change database name from string literal to a static final variable DATABASE_NAME

Author: mashuai

src/main/java/edu/uci/ics/crawler4j/frontier/Counters.java

@@ -47,6 +47,7 @@ public static class ReservedCounterNames {
     public static final String PROCESSED_PAGES = "Processed-Pages";
   }
 
+  private static final String DATABASE_NAME = "Statistics";
   protected Database statisticsDB = null;
   protected Environment env;
 
@@ -70,7 +71,7 @@ public Counters(Environment env, CrawlConfig config) {
       dbConfig.setAllowCreate(true);
       dbConfig.setTransactional(true);
       dbConfig.setDeferredWrite(false);
-      statisticsDB = env.openDatabase(null, "Statistics", dbConfig);
+      statisticsDB = env.openDatabase(null, DATABASE_NAME, dbConfig);
 
       OperationStatus result;
       DatabaseEntry key = new DatabaseEntry();

src/main/java/edu/uci/ics/crawler4j/frontier/DocIDServer.java

@@ -37,6 +37,7 @@
 
 public class DocIDServer extends Configurable {
 
+  private static final String DATABASE_NAME = "DocIDs";
   protected static final Logger logger = LoggerFactory.getLogger(DocIDServer.class);
 
   protected Database docIDsDB = null;
@@ -51,7 +52,7 @@ public DocIDServer(Environment env, CrawlConfig config) {
     dbConfig.setAllowCreate(true);
     dbConfig.setTransactional(config.isResumableCrawling());
     dbConfig.setDeferredWrite(!config.isResumableCrawling());
-    docIDsDB = env.openDatabase(null, "DocIDs", dbConfig);
+    docIDsDB = env.openDatabase(null, DATABASE_NAME, dbConfig);
     if (config.isResumableCrawling()) {
       int docCount = getDocCount();
       if (docCount > 0) {

src/main/java/edu/uci/ics/crawler4j/frontier/Frontier.java

@@ -36,7 +36,7 @@
 public class Frontier extends Configurable {
 
   protected static final Logger logger = LoggerFactory.getLogger(Frontier.class);
-
+  private static final String DATABASE_NAME = "PendingURLsDB";
   protected WorkQueues workQueues;
 
   protected InProcessPagesDB inProcessPages;
@@ -54,7 +54,7 @@ public Frontier(Environment env, CrawlConfig config) {
     super(config);
     this.counters = new Counters(env, config);
     try {
-      workQueues = new WorkQueues(env, "PendingURLsDB", config.isResumableCrawling());
+      workQueues = new WorkQueues(env, DATABASE_NAME, config.isResumableCrawling());
       if (config.isResumableCrawling()) {
         scheduledPages = counters.getValue(Counters.ReservedCounterNames.SCHEDULED_PAGES);
         inProcessPages = new InProcessPagesDB(env);

src/main/java/edu/uci/ics/crawler4j/frontier/InProcessPagesDB.java

@@ -40,9 +40,9 @@
 public class InProcessPagesDB extends WorkQueues {
 
   private static final Logger logger = LoggerFactory.getLogger(InProcessPagesDB.class);
-
+  private static final String DATABASE_NAME = "InProcessPagesDB";
   public InProcessPagesDB(Environment env) {
-    super(env, "InProcessPagesDB", true);
+    super(env, DATABASE_NAME, true);
     long docCount = getLength();
     if (docCount > 0) {
       logger.info("Loaded {} URLs that have been in process in the previous crawl.", docCount);