Develop Reference

H2 Client couldn't connect to the server

I am trying to connect to H2 Server started on the same machine using java. I started the H2 server in mixed mode. While connecting to the server I am getting Error.
The code to start the server is:
Server.createTcpServer("-tcp", "-tcpAllowOthers", "-tcpSSL").start();
The code to connect to the server is:
Class.forName("org.h2.Driver");
Connection conn = DriverManager.getConnection("jdbc:h2:tcp://127.0.0.1/~/Data/test", "", "");
The Error is:
Connection is broken: "unexpected status 352518912" [90067-197]
Anybody please help me with this. I am stuck at this for two days.

You need to use ssl protocol instead of tcp in the URL, because you use an encrypted socked on the server.
"jdbc:h2:ssl://127.0.0.1/~/Data/test"
Please also note that database cannot be created remotely by default in recent versions of H2 due to security reasons. You need to create the database on the server side with a local url such as "jdbc:h2:~/Data/test", it's enough to open and close a connection to it.
Also I hope that empty password is only for that example code in the question. If you have a database that has an user with ADMIN privileges (username and password from the first connection that creates the database are used to create such user) and an empty or weak password (or if you enable the remote database creation), anyone, who can connect to that port, will get full access to your server process and this process most likely already has the same access to your system as you, so you effectively create a remote security hole with -tcpAllowOthers and such passwords.

Unable to connect Java application to SQL Server database

I am trying to write a Java desktop app that can connect to my database made with Microsoft SQL Server Manager to allow me to view and update it. But, I am having trouble getting the connection to work. I've read through a bunch of tutorials and threads here on Stack Exchange of similar problems, and I'm not sure what I'm doing wrong.
The server is called "SQLEXPRESS" using Windows authentication. I downloaded the JDBC driver found here: https://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=11774 installed it in NetBeans by going to "Services-Databases(right click)-New Connection-Add", but I also added it as a library in my project.
When I try this code, I get the exception that the TCP/IP connection failed either because the server isn't running or port 1433 is locked:
try{
String
URL="jdbc:sqlserver://sqlexpress:1433;DatabaseName=GreenhouseManagement";
Connection conn = DriverManager.getConnection(URL,"","");
System.out.println("connected");
}catch(Exception e){
System.out.println("Oops\n"+e);
}
What do I need to change to fix this?

You might need to reconfigure your connection string into this format.
jdbc:microsoft:sqlserver://HOST:1433;DatabaseName=DATABASE
HOST in this case is most likely to be "localhost" since you are connecting on a local machine.
DATABASE will be the name of your database
Reference: http://alvinalexander.com/java/jdbc-connection-string-mysql-postgresql-sqlserver

Exception while connecting to DB2 in java using JDBC

I am trying to connect to a db2 database in Java. Below the driver and the connection string and the driver details i am giving
Class.forName("COM.ibm.db2.jdbc.net.DB2Driver");
String url="jdbc:db2://hostname:portnumber/databasename";
sourceConnection=DriverManager.getConnection(url,"username","password");
But I am getting the below exception
"COM.ibm.db2.jdbc.DB2Exception: [IBM][JDBC Driver] CLI0615E Error receiving from socket, server is not responding. SQLSTATE=08S01"
I also tried changing the connection string to
String url="jdbc:db2:hostname:portnumber/databasename";
Still it is resulting the same exception above while trying to get the Connection.
And i have tried the below option also using JDBC app driver
Class.forName("COM.ibm.db2.jdbc.app.DB2Driver");
DB2DataSource db2ds = new DB2DataSource();
db2ds.setServerName("hostname");
db2ds.setPortNumber(portnumber);
db2ds.setDatabaseName("databasename");
db2ds.setUser("username");
db2ds.setPassword("password");
sourceConnection=db2ds.getConnection();
For the above two connection I used the jar "db2java.jar"
And i have tried using the JCC driver:
Class.forName("com.ibm.db2.jcc.DB2Driver");
String url="jdbc:db2://hostname:portnumber/databasename";
sourceConnection=DriverManager.getConnection(url,"username","password");
For this connection i have added the below jars
1)db2jcc.jar
2)db2jcc_license_cu.jar
This time around I am getting the below error,
"com.ibm.db2.jcc.am.go: [jcc][t4][201][11237][3.57.82] Connection authorization failure occurred.
Reason: Security mechanism not supported. ERRORCODE=-4214, SQLSTATE=28000"
I tried to connect to the same db2 source using "Quest for DB2" tool and the connection was successful.
Am i missing something in the code and is it a problem with DB2 drivers or connection string?
Can someone please guide me.
Thanks in advance.

