詳解Java的Hibernat框架中的Map映照與SortedMap映照。本站提示廣大學習愛好者：（詳解Java的Hibernat框架中的Map映照與SortedMap映照）文章只能為提供參考，不一定能成為您想要的結果。以下是詳解Java的Hibernat框架中的Map映照與SortedMap映照正文
Map映照
Map映照是一個java聚集存儲在鍵 - 值對的元素，而且不許可在列表中反復的元素。 Map接口供給三種collection視圖，許可Map內容看做是一組鍵-值聚集，或許設置鍵 - 值映照關系。
Map被映照到映照表中一個<map>元素和無序的地圖可以在java.util.HashMap中被初始化。
界說RDBMS表：
斟酌一個情形，我們須要員工記載存儲在EMPLOYEE表，將有以下構造：
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) );
另外，假定每一個員工都可以有一個或多個與他/她相干的證書。我們將存儲證書的相干信息在一個零丁的表，該表具有以下構造：
create table CERTIFICATE ( id INT NOT NULL auto_increment, certificate_type VARCHAR(40) default NULL, certificate_name VARCHAR(30) default NULL, employee_id INT default NULL, PRIMARY KEY (id) );
有一個對多（one-to-many ）的關系在EMPLOYEE和證書對象之間。
界說POJO類：
讓我們完成一個POJO類員工將被用於保留與EMPLOYEE表中的對象和有證書的列表變量的聚集。
import java.util.*;
public class Employee {
private int id;
private String firstName;
private String lastName;
private int salary;
private Map 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 Map getCertificates() {
return certificates;
}
public void setCertificates( Map certificates ) {
this.certificates = certificates;
}
}
我們須要響應的證書表界說另外一個POJO類，如許的證書對象可以存儲和檢索到的證書表。
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;
}
}
界說Hibernate映照文件：
讓我們開辟指導Hibernate若何界說的類映照到數據庫表的映照文件。<map>元素將被用於界說所應用的映照的規矩。
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Employee" table="EMPLOYEE">
<meta attribute="class-description">
This class contains the employee detail.
</meta>
<id name="id" type="int" column="id">
<generator class="native"/>
</id>
<map name="certificates" cascade="all">
<key column="employee_id"/>
<index column="certificate_type" type="string"/>
<one-to-many class="Certificate"/>
</map>
<property name="firstName" column="first_name" type="string"/>
<property name="lastName" column="last_name" type="string"/>
<property name="salary" column="salary" type="int"/>
</class>
<class name="Certificate" table="CERTIFICATE">
<meta attribute="class-description">
This class contains the certificate records.
</meta>
<id name="id" type="int" column="id">
<generator class="native"/>
</id>
<property name="name" column="certificate_name" type="string"/>
</class>
</hibernate-mapping>
應當保留的映照文件中的格局<classname>.hbm.xml。我們保留映照文件中的文件Employee.hbm.xml。曾經熟習了年夜部門的映照細節，但讓我們再次看映照文件中的一切元素：
映照文檔是具有<hibernate-mapping>為對應於每個類包括2個<class>元素的根元素的XML文檔。
<class>元素被用於界說數據庫表從一個Java類特定的映照。 Java類名指定應用class元素的name屬性和應用表屬性數據庫表名指定。
<meta>元素是可選元素，可以用來創立類的描寫。
<id>元素映照在類中的獨一ID屬性到數據庫表的主鍵。 id元素的name屬性是指屬性的類和column屬性是指在數據庫表中的列。 type屬性保留了Hibernate映照類型，這類類型的映照將會從Java轉換為SQL數據類型。
id元素內的<generator>元素被用來主動生成的主鍵值。將生成元素的class屬性設置為原產於讓Hibernate拿起不管是identity，sequence或許hilo中的算法來創立主鍵依據底層數據庫的支撐才能。
<property>元素用於一個Java類的屬性映照到數據庫表中的列。元素的name屬性是指屬性的類和column屬性是指在數據庫表中的列。 type屬性保留了Hibernate映照類型，這類類型的映照將會從Java轉換為SQL數據類型。
<map>元素用於設置證書和Employee類之間的關系。我們應用cascade屬性的<map>元從來告知Hibernate來保留證書的對象，同時為Employee對象。 name屬性設置為界說Mapvariable在父類中，在我們的案例中是證書。
<index>的元素用於表現鍵/值對地圖的症結部位。該鍵將應用一個字符串類型的存儲在列certificate_type。
<key>元素是包括外鍵的父對象，即在證書表中的列。表EMPLOYEE。
<one-to-many>元素表現一個Employee對象觸及到許多證書的對象，並是以，證書對象必需有與Employee父類有關。可以依據須要應用<one-to-one>，<many-to-one>或<many-to-many>這個元素。
