springioc之验证模型获取


top-10-reasons-to-use-spring-framework-1.jpg
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

文章作者: AnonyStar
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