InjectorHelper


1   package jfun.yan.etc;
2   import jfun.yan.Binder;
3   import jfun.yan.Component;
4   import jfun.yan.Map2;
5   import jfun.yan.Monad;
6   import jfun.yan.Mutation;
7   import jfun.yan.util.Utils;
8   
9   /**
10   * This class provides helper functions to help dependency injections
11   * on objects not created by Yan.
12   * <p>
13   * @author Michelle Lei
14   *
15   */
16  public class InjectorHelper{
17    /**
18     * To create a Component object that will instantiate an object
19     * that implements a certain injector interface.
20     * <p>
21     * The injector interface should describe at least one method
22     * that expects one and only one parameter object. This method is responsible
23     * for injecting dependencies into this parameter object.
24     * </p>
25     * <p>
26     * The injection logic is encapsulated in a Binder object.
27     * </p>
28     * @param injector_itf The injector interface class.
29     * @param binder the Binder object encapsulating the dependency injection logic.
30     * @return the Component that instantiates the injector object.
31     */
32    public static Component getInjectorComponent(Class   injector_itf, Binder binder){
33      return Utils.asComponent(binder).factory(injector_itf);
34    }
35    
36    /**
37     * To create a Component that instantiates proxy.
38     * <p> 
39     * The proxy object is responsible for injecting dependencies
40     * into return values from the proxied methods.
41     * </p>
42     * <p>
43     * The dependency injection logic is described by the <i>binder</i> object.
44     * </p>
45     * <p>
46     * The instance instantiated by the <i>proxied</i> Component is proxied.
47     * </p>
48     * <p>
49     * Only the dependencies of return values of <i>injectee_type</i> are injected.
50     * </p>
51     * @param cloader The ClassLoader used by the dynamic proxy.
52     * @param itf the interface that the proxy implements.
53     * @param proxied the Component that instantiates the proxied object.
54     * @param injectee_type only return values of this type gets injected.
55     * @param binder this object encapsulates the injection logic.
56     * @return the new Component that instantiates the proxied object.
57     */
58    public static Component getProxyComponentReturningInjected(
59        final ClassLoader   cloader, final Class   itf,
60        Component proxied, final Class   injectee_type, Binder binder){
61      final Component mutation = getInjectorComponent(Mutation.class, binder);
62      final Component injected = Monad.map(proxied, mutation, new Map2(){
63        public Object   map(Object   proxied, Object   mut){
64          return InjectingProxy.getInjectingProxy(cloader, itf, 
65              proxied, injectee_type, (Mutation)mut);
66        }
67      });
68      return injected;
69    }
70    /**
71     * To create a Component that instantiates proxy.
72     * <p> 
73     * The proxy object is responsible for injecting dependencies
74     * into return values from the proxied methods.
75     * </p>
76     * <p>
77     * The dependency injection logic is described by the <i>binder</i> object.
78     * </p>
79     * <p>
80     * The instance instantiated by the <i>proxied</i> Component is proxied.
81     * </p>
82     * <p>
83     * Only the dependencies of return values of <i>injectee_type</i> are injected.
84     * </p>
85     * <p>
86     * The ClassLoader that loads the proxied instance is used to load the dynamic proxy.
87     * </p>
88     * @param itf the interface that the proxy implements.
89     * @param proxied the Component that instantiates the proxied object.
90     * @param injectee_type only return values of this type gets injected.
91     * @param binder this object encapsulates the injection logic.
92     * @return the new Component that instantiates the proxied object.
93     */
94    public static Component getProxyComponentReturningInjected(final Class   itf,
95        Component proxied, Class   injectee_type, Binder binder){
96      return getProxyComponentReturningInjected(injectee_type.getClassLoader(),
97          itf, proxied, injectee_type, binder);
98    }
99  }
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