List映射表
List列表是一个java集合存储在序列中的元素，并允许重复的元素。此接口的用户可以精确地控制，其中列表中的每个元素插入。用户可以通过他们的整数索引访问元素，并搜索列表中的元素。更正式地说，列表通常允许对元素e1和e2，使得e1.equals（e2），它们通常允许多个null元素，如果他们允许的null元素。
List列表被映射在该映射表中的元素，并将java.util.ArrayList中初始化。
定义RDBMS表：
考虑一个情况，需要员工记录存储在EMPLOYEE表，将有以下结构：
create table EMPLOYEE ( id INT NOT NULL auto_increment, first_name VARCHAR(20) default NULL, last_name VARCHAR(20) default NULL, salary INT default NULL, PRIMARY KEY (id) );
此外，假设每个员工都可以有一个或多个与他/她相关的证书。List集合映射需要在一个集合表的索引列。索引列定义集合中的元素的位置。因此，我们将存储证书的相关信息在一个单独的表，该表具有以下结构：
create table CERTIFICATE ( id INT NOT NULL auto_increment, certificate_name VARCHAR(30) default NULL, idx INT default NULL, employee_id INT default NULL, PRIMARY KEY (id) );
将有一个对多( one-to-many)的EMPLOYEE和证书对象之间的关系。
定义POJO类：
让我们实现一个POJO类员工将被用于保存与EMPLOYEE表中的对象和有证书的列表变量的集合。
import java.util.*;
public class Employee {
private int id;
private String firstName;
private String lastName;
private int salary;
private List certificates;
public Employee() {}
public Employee(String fname, String lname, int salary) {
this.firstName = fname;
this.lastName = lname;
this.salary = salary;
}
public int getId() {
return id;
}
public void setId( int id ) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName( String first_name ) {
this.firstName = first_name;
}
public String getLastName() {
return lastName;
}
public void setLastName( String last_name ) {
this.lastName = last_name;
}
public int getSalary() {
return salary;
}
public void setSalary( int salary ) {
this.salary = salary;
}
public List getCertificates() {
return certificates;
}
public void setCertificates( List certificates ) {
this.certificates = certificates;
}
}
我们需要相应的证书表定义另一个POJO类，这样的证书对象可以存储和检索到的证书表。
public class Certificate{
private int id;
private String name;
public Certificate() {}
public Certificate(String name) {
this.name = name;
}
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;
}
}
定义Hibernate映射文件：
让我们开发指定Hibernate如何定义的类映射到数据库表的映射文件。元素将被用来定义使用List集合的规则。表的索引是整数类型总是和使用
This class contains the employee detail.
This class contains the certificate records.
应该保存的映射文件中的格式
映射文档是具有
元素是可选元素，可以用来创建类的描述。
id元素内的
元素用于设置证书和Employee类之间的关系。我们使用cascade属性中
元素来告诉Hibernate来保存证书的对象，同时为Employee对象。 name属性被设置为在父类中定义的Listvariable，在我们的情况下，它是证书。
创建应用程序类：
最后，我们将创建应用程序类的main（）方法来运行应用程序。我们将使用这个应用程序，以节省一些员工的记录连同的证书，然后我们将申请CRUD操作上的记录。
import java.util.*;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class ManageEmployee {
private static SessionFactory factory;
public static void main(String[] args) {
try{
factory = new Configuration().configure().buildSessionFactory();
}catch (Throwable ex) {
System.err.println("Failed to create sessionFactory object." + ex);
throw new ExceptionInInitializerError(ex);
}
ManageEmployee ME = new ManageEmployee();
/* Let us have a set of certificates for the first employee */
ArrayList set1 = new ArrayList();
set1.add(new Certificate("MCA"));
set1.add(new Certificate("MBA"));
set1.add(new Certificate("PMP"));
/* Add employee records in the database */
Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, set1);
/* Another set of certificates for the second employee */
ArrayList set2 = new ArrayList();
set2.add(new Certificate("BCA"));
set2.add(new Certificate("BA"));
/* Add another employee record in the database */
Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, set2);
/* List down all the employees */
ME.listEmployees();
/* Update employee's salary records */
ME.updateEmployee(empID1, 5000);
/* Delete an employee from the database */
ME.deleteEmployee(empID2);
/* List down all the employees */
ME.listEmployees();
}
