First of all, describe the project environment: Maven + mongodb-java-driver-3.2.2

The original project was written with Mongo 2. X driver, and then upgraded to 3. X. The first big change is user name and password verification.

This is the way to get mongoclient.

import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

import com.mongodb.MongoClient;
import com.mongodb.MongoClientURI;
import com.mongodb.MongoCredential;
import com.mongodb.ServerAddress;

/**
 * MongoDBUtils
 * @author administration
 *
 */
public class DBUtil {

	/**
	 * Connect to mongoDB with username password (MongoCredential method)
	 * @param mongodbAddr
	 * @param databaseName
	 * @return
	 */
	public static MongoClient getMongoClientByCredent(String mongodbAddr, String databaseName){
		MongoClient mongoClient;
		Properties p = TDTFile.getProperAddr("db.properties");
		String user = p.getProperty("username");
		String pswd = p.getProperty("password");
		List<ServerAddress> serverAddrList = new ArrayList<ServerAddress>();
		ServerAddress serverAddress = new ServerAddress(mongodbAddr);
		serverAddrList.add(serverAddress);
		List<MongoCredential> credentialList = new ArrayList<MongoCredential>();
		MongoCredential credential = MongoCredential.createCredential(user, databaseName, pswd.toCharArray());
		credentialList.add(credential);
		mongoClient = new MongoClient(serverAddrList, credentialList);
		return mongoClient;
	}
	
	/**
	 * Connect to mongoDB with username password (URI method)
	 * @param mongodbAddr
	 * @param databaseName
	 * @return
	 */
	public static MongoClient getMongoClientByURI(String mongodbAddr, String databaseName){
		MongoClient mongoClient;
		Properties p = TDTFile.getProperAddr("db.properties");
		String user = p.getProperty("username");
		String pswd = p.getProperty("password");
		//System.out.println(user + "," + pswd);
		String uri = String.format("mongodb://%s:%s@%s/%s", user, pswd, mongodbAddr, databaseName);
		System.out.println(uri);
		MongoClientURI mongoClientURI = new MongoClientURI(uri);
		mongoClient = new MongoClient(mongoClientURI);
		return mongoClient;
	}
	
}

Two ways are no problem, run well in eclipse. But!! After packaging with MVN package, it can’t be used. After a night and a day’s analysis, I locked the root cause of the error in the statement that the command line executed the command. My sentence is like this:

java -Djava.ext.dirs=../lib Other parameters

The problem lies in the – D parameter. Baidu knows that – D is equivalent to setting external environment variables. Since my main method relies on many third-party jar packages, it seems that there is nothing wrong with it. But it ignores a problem, that is

After using the – D parameter to specify other directories, Java needs to load% Java_ The jar package in the home% \ JRE/lib/ext directory is no longer loaded!! I searched the usage of – D parameter on the Internet for a long time, but no one mentioned it.. But it’s hard for me. One day is wasted here..

Solution:

Package the required external dependent packages, including some packages such as JDK’s own encryption algorithm, into lib with Maven. Problem solving. By the way, the algorithm package required by mongodb3. X is% Java_ HOME%\jre\lib\ext\sunjce_ provider.jar