spring mvc DispatcherServlet详解之拾忆工具类utils

DispatcherServlet的静态初始化

    /**
     * Name of the class path resource (relative to the DispatcherServlet class)
     * that defines DispatcherServlet's default strategy names.
     */
    private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";private static final Properties defaultStrategies;
    static {
        // Load default strategy implementations from properties file.
        // This is currently strictly internal and not meant to be customized
        // by application developers.
        try {
            ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
            defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
        }
        catch (IOException ex) {
            throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + ex.getMessage());
        }
    }

配置文件加载

    /**
     * Load properties from the given resource (in ISO-8859-1 encoding).
     * @param resource the resource to load from
     * @return the populated Properties instance
     * @throws IOException if loading failed
     * @see #fillProperties(java.util.Properties, Resource)
     */
    public static Properties loadProperties(Resource resource) throws IOException {
        Properties props = new Properties();
        fillProperties(props, resource);
        return props;
    }

属性填充：

    /**
     * Fill the given properties from the given resource (in ISO-8859-1 encoding).
     * @param props the Properties instance to fill
     * @param resource the resource to load from
     * @throws IOException if loading failed
     */
    public static void fillProperties(Properties props, Resource resource) throws IOException {
        InputStream is = resource.getInputStream();
        try {
            String filename = resource.getFilename();
            if (filename != null && filename.endsWith(XML_FILE_EXTENSION)) {
                props.loadFromXML(is);
            }
            else {
                props.load(is);
            }
        }
        finally {
            is.close();
        }
    }

我们从这个可以得到什么呢？

我们可以直接拿过来作为读取属性文件的工具类。

DispatcherServlet的策略初始化

初始化策略代码：

    /**
     * Initialize the strategy objects that this servlet uses.
     * <p>May be overridden in subclasses in order to initialize further strategy objects.
     */
    protected void initStrategies(ApplicationContext context) {
        initMultipartResolver(context);
        initLocaleResolver(context);
        initThemeResolver(context);
        initHandlerMappings(context);
        initHandlerAdapters(context);
        initHandlerExceptionResolvers(context);
        initRequestToViewNameTranslator(context);
        initViewResolvers(context);
        initFlashMapManager(context);
    }

我们再看一个这个方法结构图：

从上面的图中我们可以看出它们都共同使用一个方法：

/**
     * Create a List of default strategy objects for the given strategy interface.
     * <p>The default implementation uses the "DispatcherServlet.properties" file (in the same
     * package as the DispatcherServlet class) to determine the class names. It instantiates
     * the strategy objects through the context's BeanFactory.
     * @param context the current WebApplicationContext
     * @param strategyInterface the strategy interface
     * @return the List of corresponding strategy objects
     */
    @SuppressWarnings("unchecked")
    protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
        String key = strategyInterface.getName();
        String value = defaultStrategies.getProperty(key);
        if (value != null) {
            String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
            List<T> strategies = new ArrayList<T>(classNames.length);
            for (String className : classNames) {
                try {
                    Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
                    Object strategy = createDefaultStrategy(context, clazz);
                    strategies.add((T) strategy);
                }
                catch (ClassNotFoundException ex) {
                    throw new BeanInitializationException(
                            "Could not find DispatcherServlet's default strategy class [" + className +
                                    "] for interface [" + key + "]", ex);
                }
                catch (LinkageError err) {
                    throw new BeanInitializationException(
                            "Error loading DispatcherServlet's default strategy class [" + className +
                                    "] for interface [" + key + "]: problem with class file or dependent class", err);
                }
            }
            return strategies;
        }
        else {
            return new LinkedList<T>();
        }
    }

StringUtils 和ClassUtils 可以一个丰富的代码库哦。

更进一步 我们可以从spring的源码库查找所有的*utils.java类，发现一个巨大的代码库，从中学习和重新利用这类工具类库，我们可以完善自己的代码库，加快开发效率。