ManyToMany

@Entity
@Table(name = "usuario")
public class Usuario implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @Column(name = "id_usuario")
    private Integer idUsuario;

    @Column(name = "ds_login")
    private String dsLogin;

    @Column(name = "ds_senha")
    private String dsSenha;

    @Column(name = "nm_usuario")
    private String nmUsuario;

    @Column(name = "tp_situacao")
    private String tpSituacao;
    
    @ManyToMany
    @JoinTable(name="permissao", 
    		joinColumns={@JoinColumn(name="id_usuario")},
    		inverseJoinColumns={@JoinColumn(name="id_papel")})
    private List<Papel> listaPapel;

@Entity
@Table(name = "papel")
public class Papel implements Serializable {
    
    private static final long serialVersionUID = 1L;
    
    public Papel()
    {
    	idPapel = 1;
    	dsPapel = "master";
    }
    
    @Id
    @Column(name = "id_papel")
    private Integer idPapel;
    
    @Column(name = "ds_papel")
    private String dsPapel;
    
    @ManyToMany(mappedBy="listaPapel")
    private List<Usuario> listaUsuario;

Usuario user = new Usuario();
			
			user.setIdUsuario(1);
			user.setNmUsuario("Cristian");
			user.setDsLogin("cristian");
			user.setDsSenha("cris");
			user.setTpSituacao("1");
			user.setListaPapel(new ArrayList<Papel>());
			user.getListaPapel().add(new Papel());
			
			dao.salvar(user);

org.hibernate.exception.ConstraintViolationException: could not insert collection: [com.consisanet.slu.entity.Usuario.listaPapel#1]
	at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:96)
	at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
	at org.hibernate.persister.collection.AbstractCollectionPersister.recreate(AbstractCollectionPersister.java:1243)
	at org.hibernate.action.CollectionRecreateAction.execute(CollectionRecreateAction.java:58)
	at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:273)
	at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:265)
	at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:188)
	at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)
	at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)
	at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1216)
	at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:383)
	at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:133)
	at com.consisa.global.consisafpj.hibernate.HibernateTier.commitTrans(HibernateTier.java:258)
	at com.consisa.global.consisafpj.dao.GenericDAO.commitTrans(GenericDAO.java:190)
	at com.consisanet.slu.test.TesteAndre.main(TesteAndre.java:40)
Caused by: java.sql.BatchUpdateException: Entrada em lote 0 insert into permissao (id_usuario, id_papel) values ('1', '1') foi abortada. Chame getNextException para ver a causa.
	at org.postgresql.jdbc2.AbstractJdbc2Statement$BatchResultHandler.handleError(AbstractJdbc2Statement.java:2598)
	at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1836)
	at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:407)
	at org.postgresql.jdbc2.AbstractJdbc2Statement.executeBatch(AbstractJdbc2Statement.java:2737)
	at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:70)
	at org.hibernate.jdbc.BatchingBatcher.addToBatch(BatchingBatcher.java:56)
	at org.hibernate.persister.collection.AbstractCollectionPersister.recreate(AbstractCollectionPersister.java:1206)
	... 12 more

Caused by: java.sql.BatchUpdateException: Entrada em lote 0 insert into permissao (id_usuario, id_papel) values ('1', '1') foi abortada. Chame getNextException para ver a causa.