How to create join table with JPA annotations?

You definitely shouldn't create User_Group entity as it's more the underlying database representation than the object oriented one.

You can achieve the join table by defining something like:

@Entity@Table(name="USERS", schema="ADMIN")public class User implements Serializable {//...@ManyToOne@JoinTable(name="USER_GROUP")Group group;

@Entity@Table(name="GROUPS", schema="ADMIN")public class Group implements Serializable {//...@OneToMany(mappedBy="group")Set<User> users;

Edit: If you want to explicitly set the names of the columns you could use @JoinColumn elements as shown below:

@ManyToOne@JoinTable(name="USER_GROUP",    joinColumns = @JoinColumn(name = "userid",                               referencedColumnName = "userid"),     inverseJoinColumns = @JoinColumn(name = "groupid",                               referencedColumnName = "groupid"))Group group;

I would implement it this way:

@Entity@Table(name="GROUPS", schema="ADMIN")public class Group implements Serializable {  @OneToMany  @JoinTable(name = "USER_GROUP",            joinColumns = @JoinColumn(name = "groupid"),            inverseJoinColumns = @JoinColumn(name = "userid"))  private List<User> users;}

Solution suggested by @PedroKowalski should work too, but then you'll have to keep a reference to Group entity in your User entity which is not always possible.

To have the same annotations like in your diagram you can do this in your User class:

@ManyToMany(fetch = FetchType.LAZY)@JoinTable(name = "USER_GROUP",            joinColumns = { @JoinColumn(name = "userid") },            inverseJoinColumns = { @JoinColumn(name = "groupid") })private List<Group> grups;

in your group class

@ManyToMany(fetch = FetchType.LAZY)@JoinTable(name = "USER_GROUP",            joinColumns = { @JoinColumn(name = "groupid") },            inverseJoinColumns = { @JoinColumn(name = "userid") })private List<User> users;