Solr4.8.0源码分析(2)之Solr的启动(一)

上文写到Solr的启动过程是在SolrDispatchFilter的init()里实现，当Tomcat启动时候会自动调用init();

Solr的启动主要在 this.cores = createCoreContainer();语句中实现。

/**
  *初始化，当tomcat启动时候开始初始化，其中主要调用createCoreContainer来实现Solr的初始化
  */
public void init(FilterConfig config) throws ServletException
  {
    log.info("SolrDispatchFilter.init()");

    try {
      // web.xml configuration
      this.pathPrefix = config.getInitParameter( "path-prefix" );

      this.cores = createCoreContainer();
      log.info("user.dir=" + System.getProperty("user.dir"));
    }
    catch( Throwable t ) {
      // catch this so our filter still works
      log.error( "Could not start Solr. Check solr/home property and the logs");
      SolrCore.log( t );
      if (t instanceof Error) {
        throw (Error) t;
      }
    }

    log.info("SolrDispatchFilter.init() done");
  }

Solr的启动过程主要包括：

1. 获取SolrHome：分别先后通过JNDI，System property，default directory三种方式尝试获取
2. 实例化启动过程中使用的类加载器SolrResourceLoader
3. 加载solrhome下的solr.xml文件，封装为ConfigSolr
4. 实例化一个CoreContainer,通过CoreContainer来加载cores
5. 遍历SolrHome，当寻找到含有core.properties的文件夹，则作为一个core
6. 多线程加载cores
7. 加载每个core时先加载solrconfig.xml封装为SolrConfig
8. 再加载schema.xml封装为IndexSchema
9. 最后实例化SolrCore

以下是createCoreContainer()实现代码，该函数就包含了以上的启动过程。

  /**
   * Override this to change CoreContainer initialization
   * @return a CoreContainer to hold this server's cores
   */
  protected CoreContainer createCoreContainer() {
    SolrResourceLoader loader = new SolrResourceLoader(SolrResourceLoader.locateSolrHome()); 
    ConfigSolr config = loadConfigSolr(loader);
    CoreContainer cores = new CoreContainer(loader, config);
    cores.load();
    return cores;
  }

 1. 获取SolrHome信息

 Solr通过三种方式来获取SolrHome,分别是JNDI,System property,以及当前路径。

 JNDI的java:comp/env/solr/home的获取，主要通过在tomcat/conf/Catalina/localhost目录下新建solr.xml。Tomcat启动的时候就会该目录下自动获取  SolrHome的信息.

 System property的SolrHome获取是直接在tomcat启动脚本catalina.sh中加入set JAVA_OPTS -Dsolr.solr.home=/Users/rcf/workspace/java/solr 。

 最后的获取SolrHome的方式就是在当前目录下查找。

  /**
   * Determines the solrhome from the environment.
   * Tries JNDI (java:comp/env/solr/home) then system property (solr.solr.home);
   * if both fail, defaults to solr/
   * @return the instance directory name
   */
  /**
   * Finds the solrhome based on looking up the value in one of three places:
   * <ol>
   *  <li>JNDI: via java:comp/env/solr/home</li>
   *  <li>The system property solr.solr.home</li>
   *  <li>Look in the current working directory for a solr/ directory</li> 
   * </ol>
   *
   * The return value is normalized.  Normalization essentially means it ends in a trailing slash.
   * @return A normalized solrhome
   * @see #normalizeDir(String)
   */
  public static String locateSolrHome() {

    String home = null;
    // Try JNDI
    try {
      Context c = new InitialContext();
      home = (String)c.lookup("java:comp/env/"+project+"/home");
      log.info("Using JNDI solr.home: "+home );
    } catch (NoInitialContextException e) {
      log.info("JNDI not configured for "+project+" (NoInitialContextEx)");
    } catch (NamingException e) {
      log.info("No /"+project+"/home in JNDI");
    } catch( RuntimeException ex ) {
      log.warn("Odd RuntimeException while testing for JNDI: " + ex.getMessage());
    } 
    
