spring容器启动的加载过程(三)-白红宇

spring容器启动的加载过程(三)

阅读量：5171 次

发布时间：2019-06-13

本文共 20840 字，大约阅读时间需要 69 分钟。

第十步：

public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {    /**     * Load bean definitions from the specified XML file.     * @param resource the resource descriptor for the XML file     * @return the number of bean definitions found     * @throws BeanDefinitionStoreException in case of loading or parsing errors     */     //这里是调用的入口    public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {        return loadBeanDefinitions(new EncodedResource(resource));    }    /**     * Load bean definitions from the specified XML file.     * @param encodedResource the resource descriptor for the XML file,     * allowing to specify an encoding to use for parsing the file     * @return the number of bean definitions found     * @throws BeanDefinitionStoreException in case of loading or parsing errors     */     //这里是载入XML形式的BeanDefinition的地方    public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {        Assert.notNull(encodedResource, "EncodedResource must not be null");        if (logger.isInfoEnabled()) {            logger.info("Loading XML bean definitions from " + encodedResource.getResource());        }        Set
     
       currentResources = this.resourcesCurrentlyBeingLoaded.get();        if (currentResources == null) {            currentResources = new HashSet
      
       (4);            this.resourcesCurrentlyBeingLoaded.set(currentResources);        }        if (!currentResources.add(encodedResource)) {            throw new BeanDefinitionStoreException(                    "Detected cyclic loading of " + encodedResource + " - check your import definitions!");        }        try {            //这里得到XML文件，并得到IO的InputStream准备进行读取            InputStream inputStream = encodedResource.getResource().getInputStream();            try {                InputSource inputSource = new InputSource(inputStream);                if (encodedResource.getEncoding() != null) {                    inputSource.setEncoding(encodedResource.getEncoding());                }                return doLoadBeanDefinitions(inputSource, encodedResource.getResource());            }            finally {                inputStream.close();            }        }        catch (IOException ex) {            throw new BeanDefinitionStoreException(                    "IOException parsing XML document from " + encodedResource.getResource(), ex);        }        finally {            currentResources.remove(encodedResource);            if (currentResources.isEmpty()) {                this.resourcesCurrentlyBeingLoaded.remove();            }        }    }            ...}

第十一步：

/**     * Actually load bean definitions from the specified XML file.     * @param inputSource the SAX InputSource to read from     * @param resource the resource descriptor for the XML file     * @return the number of bean definitions found     * @throws BeanDefinitionStoreException in case of loading or parsing errors     */     //具体的读取过程。这是从特定的XML文件中实际载入的BeanDefinition的地方    protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)            throws BeanDefinitionStoreException {        try {            int validationMode = getValidationModeForResource(resource);            //取得XML文件的Document对象，这个解析过程由DocumentLoader完成，这个DocumentLoader是DefaultDocumentLoader,在定义DocumentLoader的地方创建            Document doc = this.documentLoader.loadDocument(                    inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());            //启动对BeanDefinition解析的详细过程，这个解析会使用到Spring的Bean配置规则。            return registerBeanDefinitions(doc, resource);        }        catch (BeanDefinitionStoreException ex) {            throw ex;        }        catch (SAXParseException ex) {            throw new XmlBeanDefinitionStoreException(resource.getDescription(),                    "Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);        }        catch (SAXException ex) {            throw new XmlBeanDefinitionStoreException(resource.getDescription(),                    "XML document from " + resource + " is invalid", ex);        }        catch (ParserConfigurationException ex) {            throw new BeanDefinitionStoreException(resource.getDescription(),                    "Parser configuration exception parsing XML from " + resource, ex);        }        catch (IOException ex) {            throw new BeanDefinitionStoreException(resource.getDescription(),                    "IOException parsing XML document from " + resource, ex);        }        catch (Throwable ex) {            throw new BeanDefinitionStoreException(resource.getDescription(),                    "Unexpected exception parsing XML document from " + resource, ex);        }    }

