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The HttpServletResponse Interface

To create cookies, you need to use the addCookie method of javax.servlet.http.HttpServletResponse interface. What's a Java interface? You can think of an interface as a class that defines method names, but not their code. You can't create objects directly using an interface. Instead, you must base a class on that interface—the interface only defines what data members and methods that class will have. As we'll see in Day 11, "Creating More Powerful JavaBeans," using interfaces is as close as you can come in Java to basing a class on more than one other class (in object-oriented programming terms, interfaces represent Java's support for multiple inheritance, as we'll see in Day 13, "Creating More Powerful Servlets").

So where does that leave you? Fortunately, the server has done all the work you'll need here—one of the built-in objects available to you in your JSP code is the response object (see "The JSP Programming Environment" in Day 2, "Handling Data and Operators"), and this is a pre-built object based on the javax.servlet.http.HttpServletResponse interface.

Just as you use the request object to see what data the user has sent to you, you can use the response object to send data back to the user. In this case, you'll use this object to send cookies back to the browser, which will store them. You can see the fields of the javax.servlet.http.HttpServletResponse interface in Table 7.2, and the methods of this interface in Table 7.3. Because the response object is built on this interface, it shares all the methods of the interface, and you'll see how to put them to work in the next topic, creating your own cookies with the addCookie method. You use the various field values in Table 7.2 if you want to send a status report back to the browser, as with the sendError or setStatus methods (which we won't do here).


The convention for fields is that if its name is in capital letters, it's a read-only constant whose value doesn't change.

Table 7.2 HttpServletResponse Fields


Does This


Indicates that a request was accepted for processing, but was not completed.


Indicates that the HTTP server received an invalid response from a server it consulted when acting as a proxy or gateway.


Indicates the request sent by the client was incorrect.


Indicates that the request cannot be completed because of a conflict with the current state of the resource.


Indicates the client can continue.


Indicates the request succeeded and created a new resource on the server.


Indicates that the server cannot meet the request in the Expect request header.


Indicates the server cannot complete the request.


Indicates that the server did not receive a response from a gateway or proxy server in time.


Indicates that the resource is no longer available.


Indicates that the server does not support the HTTP protocol version used in the request.


Indicates an error inside the HTTP server.


Indicates that the request cannot be handled without a specified content length.


Indicates that the method specified in the Request-Line is not allowed.


Indicates that the resource has moved to a new location.


Indicates that the resource has temporarily moved to another location.


Indicates that the resource corresponds to any one of a set.


Indicates that the request was successful but there was no new content to return.


Indicates that the meta information sent by the browser did not come from the server.


Indicates that the resource identified by the request was not acceptable.


Indicates that the requested resource was not available.


Indicates the HTTP server does not support the request.


Indicates that a GET operation found that the resource was available and not modified.

int SC_OK

Indicates the request succeeded.


Indicates that the server has fulfilled the partial GET request.


Reserved for future use.


Indicates that the precondition given in a request header field failed.


Indicates that the client must authenticate itself with the proxy.


Indicates that the request entity is larger than the server can process.


Indicates that the request timed out.


Indicates that the Request-URI field is too long.


Indicates that the server cannot serve the requested data range.


Indicates that the agent will reset the display of the document.


Indicates that the response to the request can be found under a different URI.


Indicates that the HTTP server is overloaded.


Indicates the server is switching protocols.


Indicates that the requested resource is temporarily at a different URI.


Indicates that the request needs HTTP authentication.


Indicates that the request is in a format not supported by the requested resource.


Indicates that the requested resource must be accessed through the proxy.

Table 7.3 HttpServletResponse Methods


Does This

void addCookie(Cookie cookie)

Adds the given cookie to the response.

void addDateHeader(java.lang.String name, long date)

Adds a response header with the given name and date.

void addHeader(java.lang.String name, java.lang.String value)

Adds a response header with the given name and value.

void addIntHeader(java.lang.String name, int value)

Adds a response header with the given name and integer value.

boolean containsHeader (java.lang.String name)

Returns a Boolean value indicating if a response header has been set.

java.lang.String encodeRedirectUrl (java.lang.String url)

Deprecated. As of servlet specification version 2.1, use encodeRedirectURL (String url) instead.

java.lang.String encodeRedirectURL (java.lang.String url)

Encodes the specified URL for use in the sendRedirect method.

java.lang.String encodeUrl (java.lang.String url)

Deprecated. As of servlet specification version 2.1, use encodeURL(String url) instead.

java.lang.String encodeURL (java.lang.String url)

Encodes the specified URL by including the session ID in it.

void sendError(int sc)

Sends an error response to the client using the given status field value.

void sendError(int sc, java.lang.String msg)

Sends an error response to the client using the given field value and text.

void sendRedirect (java.lang.String location)

Sends a temporary redirect response to the browser using the given URL.

void setDateHeader(java.lang.String name, long date)

Sets a response header with the given name and date.

void setHeader(java.lang.String name, java.lang.String value)

Sets a response header with the given name and value.

void setIntHeader(java.lang.String name, int value)

Sets a response header with the given name and integer value.

void setStatus(int sc)

Sets the status code for this response.

void setStatus (int sc, java.lang.String sm)

Deprecated. As of servlet specification version 2.1, use setStatus(int) to send an error with a description.

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