Cause:
If the DB2® instance where InfoSphere Optim Performance Manager is running has the authentication configuration parameter set to DATA_ENCRYPT, you cannot log in to the web console.
Resolving the problem:
Do the following steps:
On the DB2 instance where Optim Performance Manager is running, set the authentication configuration parameter to SERVER by issuing the following command:
db2 update dbm cfg using authentication server
Restart the DB2 instance and InfoSphere Optim Performance Manager.
For more details visit here.

Your first two attempts were not supposed to work. You're using the JCC driver URL format, so it wouldn't be valid for either "net" or "app" drivers, which are deprecated anyway.
Use the JCC driver (com.ibm.db2.jcc.DB2Driver) and the URL format of "jdbc:db2://hostname:portnumber/databasename" and see this technote for the solution to the "Security mechanism not supported" problem. In short, you need to use a supported JDK.

Problem in establishing DB2 connection in Java with wrong username/password

I have a problem in establishing DB2 connection with wrong user-name/password. We have an application which runs on LAN on many systems using DB2 database located on my system as well as other systems.
Firstly I use this URL to create other system DB2 connection:
Connection con = DriverManager.getConnection("jdbc:db2://Rahulkcomputer:50000/XAN4", "rahulk", "dbirs#35");
this returns proper Connection object. Now when I change the URL to access my system DB2 connection with same user-name/password as (using same user-name/password is intensely done for checking error handling):
Connection con = DriverManager.getConnection("jdbc:db2://127.0.0.1:50000/XAN4", "rahulk", "dbirs#35");
This time it again returns the Connection object instead of throwing an SQLException specifying wrong user-name/password (due to my system's DB2 authentication is totally different from Rahulkcomputer's system)
After getting connection, I execute this query to check proper user name as explained in post:
Simple DB2 Query for connection validation
SELECT CURRENT SQLID FROM SYSIBM.SYSDUMMY1
(this returns "rahulk" in both cases)
Why DB2 created connection in 2nd case with wrong user-name/password (moreover when we close all the services of DB2 on Rahulkcomputer, even then I get the connection in 2nd case)?
Thanks in Advance.

You either created your database with the restrictive option or revoked the select right to sysibm from PUBLIC. The connection you had was fine, the access rights not. 42704 is DB2's way of saying "huh?", it did not recognize sysibm because you had no rights to see it.

Connecting to local instance of PostgreSql with JDBC

I have a running local instance of PostgreSql on a linux machine. When I use psql command from the shell I success to log in without any problem. I need to connect to the PostgreSql via the JDBC, but I don't know what exactly should I pass as url parameter to DriverManager.getConnection().
It should start with jdbc:postgresql: but what's going next?
I was told by the system group that a database with was created like user name. e.g. if my user is jutky a db named jutky was created, but when I try to open a connection to jdbc:postgresql:jutky I get an error
org.postgresql.util.PSQLException: FATAL: password authentication failed for user "jutky"
:(
Additional info
When I login via the psql I'm not prompted for the password, so when I try to login via JDBC I pass an empty string as a password - is it correct, or should I pass null or something?
When I type psql --help in the shell I see among the rest this line:
Connection options:
-h, --host=HOSTNAME database server host or socket directory (default: "/var/run/postgresql")
So I understand that I connect to PostgreSql via a socket directory, does that matters something to the URL string in the JDBC?
EDIT
First thanks for the answers.
Second: its not first time I'm using JDBC and in particular not the first time I'm connecting to the PostgreSql from JDBC, so I know the general rules and I have read the documentations. However in the described case I'm not sure how exactly should I construct the connection string if the instance is running via the socket directory and what password should I provide. Because when I login via the psql I'm not prompted for password at all.
Thanks in advance.

In addition to other answers note that by default Postgres is configured to accept connections via Unix sockets with authentication based on your operating system account, that's why psql works fine and doesn't require the password.
JDBC connections are made over TCP/IP with password authentication, so you need to modify pg_hba.conf accordingly. For example, this line allows TCP/IP connections from the same machine to all databases for all users with password authentication:
host all all 127.0.0.1/32 md5
After adding this line jdbc:postgresql:databasename should work.
EDIT: You can't create a JDBC connection over Unix socket since PostgreSQL JDBC driver can only work over TCP/IP. The password you use when creating JDBC connection is the password assigned to your user. If you don't have it, you can assign it, for example, using ALTER USER command. See 19.3. Authentication methods.
See also:
19.1. The pg_hba.conf file

It's all explained in official documentation.
This is the relevant part:
String url = "jdbc:postgresql://localhost/test?user=fred&password=secret&ssl=true";
Connection conn = DriverManager.getConnection(url);