第十二步：

public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {    public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {        //这里得到BeanDefinitionDocumentReader来对XML的BeanDefinition进行解析        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();        documentReader.setEnvironment(this.getEnvironment());        //根据通用的XML进行解析，并没有根据Spring的Bean规则        int countBefore = getRegistry().getBeanDefinitionCount();        //具体的解析过程在这个registerBeanDefinitions中完成,这里是按照Spring的Bean规则进行解析        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));        //总的Bean减去通用的，剩下就是spring的bean规则的bean个数        return getRegistry().getBeanDefinitionCount() - countBefore;    }            /**     * Create the {
    @link BeanDefinitionDocumentReader} to use for actually     * reading bean definitions from an XML document.     * The default implementation instantiates the specified "documentReaderClass".     * @see #setDocumentReaderClass     */     //创建BeanDefinitionDocumentReader    protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {        return BeanDefinitionDocumentReader.class.cast(BeanUtils.instantiateClass(this.documentReaderClass));    }    }

第十三步：

public class DefaultBeanDefinitionDocumentReader implements BeanDefinitionDocumentReader {    /**     * {
    @inheritDoc}     * This implementation parses bean definitions according to the "spring-beans" XSD     * (or DTD, historically).     * 
Opens a DOM Document; then initializes the default settings     * specified at the {
    @code 
      } level; then parses the contained bean definitions.     */     //根据spring的bean规则解析bean的定义    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {        this.readerContext = readerContext;        logger.debug("Loading bean definitions");        Element root = doc.getDocumentElement();        doRegisterBeanDefinitions(root);    }                protected void doRegisterBeanDefinitions(Element root) {        String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);        if (StringUtils.hasText(profileSpec)) {            Assert.state(this.environment != null, "environment property must not be null");            String[] specifiedProfiles = StringUtils.tokenizeToStringArray(profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);            if (!this.environment.acceptsProfiles(specifiedProfiles)) {                return;            }        }        BeanDefinitionParserDelegate parent = this.delegate;        this.delegate = createHelper(readerContext, root, parent);        preProcessXml(root);        //委派给delegate解析        parseBeanDefinitions(root, this.delegate);        postProcessXml(root);        this.delegate = parent;    }        protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {        if (delegate.isDefaultNamespace(root)) {            NodeList nl = root.getChildNodes();            for (int i = 0; i < nl.getLength(); i++) {                Node node = nl.item(i);                if (node instanceof Element) {                    Element ele = (Element) node;                    if (delegate.isDefaultNamespace(ele)) {                        parseDefaultElement(ele, delegate);                    }                    else {                        delegate.parseCustomElement(ele);                    }                }            }        }        else {            delegate.parseCustomElement(root);        }    }        ...    }

第十四步：

public class BeanDefinitionParserDelegate {    //在这里面定义了大量的bean的属性    public BeanDefinition parseCustomElement(Element ele) {        return parseCustomElement(ele, null);    }    public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {        String namespaceUri = getNamespaceURI(ele);        NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);        if (handler == null) {            error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);            return null;        }        return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));    }                ...}

第十五步：

public abstract class NamespaceHandlerSupport implements NamespaceHandler {    public BeanDefinition parse(Element element, ParserContext parserContext) {        //这里就是解析Bean得到BeanDefinition的地方了        return findParserForElement(element, parserContext).parse(element, parserContext);    }    /**     * Locates the {
    @link BeanDefinitionParser} from the register implementations using     * the local name of the supplied {
    @link Element}.     */    private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {        String localName = parserContext.getDelegate().getLocalName(element);        BeanDefinitionParser parser = this.parsers.get(localName);        if (parser == null) {            parserContext.getReaderContext().fatal(                    "Cannot locate BeanDefinitionParser for element [" + localName + "]", element);        }        return parser;    }            ...}

在上面的BeanDefinitionParser中的parse，有很多种BeanDefinitionParser对其进行解析，BeanDefinitionParser接口就定义了一个BeanDefinition parse(Element element, ParserContext parserContext);专业用来解析bean的，具体的实现交给他的具体。结构如下图：

