java - How to create a composite primary with JPA (or Hibernate) annotations -

i got problem common problem , decided share resolution here.

the problem: have composite primary key in 1 of tables. need map jpa annotations.

my pojo1:

public class alarm {      @id     @column(name="alm_id")     private string id;      @column(name="alm_description")     private string desc;      @manytoone     @joincolumn(name = "alm_norm_id")     private alarm normalarm;       //getters , setters } 

my pojo2:

public class equipment {      @id     @column(name="equ_id")     private string id;      @column(name="equ_fixed_asset")     private string fixedasset;      @column(name="equ_service_tag")     private string servicetag;      //getters , setters  } 

so have table primary key equipment + alarm , need map that.

i didn't want create separate class handle primary key @idclass annotation. decided use @embeddedid , @embeddable annotations instead. result was:

@entity @table(name="alarm_counter") public class counter {      @embeddedid     private counterid id;      @column(name="aco_counter")     private int counter = 1;      @column(name="aco_last_reset")     private date resetdate;      public counter(){}      public counter(counterid id) {         super();         this.id = id;     }       //getters , setters      //...      //embeddable class handling primary key     @embeddable     public class counterid implements serializable{          /**          *           */         private static final long serialversionuid = 1l;          @manytoone         @joincolumn(name="aco_alarm_id")         private alarm alarm;          @manytoone         @joincolumn(name="aco_equipment_id")         private equipment equipment;          //default constructor         public counterid(){}          //constructor fields         public counterid(alarm alarm, equipment equipment) {             super();             this.alarm = alarm;             this.equipment = equipment;         }          //getters , setters     } } 

i still needed handle object persist hibernate. made following:

alarm al = alarmservice.get(alarm);                 //retrieve alarm object equipment eq = equipmentservice.get(equipment);     //retrieve equipment object  counter ct = new counter();                         //instantiates counter object counterid cid = ct.new counterid(alarm, equipment); //instantiates counterid object (composite primary key counter)  ct.setid(cid);                                      //sets primary key (counterid)