概括的描述一下Spring注册流程

Spring经过大神们的构思、编码，日积月累而来，所以，对其代码的理解也不是一朝一夕就能快速完成的。源码学习是枯燥的，需要坚持！坚持！坚持！当然也需要技巧，第一遍学习的时候，不用关注全部细节，不重要的代码可以先忽略掉，达到理解大体的架子及流程，避免第一次就陷入某个坑里出不来。第二遍针对某个流程更深入的、有针对性的去分析学习，当然遇到某个实在过不去的坎可以标记，后面再思考，毕竟是别人设计的，有些不是那么容易理解，可以使用google，次数多了，总会有收获！

概括的描述一下Spring背后的操作，解析applicationgContext.xml，将xml中定义的bean(如loginService和loginResource)解析成Spring内部的BeanDefinition，并以beanName(如loginService)为key，BeanDefinition(如loginService相应的BeanDefinition)为value存储到DefaultListableBeanFactory中的beanDefinitionMap(其实就是一个ConcurrentHashMap)中，同时将beanName存入beanDefinitionNames(List类型)中，然后遍历beanDefinitionNames中的beanName，进行bean的实例化并填充属性，在实例化的过程中，如果有依赖没有被实例化将先实例化其依赖，然后实例化本身，实例化完成后将实例存入单例bean的缓存中，当调用getBean方法时，到单例bean的缓存中查找，如果找到并经过转换后返回这个实例(如LoginResource的实例)，之后就可以直接使用了。

上边提到在Spring容器启动的过程中，会将Bean解析成Spring内部的BeanDefinition结构，BeanDefinition的内部结构。直接看BeanDefinition源码

