从零开始造Spring05---实现spring注解-1

前言

前几篇我们实现了配置的方式实现Bean的生成和注入，接下来我们将要通过注解的方式来实现这一过程。这是学习刘欣老师《从零开始造Spring》课程的学习笔记。在实现的过程中我们需要用到ASM的技术，具体可以参考ASM技术

实现思路

1. 读取XML文件
2. 对指定的package 进行扫描(scan) ,找到那些标记为@Component的类，创建BeanDefinition
   2.1 把一个package下面的class变成resource
   2.2 使用ASM读取Resource中的注解
   2.3 创建BeanDefinition
3. 通过BeanDefinition创建Bean实例，根据注解来注入。

具体实现

我们首先来了解下相关的注解，在此处，我们首先实现了两个最基本的注解@Component 注解和@Autowired 注解，注解的本质就是元数据。我们已@Autowired为例。

/**
 *
 * 注解本质上就是元数据，
 * @Target 标注注解的使用地方
 * @Documented 说注解就是一个元素，可以被文档化
 * Created by xiang.wei on 2018/7/14
 *
 */
 //构造器，字段，方法。
@Target({ElementType.CONSTRUCTOR, ElementType.FIELD, ElementType.METHOD, ElementType.ANNOTATION_TYPE})
//保留到运行时
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Autowired { /** * Declares whether the annotated dependency is required. * <p>Defaults to {@code true}. */ boolean required() default true;
}

  

 

  
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我们通过PackageResourceLoader类来将base-package 中配置的包下加载出对应的Resource
关键代码如下：

   public Resource[] getResources(String basePackage) throws IOException { Assert.notNull(basePackage, "basePackage must not be null"); String location = ClassUtils.convertClassNameToResourcePath(basePackage); ClassLoader cl = getClassLoader(); URL url = cl.getResource(location); File rootDir = new File(url.getFile()); Set<File> matchingFiles = retrieveMatchingFiles(rootDir); Resource[] result = new Resource[matchingFiles.size()]; int i = 0; for (File file : matchingFiles) { result[i++] = new FileSystemResource(file); } return result; }
  

 

  
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调试如下：

实现两个Visitor，实现SimpleMetaDataReader 这两步参考ASM在Spring中的应用

实现Scanner（对ASM的抽象）

如类图所示，我们抽象了一个MetadataReader接口,该接口依赖于AnnotationVisitor抽象类和ClassVisitor抽象类，而AnnotationAttributesReadingVisitor类和ClassMetadataReadingVisitor类又是这两个抽象类的实现。由此我们就完全隐藏了AnnotationAttributesReadingVisitor类和ClassMetadataReadingVisitor类
测试代码

public class MetadataReaderTest { @Test public void testGetMetadata() throws IOException { ClassPathResource resource = new ClassPathResource("com/jay/spring/service/v4/PetStoreService.class"); MetadataReader reader = new SimpleMetadataReader(resource); AnnotationMetadata amd = reader.getAnnotationMetadata(); String annotation = Component.class.getName(); Assert.assertTrue(amd.hasAnnotation(annotation)); AnnotationAttributes attributes = amd.getAnnotationAttributes(annotation); Assert.assertEquals("petStoreService", attributes.get("value")); Assert.assertFalse(amd.isAbstract()); Assert.assertFalse(amd.isFinal()); Assert.assertEquals("com.jay.spring.service.v4.PetStoreService", amd.getClassName()); }
}
  

 

  
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ClassMetadataReadingVisitor 类

 /** * @param version * @param access * @param name * @param signature * @param supername * @param interfaces * * * 这个涉及到了Java的字节码， 在Java字节码中，常量池结束之后， * 有两个字节表示访问标识(access_flags)， * 这个标识用于识别一些类或者接口层次的访问信息， * 例如这个Class是类或者接口，是否为public ,abstract ,final 等等 * 对类的处理，判断类的基本情况 * */ // @Override public void visit(int version, int access, String name, String signature, String supername, String[] interfaces) { this.className = ClassUtils.convertResourcePathToClassName(name); this.isInterface = ((access & Opcodes.ACC_INTERFACE) != 0); this.isAbstract = ((access & Opcodes.ACC_ABSTRACT) != 0); this.isFinal = ((access & Opcodes.ACC_FINAL) != 0); if (supername != null) { this.superClassName = ClassUtils.convertResourcePathToClassName(supername); } this.interfaces = new String[interfaces.length]; for (int i = 0; i < interfaces.length; i++) { this.interfaces[i] = ClassUtils.convertResourcePathToClassName(interfaces[i]); } }
  

 