我们来看下这个ComponentScanBeanDefinitionParser

public class ComponentScanBeanDefinitionParser implements BeanDefinitionParser {    //这两个是我们常用的属性配置 当然还有别的    private static final String ANNOTATION_CONFIG_ATTRIBUTE = "annotation-config";        private static final String BASE_PACKAGE_ATTRIBUTE = "base-package";    ...    //这里就是他解析的地方了    public BeanDefinition parse(Element element, ParserContext parserContext) {        String[] basePackages = StringUtils.tokenizeToStringArray(element.getAttribute(BASE_PACKAGE_ATTRIBUTE),                ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);        // Actually scan for bean definitions and register them.        ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element);        //得到ClassPathBeanDefinitionScanner，通过它去扫描包中的类文件，注意：这里是类文件而不是类，因为现在这些类还没有被加载，只是ClassLoader能找到这些class的路径而已。        Set
     
       beanDefinitions = scanner.doScan(basePackages);        registerComponents(parserContext.getReaderContext(), beanDefinitions, element);        return null;    }            ...                }

第十六步：再来看看ClassPathBeanDefinitionScanner的doScan方法

protected Set
     
       doScan(String... basePackages) {        Assert.notEmpty(basePackages, "At least one base package must be specified");        //用来保存BeanDefinitionHolder，即Bean的属性        Set
      
        beanDefinitions = new LinkedHashSet
       
        ();        for (String basePackage : basePackages) {            //得到扫描出来的类            Set
        
          candidates = findCandidateComponents(basePackage);            //得到扫描出来的类后，把他加进beanDefinitions中            for (BeanDefinition candidate : candidates) {                ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);                candidate.setScope(scopeMetadata.getScopeName());                String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);                if (candidate instanceof AbstractBeanDefinition) {                    postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);                }                if (candidate instanceof AnnotatedBeanDefinition) {                    AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);                }                if (checkCandidate(beanName, candidate)) {                    BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);                    definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);                    beanDefinitions.add(definitionHolder);                    registerBeanDefinition(definitionHolder, this.registry);                }            }        }        return beanDefinitions;}

第十七：ClassPathScanningCandidateComponentProvider的findCandidateComponents方法

public class ClassPathScanningCandidateComponentProvider implements EnvironmentCapable, ResourceLoaderAware {static final String DEFAULT_RESOURCE_PATTERN = "**/*.class";private ResourcePatternResolver resourcePatternResolver = new PathMatchingResourcePatternResolver();public Set
     
       findCandidateComponents(String basePackage) {        //创建一个candidates，用来保存BeanDefinition        Set
      
        candidates = new LinkedHashSet
       
        ();        try {            String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +                    resolveBasePackage(basePackage) + "/" + this.resourcePattern;            Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);            boolean traceEnabled = logger.isTraceEnabled();            boolean debugEnabled = logger.isDebugEnabled();            for (Resource resource : resources) {                if (traceEnabled) {                    logger.trace("Scanning " + resource);                }                if (resource.isReadable()) {                    try {                        MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);                        if (isCandidateComponent(metadataReader)) {                            //封装一个ScannedGenericBeanDefinition，并设置属性，然后添加进candidates中。                            ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);                            sbd.setResource(resource);                            sbd.setSource(resource);                            if (isCandidateComponent(sbd)) {                                if (debugEnabled) {                                    logger.debug("Identified candidate component class: " + resource);                                }                                candidates.add(sbd);                            }                            else {                                if (debugEnabled) {                                    logger.debug("Ignored because not a concrete top-level class: " + resource);                                }                            }                        }                        else {                            if (traceEnabled) {                                logger.trace("Ignored because not matching any filter: " + resource);                            }                        }                    }                    catch (Throwable ex) {                        throw new BeanDefinitionStoreException(                                "Failed to read candidate component class: " + resource, ex);                    }                }                else {                    if (traceEnabled) {                        logger.trace("Ignored because not readable: " + resource);                    }                }            }        }        catch (IOException ex) {            throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);        }        return candidates;    }            }

