《spring源码解读》 - ioc之验证模型获取

我们上一篇文章最后调用到 `org.springframework.beans.factory.xml. XmlBeanDefinitionReader#doLoadDocument(...)

` 方法，该方法主要代码如下：

protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {
		//getValidationModeForResource是数据验证模型
		return this.documentLoader.loadDocument(inputSource, getEntityResolver(), this.errorHandler,
				getValidationModeForResource(resource), isNamespaceAware());
	}

我们这篇文章主要以 #getValidationModeForResource(...) 方法作为切入，来分析一下验证模型的主要方法，关于spring中的数据验证、绑定等内容我们在后面文章一点点的来挖掘

1.getValidationModeForResource

/**
	 * 禁止只用验证模型
	 * Indicates that the validation should be disabled.
	 */
	public static final int VALIDATION_NONE = XmlValidationModeDetector.VALIDATION_NONE;
	/**
	 * 使用自动检测验证模型
	 * Indicates that the validation mode should be detected automatically.
	 */
	public static final int VALIDATION_AUTO = XmlValidationModeDetector.VALIDATION_AUTO;
	/**
	 * 使用DTD验证模型
	 * Indicates that DTD validation should be used.
	 */
	public static final int VALIDATION_DTD = XmlValidationModeDetector.VALIDATION_DTD;
	/**
	 * 使用XSD验证模型
	 * Indicates that XSD validation should be used.
	 */
	public static final int VALIDATION_XSD = XmlValidationModeDetector.VALIDATION_XSD;
	/**
	 * 确定当前 resource资源需要的验证模型 默认自动模式
	 * 如果显式的配置了验证模型，则用配置的，如果没有则从Resource中来获取
	 * Determine the validation mode for the specified {@link Resource}.
	 * If no explicit validation mode has been configured, then the validation
	 * mode gets {@link #detectValidationMode detected} from the given resource.
	 * <p>Override this method if you would like full control over the validation
	 * mode, even when something other than {@link #VALIDATION_AUTO} was set.
	 * @see #detectValidationMode
	 */
	protected int getValidationModeForResource(Resource resource) {
		// <1> 获取指定的验证模式
		int validationModeToUse = getValidationMode();
		// <2> 如果有指定的模式 则直接返回，
		if (validationModeToUse != VALIDATION_AUTO) {
			return validationModeToUse;
		}
		//<3> 没有指定的 那么通resource中去获取
		int detectedMode = detectValidationMode(resource);
		if (detectedMode != VALIDATION_AUTO) {
			return detectedMode;
		}
		// <4> 若以上都不满足则使用XSD模式
		// Hmm, we didn't get a clear indication... Let's assume XSD,
		// since apparently no DTD declaration has been found up until
		// detection stopped (before finding the document's root tag).
		return VALIDATION_XSD;
	}

对上述代码我们做简单分析

• <1>处调用 #getValidationMode() 方法来获取指定的验证模式 ，这里的 validationMode 如果是外部手动设置的，那么就直接返回，

/**
	 * Set the validation mode to use. Defaults to {@link #VALIDATION_AUTO}.
	 * <p>Note that this only activates or deactivates validation itself.
	 * If you are switching validation off for schema files, you might need to
	 * activate schema namespace support explicitly: see {@link #setNamespaceAware}.
	 */
	public void setValidationMode(int validationMode) {
		this.validationMode = validationMode;
	}
	/**
	 * Return the validation mode to use.
	 */
	public int getValidationMode() {
		return this.validationMode;
	}

