Two foreign keys as primary key

you need an embeddable SocialProfileId like this :

@Embeddable
public class SocialProfileId implements Serializable {
    @Column(name = "user_id")
    private long userId;
    @Column(name = "social_network_id")
    private long socialNetworkId;
}

then, your SocialProfile entity will look like this :

@Entity
@Table(name = "social_profile")
public class SocialProfile implements java.io.Serializable {

    @EmbeddedId
    private SocialProfileId id;

    @ManyToOne
    @JoinColumn(name="user_id")
    public User getUser() {
        return user;
    }

    @ManyToOne
    @JoinColumn(name="social_network_id")
    public SocialNetwork getSocialNetwork() {
        return socialNetwork;
    }
}

EDIT sorry, i have mixed annotations on fields and methods on my answer ... never do that ! ;-)

In addition to what Pras has said, we can even move the @ManyToOne inside the @Embeddable class itself so SocialProfileId will look like, where you can clearly see in your Embedded class itself that it referencing another table

@Embeddable
public class SocialProfileId implements Serializable {

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User userId;


    @ManyToOne
    @JoinColumn(name = "social_network_id")
    private SocialNetwork socialNetworkId;

    public SocialProfileId(User userId, SocialNetwork socialNetworkId) {
        this.userId = userId;
        this.socialNetworkId = socialNetworkId;
    }

}

And your SocialProfile entity can simply have the embedded class and other fields like email and so on..

@Entity
@Table(name = "social_profile")
public class SocialProfile implements java.io.Serializable {

    @EmbeddedId
    private SocialProfileId id;

    @Column(name="email")
    private String email;
}