服务定位器模式
最后更新于:2022-03-27 00:25:46
服务定位器模式
服务定位器模式(Service Locator Pattern)用在我们想使用 JNDI 查询定位各种服务的时候。考虑到为某个服务查找 JNDI 的代价很高,服务定位器模式充分利用了缓存技术。在首次请求某个服务时,服务定位器在 JNDI 中查找服务,并缓存该服务对象。当再次请求相同的服务时,服务定位器会在它的缓存中查找,这样可以在很大程度上提高应用程序的性能。以下是这种设计模式的实体。
- 服务(Service) – 实际处理请求的服务。对这种服务的引用可以在 JNDI 服务器中查找到。
- Context / 初始的 Context – JNDI Context 带有对要查找的服务的引用。
- 服务定位器(Service Locator) – 服务定位器是通过 JNDI 查找和缓存服务来获取服务的单点接触。
- 缓存(Cache) – 缓存存储服务的引用,以便复用它们。
- 客户端(Client) – Client 是通过 ServiceLocator 调用服务的对象。
实现
我们将创建 ServiceLocator、InitialContext、Cache、Service 作为表示实体的各种对象。Service1 和 Service2 表示实体服务。
ServiceLocatorPatternDemo 类在这里是作为一个客户端,将使用 ServiceLocator 来演示服务定位器设计模式。
步骤 1
创建服务接口 Service。
Service.java
public interface Service {
public String getName();
public void execute();
}
public String getName();
public void execute();
}
步骤 2
创建实体服务。
Service1.java
public class Service1 implements Service {
public void execute(){
System.out.println("Executing Service1");
}
public String getName() {
return "Service1";
}
}
public void execute(){
System.out.println("Executing Service1");
}
@
Overridepublic String getName() {
return "Service1";
}
}
Service2.java
public class Service2 implements Service {
public void execute(){
System.out.println("Executing Service2");
}
public String getName() {
return "Service2";
}
}
public void execute(){
System.out.println("Executing Service2");
}
@
Overridepublic String getName() {
return "Service2";
}
}
步骤 3
为 JNDI 查询创建 InitialContext。
InitialContext.java
public class InitialContext {
public Object lookup(String jndiName){
if(jndiName.equalsIgnoreCase("SERVICE1")){
System.out.println("Looking up and creating a new Service1 object");
return new Service1();
}else if (jndiName.equalsIgnoreCase("SERVICE2")){
System.out.println("Looking up and creating a new Service2 object");
return new Service2();
}
return null;
}
}
public Object lookup(String jndiName){
if(jndiName.equalsIgnoreCase("SERVICE1")){
System.out.println("Looking up and creating a new Service1 object");
return new Service1();
}else if (jndiName.equalsIgnoreCase("SERVICE2")){
System.out.println("Looking up and creating a new Service2 object");
return new Service2();
}
return null;
}
}
步骤 4
创建缓存 Cache。
Cache.java
import java.util.ArrayList;
import java.util.List; public class Cache {
services = new ArrayList<Service>();
}
for (Service service : services) {
if(service.getName().equalsIgnoreCase(serviceName)){
System.out.println("Returning cached "+serviceName+" object");
return service;
}
}
return null;
}
boolean exists = false;
for (Service service : services) {
if(service.getName().equalsIgnoreCase(newService.getName())){
exists = true;
}
}
if(!exists){
services.add(newService);
}
}
}
import java.util.List; public class Cache {
private List<Service> services;
public Cache(){
services = new ArrayList<Service>();
}
public Service getService(String serviceName){
for (Service service : services) {
if(service.getName().equalsIgnoreCase(serviceName)){
System.out.println("Returning cached "+serviceName+" object");
return service;
}
}
return null;
}
public void addService(Service newService){
boolean exists = false;
for (Service service : services) {
if(service.getName().equalsIgnoreCase(newService.getName())){
exists = true;
}
}
if(!exists){
services.add(newService);
}
}
}
步骤 5
创建服务定位器。
ServiceLocator.java
public class ServiceLocator {
private static Cache cache;
cache = new Cache();
}
return service;
}
Service service1 = (Service)context.lookup(jndiName);
cache.addService(service1);
return service1;
}
}
private static Cache cache;
static {
cache = new Cache();
}
public static Service getService(String jndiName){
Service service = cache.getService(jndiName);
if(service != null){
return service;
}
InitialContext context = new InitialContext();
Service service1 = (Service)context.lookup(jndiName);
cache.addService(service1);
return service1;
}
}
步骤 6
使用 ServiceLocator 来演示服务定位器设计模式。
ServiceLocatorPatternDemo.java
public class ServiceLocatorPatternDemo {
public static void main(String[] args) {
Service service = ServiceLocator.getService("Service1");
service.execute();
service = ServiceLocator.getService("Service2");
service.execute();
service = ServiceLocator.getService("Service1");
service.execute();
service = ServiceLocator.getService("Service2");
service.execute();
}
}
public static void main(String[] args) {
Service service = ServiceLocator.getService("Service1");
service.execute();
service = ServiceLocator.getService("Service2");
service.execute();
service = ServiceLocator.getService("Service1");
service.execute();
service = ServiceLocator.getService("Service2");
service.execute();
}
}
步骤 7
执行程序,输出结果:
Looking up and creating a new Service1 object Executing Service1 Looking up and creating a new Service2 object Executing Service2 Returning cached Service1 object Executing Service1 Returning cached Service2 object Executing Service2