上文solr源码分析之数据导入DataImporter追溯中提到了solr的工作流程，其核心是各种handler。

handler定义了各种search Component，

  @Override
  public void handleRequestBody(SolrQueryRequest req, SolrQueryResponse rsp) throws Exception
  {
    List<SearchComponent> components  = getComponents();
    ResponseBuilder rb = new ResponseBuilder(req, rsp, components);
}

然后调用组件的prepare方法：

if (timer == null) {
      // non-debugging prepare phase
      for( SearchComponent c : components ) {
        c.prepare(rb);
      }
    } else {
      // debugging prepare phase
      RTimer subt = timer.sub( "prepare" );
      for( SearchComponent c : components ) {
        rb.setTimer( subt.sub( c.getName() ) );
        c.prepare(rb);
        rb.getTimer().stop();
      }
      subt.stop();
    }

再调用组件的process方法：

if(!rb.isDebug()) {
          // Process
          for( SearchComponent c : components ) {
            c.process(rb);
          }
        }
        else {
          // Process
          RTimer subt = timer.sub( "process" );
          for( SearchComponent c : components ) {
            rb.setTimer( subt.sub( c.getName() ) );
            c.process(rb);
            rb.getTimer().stop();
          }
          subt.stop();

          // add the timing info
          if (rb.isDebugTimings()) {
            rb.addDebugInfo("timing", timer.asNamedList() );
          }
        }

从源码上来分析一下search Component，searchComponent的结构如下：

以QueryComponent为例，理解一下它的工作原理。

prepare方法获取查询语句：

 @Override
  public void prepare(ResponseBuilder rb) throws IOException
  {

    SolrQueryRequest req = rb.req;
    SolrParams params = req.getParams();
    if (!params.getBool(COMPONENT_NAME, true)) {
      return;
    }
    SolrQueryResponse rsp = rb.rsp;

    // Set field flags
    ReturnFields returnFields = new SolrReturnFields( req );
    rsp.setReturnFields( returnFields );
    int flags = 0;
    if (returnFields.wantsScore()) {
      flags |= SolrIndexSearcher.GET_SCORES;
    }
    rb.setFieldFlags( flags );

    String defType = params.get(QueryParsing.DEFTYPE, QParserPlugin.DEFAULT_QTYPE);

    // get it from the response builder to give a different component a chance
    // to set it.
    String queryString = rb.getQueryString();
    if (queryString == null) {
      // this is the normal way it‘s set.
      queryString = params.get( CommonParams.Q );
      rb.setQueryString(queryString);
    }

    try {
      QParser parser = QParser.getParser(rb.getQueryString(), defType, req);
      Query q = parser.getQuery();
      if (q == null) {
        // normalize a null query to a query that matches nothing
        q = new MatchNoDocsQuery();
      }

      rb.setQuery( q );

      String rankQueryString = rb.req.getParams().get(CommonParams.RQ);
      if(rankQueryString != null) {
        QParser rqparser = QParser.getParser(rankQueryString, defType, req);
        Query rq = rqparser.getQuery();
        if(rq instanceof RankQuery) {
          RankQuery rankQuery = (RankQuery)rq;
          rb.setRankQuery(rankQuery);
          MergeStrategy mergeStrategy = rankQuery.getMergeStrategy();
          if(mergeStrategy != null) {
            rb.addMergeStrategy(mergeStrategy);
            if(mergeStrategy.handlesMergeFields()) {
              rb.mergeFieldHandler = mergeStrategy;
            }
          }
        } else {
          throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,"rq parameter must be a RankQuery");
        }
      }

      rb.setSortSpec( parser.getSort(true) );
      rb.setQparser(parser);

      final String cursorStr = rb.req.getParams().get(CursorMarkParams.CURSOR_MARK_PARAM);
      if (null != cursorStr) {
        final CursorMark cursorMark = new CursorMark(rb.req.getSchema(),
                                                     rb.getSortSpec());
        cursorMark.parseSerializedTotem(cursorStr);
        rb.setCursorMark(cursorMark);
      }

