org.hibernate.AnnotationException: mappedBy reference an unknown target entity property: com.entity.annotations.House.district in com.entity.annotations.Street.houses
    at org.hibernate.cfg.annotations.CollectionBinder.bindStarToManySecondPass(CollectionBinder.java:578)
    at org.hibernate.cfg.annotations.CollectionBinder$1.secondPass(CollectionBinder.java:543)
    at org.hibernate.cfg.CollectionSecondPass.doSecondPass(CollectionSecondPass.java:66)
    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1177)
    at org.hibernate.cfg.AnnotationConfiguration.secondPassCompile(AnnotationConfiguration.java:329)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1333)
    at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:867)
    at com.test.Demo04.saveHouseInfo(Demo04.java:53)
    at com.test.Demo04.main(Demo04.java:18)
Exception in thread "main" java.lang.NullPointerException
    at com.test.Demo04.saveHouseInfo(Demo04.java:74)
    at com.test.Demo04.main(Demo04.java:18)

House.java

　 @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seq_house")
    @SequenceGenerator(name = "seq_house", sequenceName = "seq_house_id", allocationSize = 100, initialValue = 61)
    private int id;
    @Column(name = "title")
    private String title; // 标题
    @Column(name = "description")
    private String description; // 描述
    @Column(name = "price")
    private int price; // 出租价格
    @Column(name = "pubdate")
    private Date pubdate; // 发布时间
    @Column(name = "floorage")
    private int floorage; // 面积
    @Column(name = "contact")
    private String contact; // 联系人
    @Column(name = "user_id")
    private int user_id; // 用户编号
    @Column(name = "type_id")
    private int type_id; // 类型编号
    // private int street_id; // 街道编号
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "street_id")
    private Street streets;

Street.java

　 @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seq_street")
    @SequenceGenerator(name = "seq_street", sequenceName = "seq_street_id", allocationSize = 100, initialValue = 11)
    private int id;
    @Column(name = "name")
    private String name;

    @OneToMany(mappedBy = "district", cascade = { CascadeType.ALL })
    private List<House> houses = new ArrayList<House>();

错误的原因是： @OneToMany(mappedBy = "district", cascade = { CascadeType.ALL }) 这里面的   mappedBy中“district”写错了映射的对象