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https://issues.apache.org/jira/browse/SOLR-5951?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13958324#comment-13958324
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ASF subversion and git services commented on SOLR-5951:
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Commit 1584213 from [~thetaphi] in branch 'dev/trunk'
[ https://svn.apache.org/r1584213 ]
SOLR-5951: Fixed SolrDispatchFilter to throw useful exception on startup if
SLF4j logging jars are missing
> SolrDispatchFilter no longer displays useful error message on statup when
> logging jars are missing
> --------------------------------------------------------------------------------------------------
>
> Key: SOLR-5951
> URL: https://issues.apache.org/jira/browse/SOLR-5951
> Project: Solr
> Issue Type: Bug
> Affects Versions: 4.7, 4.7.1
> Reporter: Uwe Schindler
> Assignee: Uwe Schindler
> Fix For: 4.8, 5.0, 4.7.2
>
> Attachments: SOLR-5951.patch
>
>
> We no longer have logging jars in the webapp since SOLR-3706. Because of this
> we added a extra check in SolrDispatchFilter's ctor to print a nice exception
> if the logging jars were failing. This check was unfortunately never tests
> and recently broke:
> The check delays initialization of the Logger instance to inside a try-catch
> block inside the explicit ctor. If it fails with ClassNotFound, it throws
> Exception.
> Recently we upgraded to a newer HttpClient version. Unfortunately
> SolrDispatchFliter also has an implicit constructor a few lines before the
> main constructor:
> {code:java}
> protected final HttpClient httpClient = HttpClientUtil.createClient(new
> ModifiableSolrParams()); // <-- this breaks the detection
>
> private static final Charset UTF8 = StandardCharsets.UTF_8;
> public SolrDispatchFilter() {
> try {
> log = LoggerFactory.getLogger(SolrDispatchFilter.class);
> } catch (NoClassDefFoundError e) {
> throw new SolrException(
> ErrorCode.SERVER_ERROR,
> "Could not find necessary SLF4j logging jars. If using Jetty, the
> SLF4j logging jars need to go in "
> +"the jetty lib/ext directory. For other containers, the
> corresponding directory should be used. "
> +"For more information, see:
> http://wiki.apache.org/solr/SolrLogging";,
> e);
> }
> }
> {code}
> The first line above {{HttpClientUtil.createClient(new
> ModifiableSolrParams());}} breaks the whole thing, because it is executed
> before the declared constructor. The user just sees a ClassNotFoundEx at this
> line of code, the nice error message is hidden.
> Because this is so easy to break, we should make the whole thing more safe
> (any maybe test it). 2 options:
> # Into the webapp add a fake Servlet (not bound to anything, just loaded
> first) that does not use any Solr classes at all, nothing only plain java
> # Alternatively add a Superclass between ServletFilter and SolrDispatchFilter
> (pkg-private). When the servlet container loads SolrDispatchFilter, it has in
> any case to first load the superclass. And this superclass does the check and
> throws ServletException or whatever (no Solr Exception) with the message from
> the current code.
> I tend to the second approach, because it does not need to modify web-inf. It
> will also work with other Solr servlets, they must just extend this hidden
> class. I will provide a patch for that.
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