/* Method to add an employee record in the database */
public Integer addEmployee(String fname, String lname,
int salary, ArrayList cert){
Session session = factory.openSession();
Transaction tx = null;
Integer employeeID = null;
try{
tx = session.beginTransaction();
Employee employee = new Employee(fname, lname, salary);
employee.setCertificates(cert);
employeeID = (Integer) session.save(employee);
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
return employeeID;
}
/* Method to list all the employees detail */
public void listEmployees( ){
Session session = factory.openSession();
Transaction tx = null;
try{
tx = session.beginTransaction();
List employees = session.createQuery("FROM Employee").list();
for (Iterator iterator1 =
employees.iterator(); iterator1.hasNext();){
Employee employee = (Employee) iterator1.next();
System.out.print("First Name: " + employee.getFirstName());
System.out.print(" Last Name: " + employee.getLastName());
System.out.println(" Salary: " + employee.getSalary());
List certificates = employee.getCertificates();
for (Iterator iterator2 =
certificates.iterator(); iterator2.hasNext();){
Certificate certName = (Certificate) iterator2.next();
System.out.println("Certificate: " + certName.getName());
}
}
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
}
/* Method to update salary for an employee */
public void updateEmployee(Integer EmployeeID, int salary ){
Session session = factory.openSession();
Transaction tx = null;
try{
tx = session.beginTransaction();
Employee employee =
(Employee)session.get(Employee.class, EmployeeID);
employee.setSalary( salary );
session.update(employee);
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
}
/* Method to delete an employee from the records */
public void deleteEmployee(Integer EmployeeID){
Session session = factory.openSession();
Transaction tx = null;
try{
tx = session.beginTransaction();
Employee employee =
(Employee)session.get(Employee.class, EmployeeID);
session.delete(employee);
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
}
}
编译和执行：
下面是步骤来编译并运行上述应用程序。请确保您已在进行的编译和执行之前，适当地设置PATH和CLASSPATH。
- 创建hibernate.cfg.xml配置文件中配置章节解释。
- 创建Employee.hbm.xml映射文件，如上图所示。
- 创建Employee.java源文件，如上图所示，并编译它.
- 创建Certificate.java源文件，如上图所示，并编译它。
- 创建ManageEmployee.java源文件，如上图所示，并编译它。
- 执行ManageEmployee二进制文件来运行程序。
会在屏幕上获得以下结果，并同时记录会在员工和证书表被创建。可以看到证书已排序顺序相反。可以通过改变映射文件试试，只需设置sort="natural"和执行程序，并比较结果。
$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........ First Name: Manoj Last Name: Kumar Salary: 4000 Certificate: MCA Certificate: MBA Certificate: PMP First Name: Dilip Last Name: Kumar Salary: 3000 Certificate: BCA Certificate: BA First Name: Manoj Last Name: Kumar Salary: 5000 Certificate: MCA Certificate: MBA Certificate: PMP
如果检查员工和证书表，就应该记录下了：
mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+ | id | first_name | last_name | salary | +----+------------+-----------+--------+ | 51 | Manoj | Kumar | 5000 | +----+------------+-----------+--------+ 1 row in set (0.00 sec)
mysql> select * from CERTIFICATE;
+----+------------------+------+-------------+ | id | certificate_name | idx | employee_id | +----+------------------+------+-------------+ | 6 | MCA | 0 | 51 | | 7 | MBA | 1 | 51 | | 8 | PMP | 2 | 51 | +----+------------------+------+-------------+ 3 rows in set (0.00 sec)
或者，您也可以映射Java数组，而不是一个列表。一个数组的映射几乎是相同的前面的例子，除了与不同的元素和属性名称（
Bag映射
Bag是一个java集合存储元素无需关心顺序，但允许列表中的重复元素。Bag是在列表中的对象的随机分组。
Collection集合被映射在该映射表中的
下面的示例中RDBMS表和POJO类依然使用上面定义好的。
定义Hibernate映射文件：
让我们开发指示Hibernate如何定义的类映射到数据库表的映射文件。
This class contains the employee detail. This class contains the certificate records.