創立運用法式類：
最初，創立運用法式類的main（）辦法來運轉運用法式。應用這個運用法式來保留員工記載地連同證書列表，然後在運用上履行CRUD操作上的記載。
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 */
HashMap set = new HashMap();
set.put("ComputerScience", new Certificate("MCA"));
set.put("BusinessManagement", new Certificate("MBA"));
set.put("ProjectManagement", new Certificate("PMP"));
/* Add employee records in the database */
Integer empID = ME.addEmployee("Manoj", "Kumar", 4000, set);
/* List down all the employees */
ME.listEmployees();
/* Update employee's salary records */
ME.updateEmployee(empID, 5000);
/* 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, HashMap 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());
Map ec = employee.getCertificates();
System.out.println("Certificate: " +
(((Certificate)ec.get("ComputerScience")).getName()));
System.out.println("Certificate: " +
(((Certificate)ec.get("BusinessManagement")).getName()));
System.out.println("Certificate: " +
(((Certificate)ec.get("ProjectManagement")).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();
}
}
}
編譯和履行：
上面是步調來編譯並運轉上述運用法式。請確保您已在停止的編譯和履行之前，曾經恰當地設置PATH和CLASSPATH。
會在屏幕上取得以下成果，並同時創立記載在員工和證書表。
$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........
First Name: Manoj Last Name: Kumar Salary: 4000 Certificate: MCA Certificate: MBA Certificate: PMP First Name: Manoj Last Name: Kumar Salary: 5000 Certificate: MCA Certificate: MBA Certificate: PMP
假如檢討員工和證書表，就應當記載下了：
mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+ | id | first_name | last_name | salary | +----+------------+-----------+--------+ | 60 | Manoj | Kumar | 5000 | +----+------------+-----------+--------+ 1 row in set (0.00 sec)
mysql>select * from CERTIFICATE;
+----+--------------------+------------------+-------------+ | id | certificate_type | certificate_name | employee_id | +----+--------------------+------------------+-------------+ | 16 | ProjectManagement | PMP | 60 | | 17 | BusinessManagement | MBA | 60 | | 18 | ComputerScience | MCA | 60 | +----+--------------------+------------------+-------------+ 3 rows in set (0.00 sec)
SortedMap映照
SortedMap是存儲在鍵 - 值對的元素，並供給鍵的整體排序相似java的聚集作為映照。反復的元素未在映照不許可的。該映照是依據其鍵的天然次序停止排序，或許經由過程供給平日在有序映照的創立時光比擬。
SortedMap被映照在該映照表中的<map>元素和有序映照可以在java.util.TreeMap中被初始化。
我們仍然應用下面界說的RDBMS表和POJO類來說上面的例子：
界說Hibernate映照文件：
讓我們開辟指導Hibernate若何界說的類映照到數據庫表的映照文件。<map>元素將被用於界說所應用的映照的規矩。
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Employee" table="EMPLOYEE">
<meta attribute="class-description">
This class contains the employee detail.
</meta>
<id name="id" type="int" column="id">
<generator class="native"/>
</id>
<map name="certificates" cascade="all" sort="MyClass">
<key column="employee_id"/>
<index column="certificate_type" type="string"/>
<one-to-many class="Certificate"/>
</map>
<property name="firstName" column="first_name" type="string"/>
<property name="lastName" column="last_name" type="string"/>
<property name="salary" column="salary" type="int"/>
</class>
<class name="Certificate" table="CERTIFICATE">
<meta attribute="class-description">
This class contains the certificate records.
