WebUtils工具类解析

WebUtils根据名称，知道是Spring当中一个工具类，主要用于Web应用程序，供各种框架使用。

其中有些方法还是挺有用的，比如可以获取Session中的会话属性，获取Cookies，设置Session中的会话属性的值等等

翻译了WebUtils类的文档，其中WebUtils中的方法如下：

1.将一个系统性质设置到上下文根路径

	public static void setWebAppRootSystemProperty(ServletContext servletContext) throws IllegalStateException {
		Assert.notNull(servletContext, "ServletContext must not be null");
		String root = servletContext.getRealPath("/");
		if (root == null) {
			throw new IllegalStateException(
				"Cannot set web app root system property when WAR file is not expanded");
		}
		String param = servletContext.getInitParameter(WEB_APP_ROOT_KEY_PARAM);
		String key = (param != null ? param : DEFAULT_WEB_APP_ROOT_KEY);
		String oldValue = System.getProperty(key);
		if (oldValue != null && !StringUtils.pathEquals(oldValue, root)) {
			throw new IllegalStateException(
				"Web app root system property already set to different value: '" +
				key + "' = [" + oldValue + "] instead of [" + root + "] - " +
				"Choose unique values for the 'webAppRootKey' context-param in your web.xml files!");
		}
		System.setProperty(key, root);
		servletContext.log("Set web app root system property: '" + key + "' = [" + root + "]");
	}

2.移除系统性质

	public static void removeWebAppRootSystemProperty(ServletContext servletContext) {
		Assert.notNull(servletContext, "ServletContext must not be null");
		String param = servletContext.getInitParameter(WEB_APP_ROOT_KEY_PARAM);
		String key = (param != null ? param : DEFAULT_WEB_APP_ROOT_KEY);
		System.getProperties().remove(key);
	}

3.判断“HTML escaping”(HTML转义)对应用是否允许，即看web.xml中的defaultHtmlEscape的值是否设置为true

	public static Boolean getDefaultHtmlEscape(ServletContext servletContext) {
		if (servletContext == null) {
			return null;
		}
		String param = servletContext.getInitParameter(HTML_ESCAPE_CONTEXT_PARAM);
		return (StringUtils.hasText(param)? Boolean.valueOf(param) : null);
	}

4.返回由当前servlet容器提供的 当前Web应用程序的临时目录

	public static File getTempDir(ServletContext servletContext) {
		Assert.notNull(servletContext, "ServletContext must not be null");
		return (File) servletContext.getAttribute(TEMP_DIR_CONTEXT_ATTRIBUTE);
	}

5.返回由servlet容器提供的，Web应用程序中给定路径的实际路径

	public static String getRealPath(ServletContext servletContext, String path) throws FileNotFoundException {
		Assert.notNull(servletContext, "ServletContext must not be null");
		// Interpret location as relative to the web application root directory.
		if (!path.startsWith("/")) {
			path = "/" + path;
		}
		String realPath = servletContext.getRealPath(path);
		if (realPath == null) {
			throw new FileNotFoundException(
					"ServletContext resource [" + path + "] cannot be resolved to absolute file path - " +
					"web application archive not expanded?");
		}
		return realPath;
	}

6.通过一个请求确定会话Session的标识(Id)

	public static String getSessionId(HttpServletRequest request) {
		Assert.notNull(request, "Request must not be null");
		HttpSession session = request.getSession(false);
		return (session != null ? session.getId() : null);
	}

7.通过一个请求，通过name获取session中的属性，如果session中没有属性或者没有session会返回一个null

	public static Object getSessionAttribute(HttpServletRequest request, String name) {
		Assert.notNull(request, "Request must not be null");
		HttpSession session = request.getSession(false);
		return (session != null ? session.getAttribute(name) : null);
	}

8.和7中方法相似，只不过不会返回null，会抛出异常

	public static Object getRequiredSessionAttribute(HttpServletRequest request, String name)
		throws IllegalStateException {

