是否可以添加到请求的可用参数(HttpServletRequest)

子类 HttpServletRequestWrapper 并覆盖 getParameter

我通常将原始HttpServletRequest包装成一个新的CustomHttpServletRequest,作为原始请求的代理,然后将这个新的CustomHttpServletRequest传递给过滤器链。

这是过滤器的一个示例:

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest httpRequest = (HttpServletRequest) request;
    HttpServletRequest customRequest = new CustomHttpServletRequest(httpRequest);
    customRequest.addParameter(xxx, "xxx");
    chain.doFilter(customRequest, response);
}

然后用原始参数+新参数构造另一个请求并再次发送。

HttpServletRequest是不可变的,无法更改它。

您可以将HttpServletRequest包装到新的HttpServletRequestWrapper对象中,并覆盖一些方法。

http://www.ocpsoft.org/opensource/how-to-safely-add-modify-servlet-request-parameter-values/ .

要在筛选器中添加参数,请执行以下操作:

public class MyFilter implements Filter {
...
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    if (request instanceof HttpServletRequest) {
        HttpServletRequest httprequest = (HttpServletRequest) request;
        Map<String, String[]> extraParams = new HashMap<String, String[]>();
        extraParams.put("myparamname", String[] { "myparamvalue" });
        request = new WrappedRequestWithParameter(httprequest, extraParams);
    }
    chain.doFilter(request, response);
}
...

class WrappedRequestWithParameter extends HttpServletRequestWrapper {
    private final Map<String, String[]> modifiableParameters;
    private Map<String, String[]> allParameters = null;

    public WrappedRequestWithParameter(final HttpServletRequest request, final Map<String, String[]> additionalParams) {
        super(request);
        modifiableParameters = new TreeMap<String, String[]>();
        modifiableParameters.putAll(additionalParams);
    }

    @Override
    public String getParameter(final String name) {
        String[] strings = getParameterMap().get(name);
        if (strings != null) {
            return strings[0];
        }
        return super.getParameter(name);
    }

    @Override
    public Map<String, String[]> getParameterMap() {
        if (allParameters == null) {
            allParameters = new TreeMap<String, String[]>();
            allParameters.putAll(super.getParameterMap());
            allParameters.putAll(modifiableParameters);
        }
        // Return an unmodifiable collection because we need to uphold the interface contract.
        return Collections.unmodifiableMap(allParameters);
    }

    @Override
    public Enumeration<String> getParameterNames() {
        return Collections.enumeration(getParameterMap().keySet());
    }

    @Override
    public String[] getParameterValues(final String name) {
        return getParameterMap().get(name);
    }
}
}

为什么不将变量存储为请求范围属性,而不是尝试将它们附加到请求参数中?

否则,可以使用强类型的setAttribute()方法。因此,可以使用getAttribute()方法。。。