春季创建相同接口的bean

Question

Consider a package which many classes all implement an interface Policy . The Policy has one method canAccess . There are 100+ policies like MenNotAllowedPolicy , ChiledNotAllowedPolicy ,... which all implement Policy

A property file describe which policies are applied to which service, for example:

BarrowBook=MenNotAllowedPolicy
BarrowMovie=MenNotAllowedPolicy,ChiledNotAllowedPolicy

To uses these polices there is a simple loop, which gets a service name an person, loop the property file and run the polices for persons. The main part of this code is:

public canPersonAccessService(aPerson , aService){
  //the listPolicy will be read from property file
  for(String policyClassName: listPolicy){        
      Class<?> clazz = Class.forName("foo.bar.Policies"+ policyClassName);
      Policy policy = (policy) clazz.newInstance();
      policy.canAccess(aPerson);
  }
}

Although Ii can make better by catching the Policy classes but I wonder if it is possible to do it easier with Spring ?! I decided a HashMap with ClassName as a key and the class instance as value, but how can I create it ?!

This a mimic of my problem :)

Answer 1

Define an interface called Policy as base interface for all policy implementations

interface Policy {
    boolean canAccess(User u);
}

Have one Spring Bean for each of the policy implementations - make sure you name the bean in @Component and ensure that it matches the name used in your properties file

@Component("MenNotAllowedPolicy")
public static class MenNotAllowedPolicy implements Policy {
    public boolean canAcces(User u) {
      ...
    }
}

Make the class that checks the policies also a Spring Bean, and have Spring ApplicationContext autowired in it

@Component
public static class PolicyChecker {
    ...
    @Autowired
    private ApplicationContext appContext;
    ...
    public boolean canPersonAccessService(User person, ....) {
       for(String policyName: listPolicy) { 
          Policy policy = appContext.getBean(policyName, Policy.class);
        ....
        policy.canAccess(person);
        ....
      }
    }
}

We look up policy by the its bean name, while also ensuring that bean implements Policy interface as indicated by second parameter of getBean method.

Hope this helps!