己的这两个方法，使用的是默认，不推荐这样做：
@Entity
public class DefaultProduct implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private String code;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
}
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4. 避免使用只依赖主键的equals()和hashCode()：@Entity
public class IdProduct implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private String code;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
@Override
public int hashCode() {
int hash = 3;
hash = 89 * hash + Objects.hashCode(this.id);
return hash;
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final IdProduct other = (IdProduct) obj;
if (!Objects.equals(this.id, other.id)) {
return false;
}
return true;
}
}
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推荐这些方法：1. 依靠@NaturalId
@Entity
public class NaturalIdProduct implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
@NaturalId
@Column(nullable = false, updatable = false, unique = true, length = 50)
private String code;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (!(o instanceof NaturalIdProduct)) {
return false;
}
NaturalIdProduct naturalIdProduct = (NaturalIdProduct) o;
return Objects.equals(getCode(), naturalIdProduct.getCode());
}
@Override
public int hashCode() {
return Objects.hash(getCode());
}
}
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2. 依靠主键：@Entity
public class GoodProduct implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private String code;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (!(obj instanceof GoodProduct)) {
return false;
}
return id != null && id.equals(((GoodProduct) obj).id);
}
@Override
public int hashCode() {
return 2018;
}
}
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良好的equals()和hashCode()：
源代码可以在这里找到