多个JPA选择查询

我有以下实体 @ManyToMany 两者之间的映射。

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

    /**
     * 
     */
    private static final long serialVersionUID = 5340562707217344212L;  
    @Id 
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long userId;
    private String userName;
    private String password;
    private String firstName;
    private String lastName;
    private String emailId;
    private Date createdDate;
    private Byte status;
    private Date lastModifiedDate;  
    @ManyToMany
    @JoinTable(name = "user_products_mapper",
               joinColumns = @JoinColumn(name = "user_id"),
               inverseJoinColumns = @JoinColumn(name = "product_id")
    )
    private List<Products> products = new ArrayList<Products>();

    public void addProducts(Products product){

        this.products.add(product);     
    }


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

    /**
     * 
     */
    private static final long serialVersionUID = 1895580713896126954L;
    @Id 
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long productId;
    private String productName;
    private String description;
    private double minBalance;


    public Long getProductId() {
        return this.productId;
    }

    public void setProductId(Long productId) {
        this.productId = productId;
    }

    public String getProductName() {
        return this.productName;
    }

    public void setProductName(String productName) {
        this.productName = productName;
    }

我的问题是:

1)如何根据 user id ?是指选择所订购的所有产品 用户ID ?

2)我在这上面挣扎,因为我没有任何映射 Product 侧向而上 User 一边。这是一个 unidirectional association

3)我将如何穿越 Products 通过 User entity ?