我是MongoDB的初学者，正在尝试一些东西。 我想要存储URL并避免重复的URL，因此我在url上创建了一个唯一索引。 就像这样：
collection.createIndex(new BasicDBObject("url", type).append("unique", true));
但是每次我启动程序时，索引都会被重新创建，是吗？
因为现在我的程序只插入一个url "http://site.com"，如果我重新启动程序，这个url会再次插入，就好像没有索引一样。
每次创建索引是处理索引的错误方式吗？
这是我的代码示例：
mongo.getCollection().ensureIndex(new BasicDBObject("url", 1).append("unique", "true"));
mongo.getCollection().insert(new BasicDBObject("url", "http://site.com").append("crawled", 0));
mongo.getCollection().insert(new BasicDBObject("url", "http://site.com").append("crawled", 0));
输出结果为：
{ "_id" : { "$oid" : "50d627cf44ae5d6b5e9cf106"} , "url" : "http://site.com" , "crawled" : 0}
{ "_id" : { "$oid" : "50d627cf44ae5d6b5e9cf107"} , "url" : "http://site.com" , "crawled" : 0}
谢谢
编辑：
这是我的Mongo类，用于处理MongoDB import java.net.UnknownHostException; import java.util.List; import java.util.Set;
import com.mongodb.BasicDBObject; import com.mongodb.DB; import com.mongodb.DBCollection; import com.mongodb.DBObject; import com.mongodb.MongoClient;
public class Mongo {
private MongoClient mongoClient;
private DB db;
private DBCollection collection;
private String db_name;
public Mongo(String db){
try {
mongoClient = new MongoClient( "localhost" , 27017 );
this.db = mongoClient.getDB(db);
this.db_name = db;
} catch (UnknownHostException e) {
e.printStackTrace();
}
}
public void drop(){
mongoClient.dropDatabase(db_name);
}
public void listCollections(){
Set<String> colls = db.getCollectionNames();
for (String s : colls) {
System.out.println(s);
}
}
public void listIndex(){
List<DBObject> list = collection.getIndexInfo();
for (DBObject o : list) {
System.out.println("\t" + o);
}
}
public void setCollection(String col){
this.collection = db.getCollection(col);
}
public void insert(BasicDBObject doc){
this.collection.insert(doc);
}
public DBCollection getCollection(){
return collection;
}
public void createIndex(String on, int type){
collection.ensureIndex(new BasicDBObject(on, type).append("unique", true));
}
}
这是处理程序的类：
public class Explorer {
private final static boolean DEBUG = false;
private final static boolean RESET = false;
private Mongo mongo;
private String host;
public Explorer(String url){
mongo = new Mongo("explorer");
mongo.setCollection("page");
if (RESET){
mongo.drop();
System.out.println("Set RESET to FALSE and restart the program.");
System.exit(1);
}
if (DEBUG) {
mongo.listCollections();
}
this.host = url.toLowerCase();
BasicDBObject doc = new BasicDBObject("url", "http://site.com").append("crawled", 0);
mongo.getCollection().ensureIndex(new BasicDBObject("url", 1).append("unique", true));
mongo.getCollection().insert(new BasicDBObject("url", "http://site.com").append("crawled", 0));
mongo.getCollection().insert(new BasicDBObject("url", "http://site.com").append("crawled", 0));
process();
}
private void process(){
BasicDBObject query = new BasicDBObject("crawled", 0);
DBCursor cursor = mongo.getCollection().find(query);
try {
while(cursor.hasNext()) {
System.out.println(cursor.next());
}
} finally {
cursor.close();
}
}
}