		Object attr = getSessionAttribute(request, name);
		if (attr == null) {
			throw new IllegalStateException("No session attribute '" + name + "' found");
		}
		return attr;
	}

9.通过给定的名称和值设置session中的属性，若果session值为空，会移除session的属性

	public static void setSessionAttribute(HttpServletRequest request, String name, Object value) {
		Assert.notNull(request, "Request must not be null");
		if (value != null) {
			request.getSession().setAttribute(name, value);
		}
		else {
			HttpSession session = request.getSession(false);
			if (session != null) {
				session.removeAttribute(name);
			}
		}
	}

10.获取指定的会话属性，如果没有找到的话会创建并设置新的属性。其中给定的类需要有一个公共的无参构造函数。

	public static Object getOrCreateSessionAttribute(HttpSession session, String name, Class<?> clazz)
			throws IllegalArgumentException {

		Assert.notNull(session, "Session must not be null");
		Object sessionObject = session.getAttribute(name);
		if (sessionObject == null) {
			try {
				sessionObject = clazz.newInstance();
			}
			catch (InstantiationException ex) {
				throw new IllegalArgumentException(
					"Could not instantiate class [" + clazz.getName() +
					"] for session attribute '" + name + "': " + ex.getMessage());
			}
			catch (IllegalAccessException ex) {
				throw new IllegalArgumentException(
					"Could not access default constructor of class [" + clazz.getName() +
					"] for session attribute '" + name + "': " + ex.getMessage());
			}
			session.setAttribute(name, sessionObject);
		}
		return sessionObject;
	}

11.返回给定会话的最佳可用互斥量：即为给定会话同步的对象。返回会话互斥属性（如果可用）;通常情况下，这意味着需要定义HttpSessionMutexListener在{code web.xml}中。 回到HttpSession本身如果没有找到互斥属性。会话互斥确保在期间是相同的对象会话的整个生命周期，在定义的密钥下可用由SESSION_MUTEX_ATTRIBUTE常量定义。 它作为一个在当前会话上同步锁定的安全引用。在很多情况下，HttpSession引用本身是一个安全的互斥体同样，因为它始终是相同的对象参考相同的活动逻辑会话。 但是，这并不能保证不同的servlet容器; 唯一的100％安全方式是会话互斥。

	public static Object getSessionMutex(HttpSession session) {
		Assert.notNull(session, "Session must not be null");
		Object mutex = session.getAttribute(SESSION_MUTEX_ATTRIBUTE);
		if (mutex == null) {
			mutex = session;
		}
		return mutex;
	}

12.返回指定类型的合适的请求对象，如果可用，会unwrapping给定的request请求

	public static <T> T getNativeRequest(ServletRequest request, Class<T> requiredType) {
		if (requiredType != null) {
			if (requiredType.isInstance(request)) {
				return (T) request;
			}
			else if (request instanceof ServletRequestWrapper) {
				return getNativeRequest(((ServletRequestWrapper) request).getRequest(), requiredType);
			}
		}
		return null;
	}

13.和12方法类似，应用于response

	public static <T> T getNativeResponse(ServletResponse response, Class<T> requiredType) {
		if (requiredType != null) {
			if (requiredType.isInstance(response)) {
				return (T) response;
			}
			else if (response instanceof ServletResponseWrapper) {
				return getNativeResponse(((ServletResponseWrapper) response).getResponse(), requiredType);
			}
		}
		return null;
	}

14.判断请求是否是一个包含(Include)请求，即不是从外部进入的顶级Http请求。

	public static boolean isIncludeRequest(ServletRequest request) {
		return (request.getAttribute(INCLUDE_REQUEST_URI_ATTRIBUTE) != null);
	}