1. public interface BeanDefinition extends AttributeAccessor, BeanMetadataElement {
2. /**
3. * Scope identifier for the standard singleton scope: "singleton".
4. * <p>Note that extended bean factories might support further scopes.
5. */
6. String SCOPE_SINGLETON = ConfigurableBeanFactory.SCOPE_SINGLETON;
7. /**
8. * Scope identifier for the standard prototype scope: "prototype".
9. * <p>Note that extended bean factories might support further scopes.
10. */
11. String SCOPE_PROTOTYPE = ConfigurableBeanFactory.SCOPE_PROTOTYPE;
12. /**
13. * Role hint indicating that a {@code BeanDefinition} is a major part
14. * of the application. Typically corresponds to a user-defined bean.
15. */
16. int ROLE_APPLICATION = 0;
17. /**
18. * Role hint indicating that a {@code BeanDefinition} is a supporting
19. * part of some larger configuration, typically an outer
20. * {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
21. * {@code SUPPORT} beans are considered important enough to be aware
22. * of when looking more closely at a particular
23. * {@link org.springframework.beans.factory.parsing.ComponentDefinition},
24. * but not when looking at the overall configuration of an application.
25. */
26. int ROLE_SUPPORT = 1;
27. /**
28. * Role hint indicating that a {@code BeanDefinition} is providing an
29. * entirely background role and has no relevance to the end-user. This hint is
30. * used when registering beans that are completely part of the internal workings
31. * of a {@link org.springframework.beans.factory.parsing.ComponentDefinition}.
32. */
33. int ROLE_INFRASTRUCTURE = 2;
34. /**
35. * Return the name of the parent definition of this bean definition, if any.
36. */
37. String getParentName();
38. /**
39. * Set the name of the parent definition of this bean definition, if any.
40. */
41. void setParentName(String parentName);
42. /**
43. * Return the current bean class name of this bean definition.
44. * <p>Note that this does not have to be the actual class name used at runtime, in
45. * case of a child definition overriding/inheriting the class name from its parent.
46. * Hence, do <i>not</i> consider this to be the definitive bean type at runtime but
47. * rather only use it for parsing purposes at the individual bean definition level.
48. */
49. String getBeanClassName();
50. /**
51. * Override the bean class name of this bean definition.
52. * <p>The class name can be modified during bean factory post-processing,
53. * typically replacing the original class name with a parsed variant of it.
54. */
55. void setBeanClassName(String beanClassName);
56. /**
57. * Return the factory bean name, if any.
58. */
59. String getFactoryBeanName();
60. /**
61. * Specify the factory bean to use, if any.
62. */
63. void setFactoryBeanName(String factoryBeanName);
64. /**
65. * Return a factory method, if any.
66. */
67. String getFactoryMethodName();
68. /**
69. * Specify a factory method, if any. This method will be invoked with
70. * constructor arguments, or with no arguments if none are specified.
71. * The method will be invoked on the specified factory bean, if any,
72. * or otherwise as a static method on the local bean class.
73. * @param factoryMethodName static factory method name,
74. * or {@code null} if normal constructor creation should be used
75. */
76. void setFactoryMethodName(String factoryMethodName);
77. /**
78. * Return the name of the current target scope for this bean,
79. * or {@code null} if not known yet.
80. */
81. String getScope();
82. /**
83. * Override the target scope of this bean, specifying a new scope name.
84. */
85. void setScope(String scope);
86. /**
87. * Return whether this bean should be lazily initialized, i.e. not
88. * eagerly instantiated on startup. Only applicable to a singleton bean.
89. */
90. boolean isLazyInit();
91. /**
92. * Set whether this bean should be lazily initialized.
93. * <p>If {@code false}, the bean will get instantiated on startup by bean
94. * factories that perform eager initialization of singletons.
95. */
96. void setLazyInit(boolean lazyInit);
97. /**
98. * Return the bean names that this bean depends on.
99. */
100. String[] getDependsOn();
101. /**
102. * Set the names of the beans that this bean depends on being initialized.
103. * The bean factory will guarantee that these beans get initialized first.
104. */
105. void setDependsOn(String... dependsOn);
106. /**
107. * Return whether this bean is a candidate for getting autowired into some other bean.
108. */
109. boolean isAutowireCandidate();
110. /**
111. * Set whether this bean is a candidate for getting autowired into some other bean.
112. */
113. void setAutowireCandidate(boolean autowireCandidate);
114. /**
115. * Return whether this bean is a primary autowire candidate.
116. * If this value is true for exactly one bean among multiple
117. * matching candidates, it will serve as a tie-breaker.
118. */
119. boolean isPrimary();
120. /**
121. * Set whether this bean is a primary autowire candidate.
122. * <p>If this value is true for exactly one bean among multiple
123. * matching candidates, it will serve as a tie-breaker.
124. */
125. void setPrimary(boolean primary);
126. /**
127. * Return the constructor argument values for this bean.
128. * <p>The returned instance can be modified during bean factory post-processing.
129. * @return the ConstructorArgumentValues object (never {@code null})
130. */
131. ConstructorArgumentValues getConstructorArgumentValues();
132. /**
133. * Return the property values to be applied to a new instance of the bean.
134. * <p>The returned instance can be modified during bean factory post-processing.
135. * @return the MutablePropertyValues object (never {@code null})
136. */
137. MutablePropertyValues getPropertyValues();
138. /**
139. * Return whether this a <b>Singleton</b>, with a single, shared instance
140. * returned on all calls.
141. */
142. boolean isSingleton();
143. /**
144. * Return whether this a <b>Prototype</b>, with an independent instance
145. * returned for each call.
146. */
147. boolean isPrototype();
148. /**
149. * Return whether this bean is "abstract", that is, not meant to be instantiated.
150. */
151. boolean isAbstract();
152. /**
153. * Get the role hint for this {@code BeanDefinition}. The role hint
154. * provides the frameworks as well as tools with an indication of
155. * the role and importance of a particular {@code BeanDefinition}.
156. */
157. int getRole();
158. /**
159. * Return a human-readable description of this bean definition.
160. */
161. String getDescription();
162. /**
163. * Return a description of the resource that this bean definition
164. * came from (for the purpose of showing context in case of errors).
165. */
166. String getResourceDescription();
167. /**
168. * Return the originating BeanDefinition, or {@code null} if none.
169. * Allows for retrieving the decorated bean definition, if any.
170. * <p>Note that this method returns the immediate originator. Iterate through the
171. * originator chain to find the original BeanDefinition as defined by the user.
172. */
173. BeanDefinition getOriginatingBeanDefinition();
174. }

可以看到上面的很多属性和方法都很熟悉，例如类名、scope、属性、构造函数参数列表、依赖的bean、是否是单例类、是否是懒加载等，其实就是将Bean的定义信息存储到这个BeanDefinition相应的属性中，后面对Bean的操作就直接对BeanDefinition进行，例如拿到这个BeanDefinition后，可以根据里面的类名、构造函数、构造函数参数，使用反射进行对象创建。BeanDefinition是一个接口，是一个抽象的定义，实际使用的是其实现类，如ChildBeanDefinition、RootBeanDefinition、GenericBeanDefinition等。BeanDefinition继承了AttributeAccessor，说明它具有处理属性的能力；BeanDefinition继承了BeanMetadataElement，说明它可以持有Bean元数据元素，作用是可以持有XML文件的一个bean标签对应的Object。