      String[] fqs = req.getParams().getParams(CommonParams.FQ);
      if (fqs!=null && fqs.length!=0) {
        List<Query> filters = rb.getFilters();
        // if filters already exists, make a copy instead of modifying the original
        filters = filters == null ? new ArrayList<Query>(fqs.length) : new ArrayList<>(filters);
        for (String fq : fqs) {
          if (fq != null && fq.trim().length()!=0) {
            QParser fqp = QParser.getParser(fq, null, req);
            filters.add(fqp.getQuery());
          }
        }
        // only set the filters if they are not empty otherwise
        // fq=&someotherParam= will trigger all docs filter for every request
        // if filter cache is disabled
        if (!filters.isEmpty()) {
          rb.setFilters( filters );
        }
      }
    } catch (SyntaxError e) {
      throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, e);
    }

    if (params.getBool(GroupParams.GROUP, false)) {
      prepareGrouping(rb);
    } else {
      //Validate only in case of non-grouping search.
      if(rb.getSortSpec().getCount() < 0) {
        throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, "‘rows‘ parameter cannot be negative");
      }
    }

    //Input validation.
    if (rb.getQueryCommand().getOffset() < 0) {
      throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, "‘start‘ parameter cannot be negative");
    }
  }

process方法执行查询：

/**
   * Actually run the query
   */
  @Override
  public void process(ResponseBuilder rb) throws IOException
  {
    LOG.debug("process: {}", rb.req.getParams());

    SolrQueryRequest req = rb.req;
    SolrParams params = req.getParams();
    if (!params.getBool(COMPONENT_NAME, true)) {
      return;
    }
    SolrIndexSearcher searcher = req.getSearcher();

    StatsCache statsCache = req.getCore().getStatsCache();

    int purpose = params.getInt(ShardParams.SHARDS_PURPOSE, ShardRequest.PURPOSE_GET_TOP_IDS);
    if ((purpose & ShardRequest.PURPOSE_GET_TERM_STATS) != 0) {
      statsCache.returnLocalStats(rb, searcher);
      return;
    }
    // check if we need to update the local copy of global dfs
    if ((purpose & ShardRequest.PURPOSE_SET_TERM_STATS) != 0) {
      // retrieve from request and update local cache
      statsCache.receiveGlobalStats(req);
    }

    SolrQueryResponse rsp = rb.rsp;
    IndexSchema schema = searcher.getSchema();

    // Optional: This could also be implemented by the top-level searcher sending
    // a filter that lists the ids... that would be transparent to
    // the request handler, but would be more expensive (and would preserve score
    // too if desired).
    String ids = params.get(ShardParams.IDS);
    if (ids != null) {
      SchemaField idField = schema.getUniqueKeyField();
      List<String> idArr = StrUtils.splitSmart(ids, ",", true);
      int[] luceneIds = new int[idArr.size()];
      int docs = 0;
      for (int i=0; i<idArr.size(); i++) {
        int id = searcher.getFirstMatch(
                new Term(idField.getName(), idField.getType().toInternal(idArr.get(i))));
        if (id >= 0)
          luceneIds[docs++] = id;
      }

      DocListAndSet res = new DocListAndSet();
      res.docList = new DocSlice(0, docs, luceneIds, null, docs, 0);
      if (rb.isNeedDocSet()) {
        // TODO: create a cache for this!
        List<Query> queries = new ArrayList<>();
        queries.add(rb.getQuery());
        List<Query> filters = rb.getFilters();
        if (filters != null) queries.addAll(filters);
        res.docSet = searcher.getDocSet(queries);
      }
      rb.setResults(res);

      ResultContext ctx = new ResultContext();
      ctx.docs = rb.getResults().docList;
      ctx.query = null; // anything?
      rsp.add("response", ctx);
      return;
    }

    // -1 as flag if not set.
    long timeAllowed = params.getLong(CommonParams.TIME_ALLOWED, -1L);
    if (null != rb.getCursorMark() && 0 < timeAllowed) {
      // fundamentally incompatible
      throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, "Can not search using both " +
                              CursorMarkParams.CURSOR_MARK_PARAM + " and " + CommonParams.TIME_ALLOWED);
    }