来看这两句：

String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX + resolveBasePackage(basePackage) + "/" + this.resourcePattern;

假设我们配置的需要扫描的包名为com.cengle.service，那么packageSearchPath的值就是classpath*:com.cengle.service/**/*.class，意思就是com.cengle.service包(包括子包)下所有class文件；如果配置的是*，那么packageSearchPath的值就是classpath*:*/**/*.class。这里的表达式是Spring自己定义的。Spring会根据这种表达式找出相关的class文件。

Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);

这些资源是怎么得到的。看下面：

public Resource[] getResources(String locationPattern) throws IOException {        Assert.notNull(locationPattern, "Location pattern must not be null");        //判断是否以classpath*:开头        if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {            // a class path resource (multiple resources for same name possible)            //判断多个资源是否有相同的名称            if (getPathMatcher().isPattern(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()))) {                // a class path resource pattern                //得到类路径的资源模式                return findPathMatchingResources(locationPattern);            }            else {                // all class path resources with the given name                //得到所有的类路径资源名字                return findAllClassPathResources(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()));            }        }        else {            // Only look for a pattern after a prefix here            // (to not get fooled by a pattern symbol in a strange prefix).            int prefixEnd = locationPattern.indexOf(":") + 1;            if (getPathMatcher().isPattern(locationPattern.substring(prefixEnd))) {                // a file pattern                //得到文件模式                return findPathMatchingResources(locationPattern);            }            else {                // a single resource with the given name                //得到一个给定名称的资源                return new Resource[] {getResourceLoader().getResource(locationPattern)};            }        }    }    /**     * Find all class location resources with the given location via the ClassLoader.     * @param location the absolute path within the classpath     * @return the result as Resource array     * @throws IOException in case of I/O errors     * @see java.lang.ClassLoader#getResources     * @see #convertClassLoaderURL     */    protected Resource[] findAllClassPathResources(String location) throws IOException {        String path = location;        if (path.startsWith("/")) {            path = path.substring(1);        }        //根据路径，将资源存进一个迭代器中        Enumeration
     
       resourceUrls = getClassLoader().getResources(path);        Set
      
        result = new LinkedHashSet
       
        (16);        while (resourceUrls.hasMoreElements()) {            URL url = resourceUrls.nextElement();            //将迭代器的元素存进set集合中            result.add(convertClassLoaderURL(url));        }        //将集合转化为数组        return result.toArray(new Resource[result.size()]);    }            protected Resource[] findPathMatchingResources(String locationPattern) throws IOException {        String rootDirPath = determineRootDir(locationPattern);        String subPattern = locationPattern.substring(rootDirPath.length());        //根据路径，得到一个资源数组        Resource[] rootDirResources = getResources(rootDirPath);        Set
        
          result = new LinkedHashSet
         
          (16);        //循环数组，将数组元素放进一个set集合中。        for (Resource rootDirResource : rootDirResources) {            rootDirResource = resolveRootDirResource(rootDirResource);            if (isJarResource(rootDirResource)) {                result.addAll(doFindPathMatchingJarResources(rootDirResource, subPattern));            }            else if (rootDirResource.getURL().getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {                result.addAll(VfsResourceMatchingDelegate.findMatchingResources(rootDirResource, subPattern, getPathMatcher()));            }            else {                result.addAll(doFindPathMatchingFileResources(rootDirResource, subPattern));            }        }        if (logger.isDebugEnabled()) {            logger.debug("Resolved location pattern [" + locationPattern + "] to resources " + result);        }        //将集合转化为数组        return result.toArray(new Resource[result.size()]);    }

Spring也是用的ClassLoader加载的class文件。一路追踪，原始的ClassLoader是Thread.currentThread().getContextClassLoader();。到此为止，就拿到class文件了。

Spring会将class信息封装成BeanDefinition，然后再放进DefaultListableBeanFactory的beanDefinitionMap中。

转载于:https://www.cnblogs.com/hjy9420/p/4218140.html

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