  
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AnnotationMetadataReadingVisitor 类

public class AnnotationMetadataReadingVisitor extends  ClassMetadataReadingVisitor implements AnnotationMetadata { private final Set<String> annotationSet = new LinkedHashSet<String>(4); private final Map<String, AnnotationAttributes> attributeMap = new LinkedHashMap<String, AnnotationAttributes>(4); public AnnotationMetadataReadingVisitor() { } @Override public AnnotationVisitor visitAnnotation(final String desc, boolean visible) { String className = Type.getType(desc).getClassName(); this.annotationSet.add(className); return new AnnotationAttributesReadingVisitor(className, this.attributeMap); } @Override public Set<String> getAnnotationTypes() { return this.annotationSet; } @Override public boolean hasAnnotation(String annotationType) { return this.annotationSet.contains(annotationType); } @Override public AnnotationAttributes getAnnotationAttributes(String annotationType) { return this.attributeMap.get(annotationType); } @Override public boolean hasSuperClass() { return false; }
}
  

 

  
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SimpleMetadataReader类

 public SimpleMetadataReader(Resource resource) throws IOException { // 提高一点性能吧 InputStream inputStream = new BufferedInputStream(resource.getInputStream()); ClassReader classReader; try { classReader = new ClassReader(inputStream); } finally { inputStream.close(); } AnnotationMetadataReadingVisitor visitor = new AnnotationMetadataReadingVisitor(); classReader.accept(visitor, ClassReader.SKIP_DEBUG); this.annotationMetadata = visitor; this.classMetadata = visitor; this.resource = resource; }
  

 

  
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用ScannedGenericBeanDefinition 专门用来表达通过Scann扫描出的BeanDefiniton。
ClassPathBeanDefinitionScanner类

/**
 * 1. 给定一个package的名称列表，例如
 org.litespring.service.v4,org.litespring.dao.v4"

 2. 对指定的package 进行扫描(scan)，找到那些标记为@Component 的类，创建ScannedGenericBeanDefinition，并且注册到BeanFactory中。

 * Created by xiang.wei on 2018/7/15
 *
 * @author xiang.wei
 */
public class ClassPathBeanDefinitionScanner { private final BeanDefinitionRegistry registry; private PackageResourceLoader resourceLoader = new PackageResourceLoader(); private final Log logger = LogFactory.getLog(getClass()); private BeanNameGenerator beanNameGenerator = new AnnotationBeanNameGenerator(); public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry) { this.registry = registry; } /** * * @param packagesToScan 传入的base-package 字符串 * @return */ public Set<BeanDefinition> doScan(String packagesToScan) { String[] basePackages = StringUtils.tokenizeToStringArray(packagesToScan, ","); Set<BeanDefinition> beanDefinitions = new LinkedHashSet<BeanDefinition>();
// 对每一个basePackages进行循环 for (String basePackage : basePackages) { Set<BeanDefinition> candidates = findCandidateComponents(basePackage); for (BeanDefinition candidate : candidates) { beanDefinitions.add(candidate); registry.registerBeanDefinition(candidate.getID(), candidate); } } return beanDefinitions; } /** * * @param basePackage * @return */ public Set<BeanDefinition> findCandidateComponents(String basePackage) { Set<BeanDefinition> candidates = new LinkedHashSet<BeanDefinition>(); try {
// 先拿到Resource Resource[] resources = this.resourceLoader.getResources(basePackage); for (Resource resource : resources) { try { MetadataReader metadataReader = new SimpleMetadataReader(resource); //  通过metadataReader 获取AnnotationMetadata 看看其是否有Component注解 if (metadataReader.getAnnotationMetadata().hasAnnotation(Component.class.getName())) {
//实例化一个ScannedGenericBeanDefinition ScannedGenericBeanDefinition sbd=new ScannedGenericBeanDefinition(metadataReader.getAnnotationMetadata()); String beanName = this.beanNameGenerator.generateBeanName(sbd, this.registry); sbd.setId(beanName); candidates.add(sbd); } } catch (Throwable ex) { throw new BeanDefinitionStoreException("Failed to read candidate component class:" + resource, ex ); } } } catch (IOException e) { throw new BeanDefinitionStoreException("I/O failure during classpath scanning", e); } return candidates; }
}

  

 

  
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ScannedGenericBeanDefinition类

public class ScannedGenericBeanDefinition extends GenericBeanDefinition implements AnnotatedBeanDefinition { private final AnnotationMetadata metadata; public ScannedGenericBeanDefinition(AnnotationMetadata metadata) { super(); this.metadata = metadata; setBeanClassName(this.metadata.getClassName()); } @Override public AnnotationMetadata getMetadata() { return this.metadata; }

}

  

 

  
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对XmlBeanDefinitionReader类的修改

 private void parseComponentElement(Element element) { String basePackages = element.attributeValue(BASE_PACKAGE_ATTRIBUTE); ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(registry); scanner.doScan(basePackages); }
  

 

  
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源码地址

文章来源: feige.blog.csdn.net，作者：码农飞哥，版权归原作者所有，如需转载，请联系作者。

原文链接：feige.blog.csdn.net/article/details/82315756