Hbernate Annotation多对多映射
Annotation用起来真是太方便了，多对多映射很需要很少的几个注解就可以搞定.
需要的jar包是ejb3-persistence.jar（见附件）
实例:用户表：userCREATE TABLE user( id BIGINT NOT NULL, optimistic INT, userName VARCHAR(32), password VARCHAR(128), PRIMARY KEY (id));角色表CREATE TABLE role( id BIGINT NOT NULL, optimistic INT, name VARCHAR(50), active SMALLINT NOT NULL, PRIMARY KEY (id));角色用户关系表CREATE TABLE roles2users( users_fk BIGINT, roles_fk BIGINT)关系表不要映射成实体，也就是说我们的java代码只有2个类，user类和role类。[b]java代码[/b]user对象和role对象都继承自同一个父类，父类封装了id和hibernate版本控制的字段还有equals和hashcode方法：@MappedSuperclasspublic class AutoIDEntity implements java.io.Serializable{ private static final long serialVersionUID = 1L; private Long id; private Integer optimistic; @Id @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="SEQ_STORE") public Long getId() { return this.id; } @Version public Integer getOptimistic() { return this.optimistic; }protected void setId(Long id) {this.id = id;}protected void setOptimistic(Integer optimistic) {this.optimistic = optimistic;}@Overridepublic boolean equals(final Object other) {if (!(other instanceof AutoIDEntity))return false;AutoIDEntity castOther = (AutoIDEntity) other;return new EqualsBuilder().append(id, castOther.getId()).isEquals();}@Overridepublic int hashCode() {return new HashCodeBuilder().append(id).toHashCode();}}[b]User类[/b][size=small][/size]@Entity@org.hibernate.annotations.Cache(usage = org.hibernate.annotations.CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)@SequenceGenerator(name="SEQ_STORE",sequenceName="user_id_sequence")public class User extends AutoIDEntity { /** * 登录名 */ private String userName; /** * 密码 */ private String password; /** * 角色集合 */ private Set<Role> roles = new HashSet<Role>(); @ManyToMany(fetch = FetchType.EAGER) @JoinTable(name = "ROLES2USERS", joinColumns = { @JoinColumn(name = "USERS_FK", nullable = false, insertable = true, updatable = true, columnDefinition = "BIGINT") }, inverseJoinColumns = { @JoinColumn(name = "ROLES_FK", nullable = false, insertable = true, updatable = true, columnDefinition = "BIGINT") } ) public Set<Role> getRoles() { return this.roles; }//省略getter和setter方法}[b]角色实体[/b][size=medium][/size]@Entity@org.hibernate.annotations.Cache(usage = org.hibernate.annotations.CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)@SequenceGenerator(name="SEQ_STORE",sequenceName="role_id_sequence")public class Role extends AutoIDEntity { /** * 角色名 */ private String name; /** * 用户集合 */ private Set<User> users = new HashSet<User>(); /** * 该角色的状态，1为有效，0为无效 */ private boolean active = true; @ManyToMany(fetch = FetchType.LAZY,mappedBy="roles")public Set<User> getUsers() {return users; } //省略其它的getter和setter方法 }