Spring-spring-components

docs/Spring/Spring5新特性/Spring-spring-components.md

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+# Spring5 新特性 - spring.components
+- Author: [HuiFer](https://github.com/huifer)
+- 源码阅读仓库: [huifer-spring](https://github.com/huifer/spring-framework-read)
+
+
+## 解析
+- 相关类: `org.springframework.context.index.CandidateComponentsIndexLoader`
+- 测试用例: `org.springframework.context.annotation.ClassPathScanningCandidateComponentProviderTests.defaultsWithIndex`,`org.springframework.context.index.CandidateComponentsIndexLoaderTests`
+- `CandidateComponentsIndexLoader`是怎么找出来的,全文搜索`spring.components`
+### 使用介绍
+- 下面是从`resources/example/scannable/spring.components`测试用例中复制过来的,从中可以发现等号左侧放的是我们写的组件,等号右边是属于什么组件
+```
+example.scannable.AutowiredQualifierFooService=example.scannable.FooService
+example.scannable.DefaultNamedComponent=org.springframework.stereotype.Component
+example.scannable.NamedComponent=org.springframework.stereotype.Component
+example.scannable.FooService=example.scannable.FooService
+example.scannable.FooServiceImpl=org.springframework.stereotype.Component,example.scannable.FooService
+example.scannable.ScopedProxyTestBean=example.scannable.FooService
+example.scannable.StubFooDao=org.springframework.stereotype.Component
+example.scannable.NamedStubDao=org.springframework.stereotype.Component
+example.scannable.ServiceInvocationCounter=org.springframework.stereotype.Component
+example.scannable.sub.BarComponent=org.springframework.stereotype.Component
+```
+
+### debug
+- 入口 `org.springframework.context.index.CandidateComponentsIndexLoader.loadIndex`
+```java
+    @Nullable
+    public static CandidateComponentsIndex loadIndex(@Nullable ClassLoader classLoader) {
+        ClassLoader classLoaderToUse = classLoader;
+        if (classLoaderToUse == null) {
+            classLoaderToUse = CandidateComponentsIndexLoader.class.getClassLoader();
+        }
+        return cache.computeIfAbsent(classLoaderToUse, CandidateComponentsIndexLoader::doLoadIndex);
+    }
+
+```
+```java
+    /**
+     * 解析  META-INF/spring.components 文件
+     * @param classLoader
+     * @return
+     */
+    @Nullable
+    private static CandidateComponentsIndex doLoadIndex(ClassLoader classLoader) {
+        if (shouldIgnoreIndex) {
+            return null;
+        }
+
+        try {
+            Enumeration<URL> urls = classLoader.getResources(COMPONENTS_RESOURCE_LOCATION);
+            if (!urls.hasMoreElements()) {
+                return null;
+            }
+            List<Properties> result = new ArrayList<>();
+            while (urls.hasMoreElements()) {
+                URL url = urls.nextElement();
+                // 读取META-INF/spring.components文件转换成map对象
+                Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
+                result.add(properties);
+            }
+            if (logger.isDebugEnabled()) {
+                logger.debug("Loaded " + result.size() + "] index(es)");
+            }
+            int totalCount = result.stream().mapToInt(Properties::size).sum();
+            // 查看CandidateComponentsIndex方法
+            return (totalCount > 0 ? new CandidateComponentsIndex(result) : null);
+        }
+        catch (IOException ex) {
+            throw new IllegalStateException("Unable to load indexes from location [" +
+                    COMPONENTS_RESOURCE_LOCATION + "]", ex);
+        }
+    }
+
+```
+
+```java
+  CandidateComponentsIndex(List<Properties> content) {
+        this.index = parseIndex(content);
+    }
+
+    /**
+     * 解析  MATE-INF\spring.components 转换成 map
+     *
+     * @param content
+     * @return
+     */
+    private static MultiValueMap<String, Entry> parseIndex(List<Properties> content) {
+        MultiValueMap<String, Entry> index = new LinkedMultiValueMap<>();
+        for (Properties entry : content) {
+            entry.forEach((type, values) -> {
+                String[] stereotypes = ((String) values).split(",");
+                for (String stereotype : stereotypes) {
+                    index.add(stereotype, new Entry((String) type));
+                }
+            });
+        }
+        return index;
+    }
+```
+
+
+
+
+
+![image-20200115105941265](/images/spring/image-20200115105941265.png)
+- 该类给`org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider.findCandidateComponents`提供了帮助
+
+```java
+    public Set<BeanDefinition> findCandidateComponents(String basePackage) {
+        // 扫描
+        /**
+         * if 测试用例: {@link org.springframework.context.annotation.ClassPathScanningCandidateComponentProviderTests#defaultsWithIndex()}
+         * 解析 spring.components文件
+         */
+        if (this.componentsIndex != null && indexSupportsIncludeFilters()) {
+            return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);
+        }
+        else {
+            return scanCandidateComponents(basePackage);
+        }
+    }
+
+```