• <3>处调用 #detectValidationMode() 方法来自动获取验证模型，代码如下：

/**
	 * 进行自动检测指定的XML用那种检测模型
	 * Detect which kind of validation to perform on the XML file identified
	 * by the supplied {@link Resource}. If the file has a {@code DOCTYPE}
	 * definition then DTD validation is used otherwise XSD validation is assumed.
	 * <p>Override this method if you would like to customize resolution
	 * of the {@link #VALIDATION_AUTO} mode.
	 */
	protected int detectValidationMode(Resource resource) {
		// <1> 资源是否打开
		if (resource.isOpen()) {
			throw new BeanDefinitionStoreException(
					"Passed-in Resource [" + resource + "] contains an open stream: " +
					"cannot determine validation mode automatically. Either pass in a Resource " +
					"that is able to create fresh streams, or explicitly specify the validationMode " +
					"on your XmlBeanDefinitionReader instance.");
		}
		InputStream inputStream;
		try {
			inputStream = resource.getInputStream();
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"Unable to determine validation mode for [" + resource + "]: cannot open InputStream. " +
					"Did you attempt to load directly from a SAX InputSource without specifying the " +
					"validationMode on your XmlBeanDefinitionReader instance?", ex);
		}
		try {
            ////<2> 调用XmlValidationModeDetector 中的真实实现 传入 inputStream
			return this.validationModeDetector.detectValidationMode(inputStream);
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException("Unable to determine validation mode for [" +
					resource + "]: an error occurred whilst reading from the InputStream.", ex);
		}
	}

2.detectValidationMode

上面 <3>处调用了 #detectValidationMode() 方法，这里 validationModeDetector 对象是类中的一个不可变成员变量 定义如下：

private final XmlValidationModeDetector validationModeDetector = new XmlValidationModeDetector();

#detectValidationMode() 方法的具体实现如下：

/**
	 * 通过指定的 inputStream 来检测 XML 中的验证模型
	 * Detect the validation mode for the XML document in the supplied {@link InputStream}.
	 * Note that the supplied {@link InputStream} is closed by this method before returning.
	 * @param inputStream the InputStream to parse
	 * @throws IOException in case of I/O failure
	 * @see #VALIDATION_DTD
	 * @see #VALIDATION_XSD
	 */
	public int detectValidationMode(InputStream inputStream) throws IOException {
		//<1> 通过 BufferedReader 读取inputStream
		// Peek into the file to look for DOCTYPE.
		BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
		try {
			//<2> 是否是DTD验证模式 ，默认否
			boolean isDtdValidated = false;
			String content;
			// <3> 逐行读取内容
			while ((content = reader.readLine()) != null) {
				content = consumeCommentTokens(content);
				// <4> 如果是注释或者为空这跳过
				if (this.inComment || !StringUtils.hasText(content)) {
					continue;
				}
				// <5> 校验是否包含 DOCTYPE 若包含则为DTD模式
				if (hasDoctype(content)) {
					isDtdValidated = true;
					break;
				}
				// <6> 校验是否是打开的标签， 如果一行有 <  并且后面跟着是字母，那么返回
				if (hasOpeningTag(content)) {
					// End of meaningful data...
					break;
				}
			}
			// 确定解析方式
			return (isDtdValidated ? VALIDATION_DTD : VALIDATION_XSD);
		}
		catch (CharConversionException ex) {
			// Choked on some character encoding...
			// Leave the decision up to the caller.
			return VALIDATION_AUTO;
		}
		finally {
			//关闭流
			reader.close();
		}
	}

• 上述代码中<5>处校验是否包含了 DOCTYPE 字符，具体代码如下：

/**
	 * The token in a XML document that declares the DTD to use for validation
	 * and thus that DTD validation is being used.
	 */
	private static final String DOCTYPE = "DOCTYPE";
	/**
	 * 判断是否包含 DOCTYPE
	 * Does the content contain the DTD DOCTYPE declaration?
	 */
	private boolean hasDoctype(String content) {
		return content.contains(DOCTYPE);
	}

• <6>处进行了标签的打开判断，代码如下：

/**
	 * Does the supplied content contain an XML opening tag. If the parse state is currently
	 * in an XML comment then this method always returns false. It is expected that all comment
	 * tokens will have consumed for the supplied content before passing the remainder to this method.
	 */
	private boolean hasOpeningTag(String content) {
		if (this.inComment) {
			return false;
		}
		int openTagIndex = content.indexOf('<'); // 获取字符中 < 的索引
		return (openTagIndex > -1  // 存在 <
				&& (content.length() > openTagIndex + 1) // 并且后面还有内容
				&&Character.isLetter(content.charAt(openTagIndex + 1)));//后面必须是字母
	}

• 如果抛出异常时 CharConversionException 则默认设置为自动 VALIDATION_AUTO

本文由AnonyStar 发布,可转载但需声明原文出处。

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