开发请求包装

    J2EE 规范提供了请求包装机制来修改供下游应用程序或组件使用的请求。本文并不会讨论请求包装和 Servlet 筛选器；有关这两个构件的详细信息，请参见 Java Servlet 2.3 规范。

    要设计请求包装，首先需要 Servlet 筛选器能够指定请求包装的区域设置。因此，您需要一个构造函数，该构造函数接受传入请求对象和 Servlet 筛选器所确定的区域设置作为参数。

    清单 1. LocaleRequestWrapper

public class LocaleRequestWrapper extends HttpServletRequestWrapper
implements com.ibm.wsspi.webcontainer.servlet.IServletRequest
{
private String locale = null;
private Locale localeObj;
private List locales = new ArrayList(1);
public LocaleRequestWrapper(HttpServletRequest request, Locale locale)
{
super(request);
// validate the locale here…if invalid locale is passed
// throw illegal argument exception 
String langCode = locale.getLanguage();
String countryCode = locale.getCountry();
if (langCode != null && langCode.trim().length() > 0 &&
countryCode != null && countryCode.trim().length() > 0) {
this.locale = langCode + "-" + countryCode;
localeObj = new Locale(langCode, countryCode);
}
else if (langCode != null && langCode.trim().length() > 0) {
this.locale = langCode;
localeObj = new Locale(langCode);
}
if (locale != null)
{
locales.add(locale);
}
}
public Object clone() throws CloneNotSupportedException
{
LocaleRequestWrapper crequest = (LocaleRequestWrapper)super.clone();
javax.servlet.ServletRequest inner = crequest.getRequest();
if (inner instanceof IServletRequest)
{
crequest.setRequest(
(HttpServletRequest)((IServletRequest)inner).clone());
} else
{
throw new CloneNotSupportedException();
}
return crequest;
}
} 

    接下来，请求包装需要重写 getHeader 和 getHeaders 方法，以便能在指定的键为 Accept-Languag 时返回 Servlet 筛选器指定的区域设置。

    清单 2. LocaleRequestWrapper getHeader() 和 getHeaders() 方法

public String getHeader(String key)
{
// get the original request 
HttpServletRequest request = (HttpServletRequest)getRequest();
// if the header request is for locale, return the stored locale 
if ("Accept-Language".equalsIgnoreCase(key))
{
if (locale != null) return locale;
// if no locale is set, then return a value that would cause
// WPS to use default language. 
else return request.getHeader(key);
}
// if the requested header is not the locale, return the value
// from the wrapped request 
else
return request.getHeader(key);
}
public Enumeration getHeaders(String key)
{
// get the original request 
HttpServletRequest request = (HttpServletRequest)getRequest();
// if the header request is for locale, return the stored locale 
if ("Accept-Language".equalsIgnoreCase(key))
{
if (locale != null) return Collections.enumeration(locales);
// if no locale is set, then return a value that would cause
// WPS to use default language. 
else return request.getHeaders(key);
}
// if the requested header is not the locale, return the value
// from the wrapped request 
else
return request.getHeaders(key);
} 

    您还需要重写 getLocale 和 getLocales 方法，以返回与 getHeader 方法所返回的相同的区域设置。

    清单 3. LocaleRequestWrapper getLocale() 和 getLocales() 方法

public Locale getLocale()
{
if (localeObj != null) return localeObj;
else
{
// get the original request 
HttpServletRequest request = (HttpServletRequest)getRequest();
return request.getLocale();
}
}
public Enumeration getLocales()
{
if (locale != null) return Collections.enumeration(locales);
else
{
// get the original request 
HttpServletRequest request = (HttpServletRequest)getRequest();
return request.getLocales();
}
}