    SolrIndexSearcher.QueryCommand cmd = rb.getQueryCommand();
    cmd.setTimeAllowed(timeAllowed);

    req.getContext().put(SolrIndexSearcher.STATS_SOURCE, statsCache.get(req));

    SolrIndexSearcher.QueryResult result = new SolrIndexSearcher.QueryResult();

    //
    // grouping / field collapsing
    //
    GroupingSpecification groupingSpec = rb.getGroupingSpec();
    if (groupingSpec != null) {
      try {
        boolean needScores = (cmd.getFlags() & SolrIndexSearcher.GET_SCORES) != 0;
        if (params.getBool(GroupParams.GROUP_DISTRIBUTED_FIRST, false)) {
          CommandHandler.Builder topsGroupsActionBuilder = new CommandHandler.Builder()
              .setQueryCommand(cmd)
              .setNeedDocSet(false) // Order matters here
              .setIncludeHitCount(true)
              .setSearcher(searcher);

          for (String field : groupingSpec.getFields()) {
            topsGroupsActionBuilder.addCommandField(new SearchGroupsFieldCommand.Builder()
                .setField(schema.getField(field))
                .setGroupSort(groupingSpec.getGroupSort())
                .setTopNGroups(cmd.getOffset() + cmd.getLen())
                .setIncludeGroupCount(groupingSpec.isIncludeGroupCount())
                .build()
            );
          }

          CommandHandler commandHandler = topsGroupsActionBuilder.build();
          commandHandler.execute();
          SearchGroupsResultTransformer serializer = new SearchGroupsResultTransformer(searcher);
          rsp.add("firstPhase", commandHandler.processResult(result, serializer));
          rsp.add("totalHitCount", commandHandler.getTotalHitCount());
          rb.setResult(result);
          return;
        } else if (params.getBool(GroupParams.GROUP_DISTRIBUTED_SECOND, false)) {
          CommandHandler.Builder secondPhaseBuilder = new CommandHandler.Builder()
              .setQueryCommand(cmd)
              .setTruncateGroups(groupingSpec.isTruncateGroups() && groupingSpec.getFields().length > 0)
              .setSearcher(searcher);

          for (String field : groupingSpec.getFields()) {
            SchemaField schemaField = schema.getField(field);
            String[] topGroupsParam = params.getParams(GroupParams.GROUP_DISTRIBUTED_TOPGROUPS_PREFIX + field);
            if (topGroupsParam == null) {
              topGroupsParam = new String[0];
            }

            List<SearchGroup<BytesRef>> topGroups = new ArrayList<>(topGroupsParam.length);
            for (String topGroup : topGroupsParam) {
              SearchGroup<BytesRef> searchGroup = new SearchGroup<>();
              if (!topGroup.equals(TopGroupsShardRequestFactory.GROUP_NULL_VALUE)) {
                searchGroup.groupValue = new BytesRef(schemaField.getType().readableToIndexed(topGroup));
              }
              topGroups.add(searchGroup);
            }

            secondPhaseBuilder.addCommandField(
                new TopGroupsFieldCommand.Builder()
                    .setField(schemaField)
                    .setGroupSort(groupingSpec.getGroupSort())
                    .setSortWithinGroup(groupingSpec.getSortWithinGroup())
                    .setFirstPhaseGroups(topGroups)
                    .setMaxDocPerGroup(groupingSpec.getGroupOffset() + groupingSpec.getGroupLimit())
                    .setNeedScores(needScores)
                    .setNeedMaxScore(needScores)
                    .build()
            );
          }

          for (String query : groupingSpec.getQueries()) {
            secondPhaseBuilder.addCommandField(new QueryCommand.Builder()
                .setDocsToCollect(groupingSpec.getOffset() + groupingSpec.getLimit())
                .setSort(groupingSpec.getGroupSort())
                .setQuery(query, rb.req)
                .setDocSet(searcher)
                .build()
            );
          }