15.Servlet规范的错误属性，Servlet2.3规范中定义的属性，用于错误页面直接呈现，而不是通过Servlet容器的错误页面解析

	public static void exposeErrorRequestAttributes(HttpServletRequest request, Throwable ex, String servletName) {
		exposeRequestAttributeIfNotPresent(request, ERROR_STATUS_CODE_ATTRIBUTE, HttpServletResponse.SC_OK);
		exposeRequestAttributeIfNotPresent(request, ERROR_EXCEPTION_TYPE_ATTRIBUTE, ex.getClass());
		exposeRequestAttributeIfNotPresent(request, ERROR_MESSAGE_ATTRIBUTE, ex.getMessage());
		exposeRequestAttributeIfNotPresent(request, ERROR_EXCEPTION_ATTRIBUTE, ex);
		exposeRequestAttributeIfNotPresent(request, ERROR_REQUEST_URI_ATTRIBUTE, request.getRequestURI());
		exposeRequestAttributeIfNotPresent(request, ERROR_SERVLET_NAME_ATTRIBUTE, servletName);
	}

16.如果不存在？ 公开指定的请求属性       （有疑问）

	private static void exposeRequestAttributeIfNotPresent(ServletRequest request, String name, Object value) {
		if (request.getAttribute(name) == null) {
			request.setAttribute(name, value);
		}
	}

17.清除类似方法15中定义的错误属性，遵循servlet2.3规范

	public static void clearErrorRequestAttributes(HttpServletRequest request) {
		request.removeAttribute(ERROR_STATUS_CODE_ATTRIBUTE);
		request.removeAttribute(ERROR_EXCEPTION_TYPE_ATTRIBUTE);
		request.removeAttribute(ERROR_MESSAGE_ATTRIBUTE);
		request.removeAttribute(ERROR_EXCEPTION_ATTRIBUTE);
		request.removeAttribute(ERROR_REQUEST_URI_ATTRIBUTE);
		request.removeAttribute(ERROR_SERVLET_NAME_ATTRIBUTE);
	}

18.将给定的Map公开为请求属性，使用键作为属性名称并将值作为相应的属性值。 键需要是字符串

	public static void exposeRequestAttributes(ServletRequest request, Map<String, ?> attributes) {
		Assert.notNull(request, "Request must not be null");
		Assert.notNull(attributes, "Attributes Map must not be null");
		for (Map.Entry<String, ?> entry : attributes.entrySet()) {
			request.setAttribute(entry.getKey(), entry.getValue());
		}
	}

19.检索具有给定名称的第一个cookie。注意多个Cookie可以具有相同的名称，但路径和域不同。

	public static Cookie getCookie(HttpServletRequest request, String name) {
		Assert.notNull(request, "Request must not be null");
		Cookie cookies[] = request.getCookies();
		if (cookies != null) {
			for (Cookie cookie : cookies) {
				if (name.equals(cookie.getName())) {
					return cookie;
				}
			}
		}
		return null;
	}

20.检查请求中是否有通过按钮或者图像的特定的输入类型=“submit”参数

	public static boolean hasSubmitParameter(ServletRequest request, String name) {
		Assert.notNull(request, "Request must not be null");
		if (request.getParameter(name) != null) {
			return true;
		}
		for (String suffix : SUBMIT_IMAGE_SUFFIXES) {
			if (request.getParameter(name + suffix) != null) {
				return true;
			}
		}
		return false;
	}

21.从给定的请求参数中获取一个命名参数。可以参阅方法{findParameterValue}用于查找算法的描述

	public static String findParameterValue(ServletRequest request, String name) {
		return findParameterValue(request.getParameterMap(), name);
	}

22.获取参数值通过以下的算法：（算法补充）

public static String findParameterValue(Map<String, ?> parameters, String name) {
		// First try to get it as a normal name=value parameter
		Object value = parameters.get(name);
		if (value instanceof String[]) {
			String[] values = (String[]) value;
			return (values.length > 0 ? values[0] : null);
		}
		else if (value != null) {
			return value.toString();
		}
		// If no value yet, try to get it as a name_value=xyz parameter
		String prefix = name + "_";
		for (String paramName : parameters.keySet()) {
			if (paramName.startsWith(prefix)) {
				// Support images buttons, which would submit parameters as name_value.x=123
				for (String suffix : SUBMIT_IMAGE_SUFFIXES) {
					if (paramName.endsWith(suffix)) {
						return paramName.substring(prefix.length(), paramName.length() - suffix.length());
					}
				}
				return paramName.substring(prefix.length());
			}
		}
		// We couldn't find the parameter value...
		return null;
	}

