死磕源码系列【springboot之内部类解析processMemberClasses源码分析】

「爱情、让人受尽委屈。」 2022-12-27 07:25 120阅读 0赞

在将配置类解析为ConfigurationClass配置类时经常会遇到内部配置类的情况，遇到这种情况是如何解析的呢？本文对这一块进行一一解释；

##### ConfigurationClassParser\#processMemberClasses方法解析内部类 #####

//注册配置类成员嵌套类
    private void processMemberClasses(ConfigurationClass configClass, SourceClass sourceClass,
    			Predicate<String> filter) throws IOException { 
        //获取配置类的嵌套内部类
    		Collection<SourceClass> memberClasses = sourceClass.getMemberClasses();
        //如果嵌套内部类存在
    		if (!memberClasses.isEmpty()) { 
          //创建指定大小的内部类集合
    			List<SourceClass> candidates = new ArrayList<>(memberClasses.size());
    			for (SourceClass memberClass : memberClasses) { 
            //验证嵌套类是否是配置类（即：通过@Configuration、@Component、@Bean等注解标注）
    				if (ConfigurationClassUtils.isConfigurationCandidate(memberClass.getMetadata()) &&
    						!memberClass.getMetadata().getClassName().equals(configClass.getMetadata().getClassName())) { 
    					candidates.add(memberClass);
    				}
    			}
          //对嵌套内部类进行排序
    			OrderComparator.sort(candidates);
    			for (SourceClass candidate : candidates) { 
    				if (this.importStack.contains(configClass)) { 
    					this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));
    				}
    				else { 
    					this.importStack.push(configClass);
    					try { 
                //使用递归的方式将嵌套内部类当成普通的类来处理
    						processConfigurationClass(candidate.asConfigClass(configClass), filter);
    					}
    					finally { 
    						this.importStack.pop();
    					}
    				}
    			}
    		}
    	}

上述处理嵌套内部类还有一个比较核心的方法getMemberClasses，此方法获取配置类的嵌套内部类：

public Collection<SourceClass> getMemberClasses() throws IOException { 
    			Object sourceToProcess = this.source;
    			if (sourceToProcess instanceof Class) { 
    				Class<?> sourceClass = (Class<?>) sourceToProcess;
    				try { 
    					Class<?>[] declaredClasses = sourceClass.getDeclaredClasses();
    					List<SourceClass> members = new ArrayList<>(declaredClasses.length);
    					for (Class<?> declaredClass : declaredClasses) { 
    						members.add(asSourceClass(declaredClass, DEFAULT_EXCLUSION_FILTER));
    					}
    					return members;
    				}
    				catch (NoClassDefFoundError err) { 
    					// getDeclaredClasses() failed because of non-resolvable dependencies
    					// -> fall back to ASM below
    					sourceToProcess = metadataReaderFactory.getMetadataReader(sourceClass.getName());
    				}
    			}
    
    			// 基于ASM的解析，对于不可以解析的类也是安全的
          // 获取元数据读取器
    			MetadataReader sourceReader = (MetadataReader) sourceToProcess;
          // 获取配置类的嵌套内部类
    			String[] memberClassNames = sourceReader.getClassMetadata().getMemberClassNames();
          // 新建嵌套内部类集合
    			List<SourceClass> members = new ArrayList<>(memberClassNames.length);
    			for (String memberClassName : memberClassNames) { 
    				try { 
              // 将嵌套类转换成简单的包装类，并且经过默认过滤器的过滤
    					members.add(asSourceClass(memberClassName, DEFAULT_EXCLUSION_FILTER));
    				}
    				catch (IOException ex) { 
    					// Let's skip it if it's not resolvable - we're just looking for candidates
    					if (logger.isDebugEnabled()) { 
    						logger.debug("Failed to resolve member class [" + memberClassName +
    								"] - not considering it as a configuration class candidate");
    					}
    				}
    			}
    			return members;
    		}

上述方法只有下半部分是常使用的，上半部分基本很少使用，此处不再做一一解析；

GitHub地址：[https://github.com/mingyang66/spring-parent][https_github.com_mingyang66_spring-parent]

[https_github.com_mingyang66_spring-parent]: https://github.com/mingyang66/spring-parent