如何在 HttpServletRequest 中设置参数？

Question

我正在使用 javax.servlet.http.HttpServletRequest 来实现 Web 应用程序。

使用 getParameter 方法获取请求的参数没有问题。但是我不知道如何在我的请求中设置参数。

Answer 1

你不能，不使用标准 API。 HttpServletRequest 表示服务器收到的请求，因此添加新参数不是有效选项（就 API 而言）。

您原则上可以实现HttpServletRequestWrapper 的子类，它包装原始请求，并拦截getParameter() 方法，并在您转发时传递包装的请求。

如果您走这条路，您应该使用Filter 将您的HttpServletRequest 替换为HttpServletRequestWrapper：

public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
    if (servletRequest instanceof HttpServletRequest) {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        // Check wether the current request needs to be able to support the body to be read multiple times
        if (MULTI_READ_HTTP_METHODS.contains(request.getMethod())) {
            // Override current HttpServletRequest with custom implementation
            filterChain.doFilter(new HttpServletRequestWrapper(request), servletResponse);
            return;
        }
    }
    filterChain.doFilter(servletRequest, servletResponse);
}

Answer 2

如果您真的想这样做，请创建一个 HttpServletRequestWrapper。

public class AddableHttpRequest extends HttpServletRequestWrapper {

   private HashMap params = new HashMap();

   public AddableingHttpRequest(HttpServletRequest request) {
           super(request);
   }

   public String getParameter(String name) {
           // if we added one, return that one
           if ( params.get( name ) != null ) {
                 return params.get( name );
           }
           // otherwise return what's in the original request
           HttpServletRequest req = (HttpServletRequest) super.getRequest();
           return validate( name, req.getParameter( name ) );
   }

   public void addParameter( String name, String value ) {
           params.put( name, value );
   }

}

Answer 3

根据您的问题，我认为您要做的是使用 RequestDispatcher() 存储一些东西（一个对象、一个字符串......），然后将其转发到另一个 servlet。 为此，您不需要设置参数，而是使用属性来设置

void setAttribute(String name, Object o);

然后

Object getAttribute(String name);

Answer 4

最受好评的解决方案通常有效，但对于 Spring 和/或 Spring Boot，除非您专门实现了 getParameterValues()，否则这些值不会连接到带有 @RequestParam 注释的控制器方法中的参数。我在这里和this blog 合并了解决方案：

import java.util.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public class MutableHttpRequest extends HttpServletRequestWrapper {

    private final Map<String, String[]> mutableParams = new HashMap<>();

    public MutableHttpRequest(final HttpServletRequest request) {
        super(request);
    }

    public MutableHttpRequest addParameter(String name, String value) {
        if (value != null)
            mutableParams.put(name, new String[] { value });

        return this;
    }

    @Override
    public String getParameter(final String name) {
        String[] values = getParameterMap().get(name);

        return Arrays.stream(values)
                .findFirst()
                .orElse(super.getParameter(name));
    }

    @Override
    public Map<String, String[]> getParameterMap() {
        Map<String, String[]> allParameters = new HashMap<>();
        allParameters.putAll(super.getParameterMap());
        allParameters.putAll(mutableParams);

        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);
    }
}

请注意，此代码不是超级优化的，但它可以工作。

Answer 5

正如之前的帖子中提到的，使用 HttpServletReqestWrapper 是可行的方法，但是这些帖子中遗漏的部分是除了重写方法 getParameter() 之外，您还应该重写其他与参数相关的方法以产生一致的响应.例如自定义请求包装器添加的参数值也应包含在方法 getParameterMap() 返回的参数映射中。这是一个例子：

   public class AddableHttpRequest extends HttpServletRequestWrapper {

    /** A map containing additional request params this wrapper adds to the wrapped request */
    private final Map<String, String> params = new HashMap<>();

    /**
     * Constructs a request object wrapping the given request.
     * @throws java.lang.IllegalArgumentException if the request is null
     */
    AddableHttpRequest(final HttpServletRequest request) {
        super(request)
    }

    @Override
    public String getParameter(final String name) {
        // if we added one with the given name, return that one
        if ( params.get( name ) != null ) {
            return params.get( name );
        } else {
            // otherwise return what's in the original request
            return super.getParameter(name);
        }
    }


    /**
     * *** OVERRIDE THE METHODS BELOW TO REFLECT PARAMETERS ADDED BY THIS WRAPPER ****
     */

    @Override
    public Map<String, String> getParameterMap() {
        // defaulf impl, should be overridden for an approprivate map of request params
        return super.getParameterMap();
    }

    @Override
    public Enumeration<String> getParameterNames() {
        // defaulf impl, should be overridden for an approprivate map of request params names
        return super.getParameterNames();
    }

    @Override
    public String[] getParameterValues(final String name) {
        // defaulf impl, should be overridden for an approprivate map of request params values
        return super.getParameterValues(name);
    }
}

Answer 6

丢失的 getParameterMap 覆盖最终对我来说是一个真正的问题。所以这就是我最终的结果：

import java.util.HashMap;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

/***
 * Request wrapper enabling the update of a request-parameter.
 * 
 * @author E.K. de Lang
 *
 */
final class HttpServletRequestReplaceParameterWrapper
    extends HttpServletRequestWrapper
{

    private final Map<String, String[]> keyValues;

    @SuppressWarnings("unchecked")
    HttpServletRequestReplaceParameterWrapper(HttpServletRequest request, String key, String value)
    {
        super(request);

        keyValues = new HashMap<String, String[]>();
        keyValues.putAll(request.getParameterMap());
        // Can override the values in the request
        keyValues.put(key, new String[] { value });

    }

    @SuppressWarnings("unchecked")
    HttpServletRequestReplaceParameterWrapper(HttpServletRequest request, Map<String, String> additionalRequestParameters)
    {
        super(request);
        keyValues = new HashMap<String, String[]>();
        keyValues.putAll(request.getParameterMap());
        for (Map.Entry<String, String> entry : additionalRequestParameters.entrySet()) {
            keyValues.put(entry.getKey(), new String[] { entry.getValue() });
        }

    }

    @Override
    public String getParameter(String name)
    {
        if (keyValues.containsKey(name)) {
            String[] strings = keyValues.get(name);
            if (strings == null || strings.length == 0) {
                return null;
            }
            else {
                return strings[0];
            }
        }
        else {
            // Just in case the request has some tricks of it's own.
            return super.getParameter(name);
        }
    }

    @Override
    public String[] getParameterValues(String name)
    {
        String[] value = this.keyValues.get(name);
        if (value == null) {
            // Just in case the request has some tricks of it's own.
            return super.getParameterValues(name);
        }
        else {
            return value;
        }
    }

    @Override
    public Map<String, String[]> getParameterMap()
    {
        return this.keyValues;
    }

}

Answer 7

对不起，为什么不使用以下结构：

request.getParameterMap().put(parameterName, new String[] {parameterValue});