    // Now try system property
    if( home == null ) {
      String prop = project + ".solr.home";
      home = System.getProperty(prop);
      if( home != null ) {
        log.info("using system property "+prop+": " + home );
      }
    }
    
    // if all else fails, try 
    if( home == null ) {
      home = project + '/';
      log.info(project + " home defaulted to '" + home + "' (could not find system property or JNDI)");
    }
    return normalizeDir( home );
  }

<Context docBase="/Users/rcf/workspace/java/tomcat/apache-tomcat-8.0.9/webapps/solr.war" debug="0" crossContext="true" > 
    <Environment name="solr/home" type="java.lang.String" value="/Users/rcf/workspace/java/solr" override="true" />
</Context>  

获取完SolrHome后,就会实例化SolrResourceLoader。因为传进去的parent是null，所以parents是ContextClassLoader，并且加载了SolrHome/lib/下的文件.

  /**
   * <p>
   * This loader will delegate to the context classloader when possible,
   * otherwise it will attempt to resolve resources using any jar files
   * found in the "lib/" directory in the specified instance directory.
   * </p>
   *
   * @param instanceDir - base directory for this resource loader, if null locateSolrHome() will be used.
   * @see #locateSolrHome
   */
  public SolrResourceLoader( String instanceDir, ClassLoader parent, Properties coreProperties )
  {
    if( instanceDir == null ) {
      this.instanceDir = SolrResourceLoader.locateSolrHome();
      log.info("new SolrResourceLoader for deduced Solr Home: '{}'", 
               this.instanceDir);
    } else{
      this.instanceDir = normalizeDir(instanceDir);
      log.info("new SolrResourceLoader for directory: '{}'",
               this.instanceDir);
    }
    
    this.classLoader = createClassLoader(null, parent);
    addToClassLoader("./lib/", null, true);
    reloadLuceneSPI();
    this.coreProperties = coreProperties;
  }

  /**
   * Convenience method for getting a new ClassLoader using all files found
   * in the specified lib directory.
   */
  static URLClassLoader createClassLoader(final File libDir, ClassLoader parent) {
    if ( null == parent ) {
      parent = Thread.currentThread().getContextClassLoader();
    }
    return replaceClassLoader(URLClassLoader.newInstance(new URL[0], parent),
                              libDir, null);
  }

 1   /**
   * Adds every file/dir found in the baseDir which passes the specified Filter
   * to the ClassLoader used by this ResourceLoader.  This method <b>MUST</b>
   * only be called prior to using this ResourceLoader to get any resources, otherwise
   * it's behavior will be non-deterministic. You also have to {link @reloadLuceneSPI}
   * before using this ResourceLoader.
   * 
   * <p>This method will quietly ignore missing or non-directory <code>baseDir</code>
   *  folder. 
   *
   * @param baseDir base directory whose children (either jars or directories of
   *                classes) will be in the classpath, will be resolved relative
   *                the instance dir.
   * @param filter The filter files must satisfy, if null all files will be accepted.
   * @param quiet  Be quiet if baseDir does not point to a directory or if no file is 
   *               left after applying the filter. 
   */
  void addToClassLoader(final String baseDir, final FileFilter filter, boolean quiet) {
    File base = FileUtils.resolvePath(new File(getInstanceDir()), baseDir);
    if (base != null && base.exists() && base.isDirectory()) {
      File[] files = base.listFiles(filter);
      if (files == null || files.length == 0) {
        if (!quiet) {
          log.warn("No files added to classloader from lib: "
                   + baseDir + " (resolved as: " + base.getAbsolutePath() + ").");
        }
      } else {
        this.classLoader = replaceClassLoader(classLoader, base, filter);
      }
    } else {
      if (!quiet) {
        log.warn("Can't find (or read) directory to add to classloader: "
            + baseDir + " (resolved as: " + base.getAbsolutePath() + ").");
      }
    }
  }