23.返回包含具有给定前缀的所有参数的map。将单个值映射为String，多个值映射到String数组。

	public static Map<String, Object> getParametersStartingWith(ServletRequest request, String prefix) {
		Assert.notNull(request, "Request must not be null");
		Enumeration<String> paramNames = request.getParameterNames();
		Map<String, Object> params = new TreeMap<String, Object>();
		if (prefix == null) {
			prefix = "";
		}
		while (paramNames != null && paramNames.hasMoreElements()) {
			String paramName = paramNames.nextElement();
			if ("".equals(prefix) || paramName.startsWith(prefix)) {
				String unprefixed = paramName.substring(prefix.length());
				String[] values = request.getParameterValues(paramName);
				if (values == null || values.length == 0) {
					// Do nothing, no values found at all.
				}
				else if (values.length > 1) {
					params.put(unprefixed, values);
				}
				else {
					params.put(unprefixed, values[0]);
				}
			}
		}
		return params;
	}

24.返回请求中指定的目标页面

	public static int getTargetPage(ServletRequest request, String paramPrefix, int currentPage) {
		Enumeration<String> paramNames = request.getParameterNames();
		while (paramNames.hasMoreElements()) {
			String paramName = paramNames.nextElement();
			if (paramName.startsWith(paramPrefix)) {
				for (int i = 0; i < WebUtils.SUBMIT_IMAGE_SUFFIXES.length; i++) {
					String suffix = WebUtils.SUBMIT_IMAGE_SUFFIXES[i];
					if (paramName.endsWith(suffix)) {
						paramName = paramName.substring(0, paramName.length() - suffix.length());
					}
				}
				return Integer.parseInt(paramName.substring(paramPrefix.length()));
			}
		}
		return currentPage;
	}

25.从给定的请求URL路径中提取URL文件名

	public static String extractFilenameFromUrlPath(String urlPath) {
		String filename = extractFullFilenameFromUrlPath(urlPath);
		int dotIndex = filename.lastIndexOf('.');
		if (dotIndex != -1) {
			filename = filename.substring(0, dotIndex);
		}
		return filename;
	}

26.从给定的请求URL路径中提取完整的URL文件名（包括文件扩展名）。正确地解析嵌套路径，例如“/products/view.html”。

	public static String extractFullFilenameFromUrlPath(String urlPath) {
		int end = urlPath.indexOf(';');
		if (end == -1) {
			end = urlPath.indexOf('?');
			if (end == -1) {
				end = urlPath.length();
			}
		}
		int begin = urlPath.lastIndexOf('/', end) + 1;
		return urlPath.substring(begin, end);
	}

27.用矩阵变量解析给定的字符串。 一个例子字符串会看起来像这样{@code“q1 = a; q1 = b; q2 = a，b，c”}。 结果地图将包含

使用值{@code [“a”，“b”]}的密钥{@code“q1”}和{@code“q2”}和{@code [“a”，“b”，“c”]}。

	public static MultiValueMap<String, String> parseMatrixVariables(String matrixVariables) {
		MultiValueMap<String, String> result = new LinkedMultiValueMap<String, String>();
		if (!StringUtils.hasText(matrixVariables)) {
			return result;
		}
		StringTokenizer pairs = new StringTokenizer(matrixVariables, ";");
		while (pairs.hasMoreTokens()) {
			String pair = pairs.nextToken();
			int index = pair.indexOf('=');
			if (index != -1) {
				String name = pair.substring(0, index);
				String rawValue = pair.substring(index + 1);
				for (String value : StringUtils.commaDelimitedListToStringArray(rawValue)) {
					result.add(name, value);
				}
			}
			else {
				result.add(pair, "");
			}
		}
		return result;
	}