初用JPA @Embedded和@Emdeddable注解，对其用法不理解，哪位详细解释下注解双方是怎样关联起来的？
以某网志中两个class为例：
- Java code
File: Address.javaimport javax.persistence.Column;import javax.persistence.Embeddable;@Embeddablepublic class Address { private String street; private String city; private String state; @Column(name="ZIP_CODE") private String zip; public String getStreet() { return street; } public void setStreet(String address) { this.street = address; } public String getCity() { return city; } public void setCity(String city) { this.city = city; } public String getState() { return state; } public void setState(String state) { this.state = state; } public String getZip() { return zip; } public void setZip(String zip) { this.zip = zip; } public String toString() { return "Address street: " + getStreet() + ", city: " + getCity() + ", state: " + getState() + ", zip: " + getZip(); }}File: Professor.javaimport javax.persistence.AttributeOverride;import javax.persistence.AttributeOverrides;import javax.persistence.Column;import javax.persistence.Embedded;import javax.persistence.Entity;import javax.persistence.Id;import javax.persistence.PrimaryKeyJoinColumn;import javax.persistence.SecondaryTable;import javax.persistence.Table;@Entity @Table(name="EMP") @SecondaryTable(name="EMP_ADDRESS", pkJoinColumns=@PrimaryKeyJoinColumn(name="EMP_ID"))public class Professor { @Id private int id; private String name; @Embedded @AttributeOverrides({ @AttributeOverride(name="street", column=@Column(table="EMP_ADDRESS")), @AttributeOverride(name="city", column=@Column(name="CITY", table="EMP_ADDRESS")), @AttributeOverride(name="state", column=@Column(name="STATE", table="EMP_ADDRESS")), @AttributeOverride(name="zip", column=@Column(name="ZIP_CODE", table="EMP_ADDRESS")) }) private Address address; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Address getAddress() { return address; } public void setAddress(Address address) { this.address = address; } public String toString() { return "Professor id: " + getId() + " name: " + getName() + " with " + getAddress(); }}这样Address和Professor在数据库中的表结构是怎样的呢？
------解决方案--------------------------------------------------------
EMP 表：
1. ID
2. NAME
EMP_ADDRESS 表：
1. EMP_ID
2. street
3. CITY
4. STATE
5. ZIP_CODE
这里除了两个不常用的 @Embedded, @Embeddable 外，还有个不常用的 @SecondaryTable
@SecondaryTable 表示一个 Entity 映射了两张表，当然了，用 @SecondaryTables 可以一个 Entity 映射成 N 张表。能这样映射的表需要有个条件，需要有外键引用字段才可以这样做。上面的例子中：
@SecondaryTable(name="EMP_ADDRESS", pkJoinColumns=@PrimaryKeyJoinColumn(name="EMP_ID"))
表示 EMP_ADDRESS 中的 EMP_ID 字段与 @Table(name="EMP") 中标注 @Id 的字段进行关联，由于 @PrimaryKeyJoinColumn 中没有 referencedColumnName 值，因此就默认与 EMP 的主键关联。
@Embeddable 表示这个非 Entity 类可以嵌在一个 Entity 类中作为属性存在。
@Embedded
@AttributeOverrides({
@AttributeOverride(name="street", column=@Column(table="EMP_ADDRESS")),
@AttributeOverride(name="city", column=@Column(name="CITY", table="EMP_ADDRESS")),