应该保存的映射文件中的格式
映射文档是具有
元素是可选元素，可以用来创建类的描述。
id元素内的
创建应用程序类：
最后，我们将创建应用程序类的main（）方法来运行应用程序。我们将使用这个应用程序，以节省一些员工的记录连同的证书，然后我们将申请CRUD操作上的记录。
import java.util.*;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class ManageEmployee {
private static SessionFactory factory;
public static void main(String[] args) {
try{
factory = new Configuration().configure().buildSessionFactory();
}catch (Throwable ex) {
System.err.println("Failed to create sessionFactory object." + ex);
throw new ExceptionInInitializerError(ex);
}
ManageEmployee ME = new ManageEmployee();
/* Let us have a set of certificates for the first employee */
ArrayList set1 = new ArrayList();
set1.add(new Certificate("MCA"));
set1.add(new Certificate("MBA"));
set1.add(new Certificate("PMP"));
/* Add employee records in the database */
Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, set1);
/* Another set of certificates for the second employee */
ArrayList set2 = new ArrayList();
set2.add(new Certificate("BCA"));
set2.add(new Certificate("BA"));
/* Add another employee record in the database */
Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, set2);
/* List down all the employees */
ME.listEmployees();
/* Update employee's salary records */
ME.updateEmployee(empID1, 5000);
/* Delete an employee from the database */
ME.deleteEmployee(empID2);
/* List down all the employees */
ME.listEmployees();
}
/* Method to add an employee record in the database */
public Integer addEmployee(String fname, String lname,
int salary, ArrayList cert){
Session session = factory.openSession();
Transaction tx = null;
Integer employeeID = null;
try{
tx = session.beginTransaction();
Employee employee = new Employee(fname, lname, salary);
employee.setCertificates(cert);
employeeID = (Integer) session.save(employee);
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
return employeeID;
}
/* Method to list all the employees detail */
public void listEmployees( ){
Session session = factory.openSession();
Transaction tx = null;
try{
tx = session.beginTransaction();
List employees = session.createQuery("FROM Employee").list();
for (Iterator iterator1 =
employees.iterator(); iterator1.hasNext();){
Employee employee = (Employee) iterator1.next();
System.out.print("First Name: " + employee.getFirstName());
System.out.print(" Last Name: " + employee.getLastName());
System.out.println(" Salary: " + employee.getSalary());
Collection certificates = employee.getCertificates();
for (Iterator iterator2 =
certificates.iterator(); iterator2.hasNext();){
Certificate certName = (Certificate) iterator2.next();
System.out.println("Certificate: " + certName.getName());
}
}
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
}
/* Method to update salary for an employee */
public void updateEmployee(Integer EmployeeID, int salary ){
Session session = factory.openSession();
Transaction tx = null;
try{
tx = session.beginTransaction();
Employee employee =
(Employee)session.get(Employee.class, EmployeeID);
employee.setSalary( salary );
session.update(employee);
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
}
/* Method to delete an employee from the records */
public void deleteEmployee(Integer EmployeeID){
Session session = factory.openSession();
Transaction tx = null;
try{
tx = session.beginTransaction();
Employee employee =
(Employee)session.get(Employee.class, EmployeeID);
session.delete(employee);
tx.commit();
}catch (HibernateException e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
}
}
编译和执行：
会在屏幕上获得以下结果，并同时记录会在员工和证书表被创建。可以看到证书已排序顺序相反。可以通过改变映射文件试试，只需设置sort="natural"和执行程序，并比较结果。
$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........ First Name: Manoj Last Name: Kumar Salary: 4000 Certificate: MCA Certificate: MBA Certificate: PMP First Name: Dilip Last Name: Kumar Salary: 3000 Certificate: BCA Certificate: BA First Name: Manoj Last Name: Kumar Salary: 5000 Certificate: MCA Certificate: MBA Certificate: PMP
如果检查员工和证书表，就应该记录下了：
mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+ | id | first_name | last_name | salary | +----+------------+-----------+--------+ | 53 | Manoj | Kumar | 5000 | +----+------------+-----------+--------+ 1 row in set (0.00 sec)
mysql> select * from CERTIFICATE;
+----+------------------+-------------+ | id | certificate_name | employee_id | +----+------------------+-------------+ | 11 | MCA | 53 | | 12 | MBA | 53 | | 13 | PMP | 53 | +----+------------------+-------------+ 3 rows in set (0.00 sec)