          CommandHandler commandHandler = secondPhaseBuilder.build();
          commandHandler.execute();
          TopGroupsResultTransformer serializer = new TopGroupsResultTransformer(rb);
          rsp.add("secondPhase", commandHandler.processResult(result, serializer));
          rb.setResult(result);
          return;
        }

        int maxDocsPercentageToCache = params.getInt(GroupParams.GROUP_CACHE_PERCENTAGE, 0);
        boolean cacheSecondPassSearch = maxDocsPercentageToCache >= 1 && maxDocsPercentageToCache <= 100;
        Grouping.TotalCount defaultTotalCount = groupingSpec.isIncludeGroupCount() ?
            Grouping.TotalCount.grouped : Grouping.TotalCount.ungrouped;
        int limitDefault = cmd.getLen(); // this is normally from "rows"
        Grouping grouping =
            new Grouping(searcher, result, cmd, cacheSecondPassSearch, maxDocsPercentageToCache, groupingSpec.isMain());
        grouping.setSort(groupingSpec.getGroupSort())
            .setGroupSort(groupingSpec.getSortWithinGroup())
            .setDefaultFormat(groupingSpec.getResponseFormat())
            .setLimitDefault(limitDefault)
            .setDefaultTotalCount(defaultTotalCount)
            .setDocsPerGroupDefault(groupingSpec.getGroupLimit())
            .setGroupOffsetDefault(groupingSpec.getGroupOffset())
            .setGetGroupedDocSet(groupingSpec.isTruncateGroups());

        if (groupingSpec.getFields() != null) {
          for (String field : groupingSpec.getFields()) {
            grouping.addFieldCommand(field, rb.req);
          }
        }

        if (groupingSpec.getFunctions() != null) {
          for (String groupByStr : groupingSpec.getFunctions()) {
            grouping.addFunctionCommand(groupByStr, rb.req);
          }
        }

        if (groupingSpec.getQueries() != null) {
          for (String groupByStr : groupingSpec.getQueries()) {
            grouping.addQueryCommand(groupByStr, rb.req);
          }
        }

        if (rb.doHighlights || rb.isDebug() || params.getBool(MoreLikeThisParams.MLT, false)) {
          // we need a single list of the returned docs
          cmd.setFlags(SolrIndexSearcher.GET_DOCLIST);
        }

        grouping.execute();
        if (grouping.isSignalCacheWarning()) {
          rsp.add(
              "cacheWarning",
              String.format(Locale.ROOT, "Cache limit of %d percent relative to maxdoc has exceeded. Please increase cache size or disable caching.", maxDocsPercentageToCache)
          );
        }
        rb.setResult(result);

        if (grouping.mainResult != null) {
          ResultContext ctx = new ResultContext();
          ctx.docs = grouping.mainResult;
          ctx.query = null; // TODO? add the query?
          rsp.add("response", ctx);
          rsp.getToLog().add("hits", grouping.mainResult.matches());
        } else if (!grouping.getCommands().isEmpty()) { // Can never be empty since grouping.execute() checks for this.
          rsp.add("grouped", result.groupedResults);
          rsp.getToLog().add("hits", grouping.getCommands().get(0).getMatches());
        }
        return;
      } catch (SyntaxError e) {
        throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, e);
      }
    }

    // normal search result
    searcher.search(result, cmd);
    rb.setResult(result);

    ResultContext ctx = new ResultContext();
    ctx.docs = rb.getResults().docList;
    ctx.query = rb.getQuery();
    rsp.add("response", ctx);
    rsp.getToLog().add("hits", rb.getResults().docList.matches());

    if ( ! rb.req.getParams().getBool(ShardParams.IS_SHARD,false) ) {
      if (null != rb.getNextCursorMark()) {
        rb.rsp.add(CursorMarkParams.CURSOR_MARK_NEXT,
                   rb.getNextCursorMark().getSerializedTotem());
      }
    }

    if(rb.mergeFieldHandler != null) {
      rb.mergeFieldHandler.handleMergeFields(rb, searcher);
    } else {
      doFieldSortValues(rb, searcher);
    }

    doPrefetch(rb);
  }