</meta>
<id name="id" type="int" column="id">
<generator class="native"/>
</id>
<property name="name" column="certificate_name" type="string"/>
</class>
</hibernate-mapping>
應當保留的映照文件中的格局<classname>.hbm.xml。我們保留映照文件Employee.hbm.xml。後面曾經熟習了年夜部門的映照細節，但讓我們再次看看映照文件中的一切元素：
映照文檔是具有<hibernate-mapping>對應於每個類包括2個<class>元素的根元素的XML文檔。
<class>元素被用於界說數據庫表從一個Java類特定的映照。 Java類名指定應用class元素的name屬性和應用表屬性數據庫表名指定。
<meta>元素是可選元素，可以用來創立類的描寫。
<id>元素映照在類中的獨一ID屬性到數據庫表的主鍵。 id元素的name屬性是指屬性的類和column屬性是指在數據庫表中的列。 type屬性保留了Hibernate映照類型，這類類型的映照將會從Java轉換為SQL數據類型。
id元素內的<generator>元素被用來主動生成的主鍵值。將生成元素的class屬性設置讓Hibernate對應於identity，sequence或許hilo中的算法來創立主鍵依據底層數據庫的支撐才能。
<property>元素用於一個Java類的屬性映照到數據庫表中的列。元素的name屬性是指屬性的類和column屬性是指在數據庫表中的列。 type屬性保留了Hibernate映照類型，這類類型的映照將會從Java轉換為SQL數據類型。
<map>元素用於設置證書和Employee類之間的關系。我們應用cascade屬性的<map>元從來告知Hibernate來保留證書的對象，同時為Employee對象。 name屬性被設置為在父類中的界說的SortedMap變量，在我們的情形下，它是證書。排序屬性可以設置為天然有天然排序，也能夠設置為自界說類完成為java.util.Comparator。我們曾經應用了一個類MyClass，它完成為java.util.Comparator改變證書類完成的排序次序。
<index>元素用於表現鍵/值對映照的鍵部門。該鍵將應用一個字符串類型的存儲在列certificate_type。
<key>元素是包括外鍵的父對象，即在證書表中的列。表EMPLOYEE。
<one-to-many>元素表現一個Employee對象觸及到許多證書的對象，並是以，證書對象必需有與Employee父有聯系關系。可以依據須要應用<one-to-one>，<many-to-one>或<many-to-many>這個元素。
假如應用sort="natural"，然後我們其實不須要創立一個零丁的類，由於證書類曾經完成了Comparable接口和hibernate會應用compareTo在證書類界說為比擬的SortedMap（）辦法。然則，我們應用的是在我們的映照文件自界說的比擬器類MyClass，所以我們必需創立這個類的基本上我們的排序算法。讓我們做降在映照上可用的按鍵排序。
import java.util.Comparator;
public class MyClass implements Comparator <String>{
public int compare(String o1, String o2) {
final int BEFORE = -1;
final int AFTER = 1;
/* To reverse the sorting order, multiple by -1 */
if (o2 == null) {
return BEFORE * -1;
}
Comparable thisCertificate = o1;
Comparable thatCertificate = o2;
if(thisCertificate == null) {
return AFTER * 1;
} else if(thatCertificate == null) {
return BEFORE * -1;
} else {
return thisCertificate.compareTo(thatCertificate) * -1;
}
}
}
最初，我們將創立運用法式類的main（）辦法來運轉運用法式。我們將應用這個運用法式，以節儉一些員工的記載地連同的證書，然後我們將提交CRUD操作下面的記載。
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 */
TreeMap set1 = new TreeMap();
set1.put("ComputerScience", new Certificate("MCA"));
set1.put("BusinessManagement", new Certificate("MBA"));
set1.put("ProjectManagement", 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 */
TreeMap set2 = new TreeMap();
set2.put("ComputerScience", new Certificate("MCA"));
set2.put("BusinessManagement", new Certificate("MBA"));
/* 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, TreeMap 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());
SortedMap<String, Certificate> map =
employee.getCertificates();
for(Map.Entry<String,Certificate> entry : map.entrySet()){
System.out.print("\tCertificate Type: " + entry.getKey());
System.out.println(", Name: " +
(entry.getValue()).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();
}
}
}
編譯和履行：
可以看到證書已排序次序相反。可以經由過程轉變映照文件嘗嘗，只需設置sort="natural"和履行法式，並比擬成果。
$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........ First Name: Manoj Last Name: Kumar Salary: 4000 Certificate Type: ProjectManagement, Name: PMP Certificate Type: ComputerScience, Name: MCA Certificate Type: BusinessManagement, Name: MBA First Name: Dilip Last Name: Kumar Salary: 3000 Certificate Type: ComputerScience, Name: MCA Certificate Type: BusinessManagement, Name: MBA First Name: Manoj Last Name: Kumar Salary: 5000 Certificate Type: ProjectManagement, Name: PMP Certificate Type: ComputerScience, Name: MCA Certificate Type: BusinessManagement, Name: MBA
假如檢討員工和證書表，就應當記載下了：
mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+ | id | first_name | last_name | salary | +----+------------+-----------+--------+ | 74 | Manoj | Kumar | 5000 | +----+------------+-----------+--------+ 1 row in set (0.00 sec)
mysql> select * from CERTIFICATE;
+----+--------------------+------------------+-------------+ | id | certificate_type | certificate_name | employee_id | +----+--------------------+------------------+-------------+ | 52 | BusinessManagement | MBA | 74 | | 53 | ComputerScience | MCA | 74 | | 54 | ProjectManagement | PMP | 74 | +----+--------------------+------------------+-------------+ 3 rows in set (0.00 sec)
