{"id":18,"date":"2003-11-04T22:15:02","date_gmt":"2003-11-05T04:15:02","guid":{"rendered":"http:\/\/www.mooreds.com\/wordpress\/?p=18"},"modified":"2003-11-04T22:15:02","modified_gmt":"2003-11-05T04:15:02","slug":"sending-binary-data-via-struts","status":"publish","type":"post","link":"https:\/\/www.mooreds.com\/wordpress\/archives\/18","title":{"rendered":"Sending Binary Data Via Struts"},"content":{"rendered":"

Struts<\/a> is a MVC web framework. It allows you to specify the paths through a web application in an XML configuration file, and provides some nice tag libraries for JSP manipulation. The views for the states are usually JSPs, and the controller is a servlet provided for you.<\/p>\n

\nThis standard setup is fine, most of the time. But I’ve run into situations, as have others (1<\/a>,2<\/a>), where you need Struts to output a binary file. In my case, I’m sending a dynamic image to a non browser client, and I basically need to write a ByteArrayOutputStream<\/a> to the response output stream.<\/p>\n

\nNow, you’d think I’d be able to do this with a JSP. After all, a JSP is just a servlet turned inside out, right? Well, according to the specification, you’d be right. From page 42 of JSP 1.2 spec:<\/p>\n

\n—————-
\nThe JSP container should not invoke response.getWriter() until the time when the first portion of the content is to be sent to the client. This enables a number of uses of JSP, including using JSP as a language to glue actions that deliver binary content, or reliably forwarding to a servlet, or change dynamically the content type of the response before generating content. See Chapter JSP.3.
\n—————-<\/p>\n

\nBut, according to Tomcat 4.1.24 on the Linux platform, you’d be wrong. When calling ‘java.io.OutputStream rs = response.getOutputStream();’ in my JSP, I get this code generated:<\/p>\n

\n—————<\/p>\n

\n....snip...\n      application = pageContext.getServletContext();\n      config = pageContext.getServletConfig();\n      session = pageContext.getSession();\n      out = pageContext.getOut();\n      _jspx_out = out;\njava.io.OutputStream rs = response.getOutputStream();\n....snip...<\/pre>\n
\n—————<\/p>\n
\nThe JSP is taking my stream before my code has a chance.  Therefore, I get an “getOutputStream() has already been called for this response” error. The weird bit is that this doesn’t seem to happen on Tomcat 4.1.24 on Windows (same version of struts).<\/p>\n
\nSo, what do you do?  You write a servlet instead.  That way you have utter control over the output stream:<\/p>\n
\n—————
\n<\/p>\n
\nimport javax.servlet.http.*;\nimport javax.servlet.*;\nimport java.io.*;\n\npublic class BinaryStreamServlet extends HttpServlet {\n\n   public void service(HttpServletRequest req, HttpServletResponse res)\nthrows ServletException, IOException {\n      String contentType =\n(String)req.getAttribute(\"contentType\");\n      if (contentType == null || \"\".equals(contentType)) {\n         contentType = \"image\/png\"; \/\/ default\n      }\n      res.reset();\n      res.setContentType(contentType);\n      OutputStream sos = res.getOutputStream();\n      ByteArrayOutputStream baos = (ByteArrayOutputStream)req.getAttribute(\"baos\");\n      baos.writeTo(sos);\n   }\n}<\/pre>\n
\n—————<\/p>\n
\nI set up my action classes to cache the ByteArrayOutputStream in the request, with the name “baos.”  I added these lines to my web.xml:<\/p>\n
\n—————<\/p>\n
<servlet>\n      <servlet-name>binaryFileServlet<\/servlet-name>\n       <servlet-class>BinaryStreamServlet<\/servlet-class>\n  <\/servlet>\n....snip...\n  <servlet-mapping>\n    <servlet-name>binaryFileServlet<\/servlet-name>\n    <url-pattern>\/binaryFile<\/url-pattern>\n  <\/servlet-mapping><\/pre>\n
\n—————<\/p>\n
\nand this to my struts-config.xml for any actions that needed to be able to send binary data:<\/p>\n
\n—————<\/p>\n
\n<forward name=\"success\"         path=\"\/binaryFile\"\/><\/pre>\n
\n—————<\/p>\n
\nWorks like a charm.  Leave the JSPs to the character data, and use this simple servlet for binary delivery.<\/p>\n","protected":false},"excerpt":{"rendered":"
Struts is a MVC web framework. It allows you to specify the paths through a web application in an XML configuration file, and provides some nice tag libraries for JSP […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-18","post","type-post","status-publish","format-standard","hentry","category-java"],"_links":{"self":[{"href":"https:\/\/www.mooreds.com\/wordpress\/wp-json\/wp\/v2\/posts\/18","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.mooreds.com\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.mooreds.com\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.mooreds.com\/wordpress\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.mooreds.com\/wordpress\/wp-json\/wp\/v2\/comments?post=18"}],"version-history":[{"count":0,"href":"https:\/\/www.mooreds.com\/wordpress\/wp-json\/wp\/v2\/posts\/18\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.mooreds.com\/wordpress\/wp-json\/wp\/v2\/media?parent=18"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.mooreds.com\/wordpress\/wp-json\/wp\/v2\/categories?post=18"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.mooreds.com\/wordpress\/wp-json\/wp\/v2\/tags?post=18"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}