I am working on a functionality where i need to check whether database is down or not. i have to use single query which works for both oracle and sqlserver dbs. is there any single query which checks whether db is up or not?
similar to select * from dual;
Thanks!
I'd go with a connection.setAutoCommit(true) and not with a select.
I think it would be best to use the Connection's function to check the server is available.
There should be an Exception when it fails to connect and you can check the state to see if it's still open.
To address your specific need, if you decide to continue with a query.
THIS IS NOT BEST PRACTICE
I don't know of a simple way to do what you wish, Oracle and SQL don't share the same naming for system objects. BUT run that command, it won't work on SQL, but the exception won't be of type 'Server is Down' and you can use it in your try/catch.
THIS IS NOT BEST PRACTICE
Hope it makes sense.
Better way is to obtain the connection and then use the database metadata information like the product version or product name to ensure the database is up or not.
Eg:
try{
Con = DriverManager.getConnection(databaseURL,username,password);
databasemetadata = con.getMetaData();
String databaseName = databasemetedata.getDatabaseProductName();
If(databaseName.equals("<desireddabase>"))
{
//database up and running
}
}
catch(Exception e)
{
// error in connection ...
}
The java.sql.Connection has a method
isValid(timeOut)
Returns true if the connection has not been closed and is still valid. The driver shall submit a query on the connection or use some other mechanism that positively verifies the connection is still valid when this method is called.
Related
I'm trying to write a small code snippet where I need to get some data from a database and then process the result in some other java file. I tried writing a program and the execution for the same was failing with error "Cannot access resultset as the connection was already closed".
Is there any way can we store the result fetched from database some where (Ex.some arraylist) and use it for computation after closing the connection? If yes, can someone please explain it with example?
Slightly handicapped since I'm new to it.
Class A {
public Map<String, Object> loadDat(int acc,Map<String,Object> result)
throws Exception {
Class.forName("com.teradata.jdbc.TeraDriver");
Connection conn = DriverManager.getConnection(connectionString, user, password);
query = "select * from mytable where id="+acc;
PreparedStatement stmt = conn.prepareStatement(query);
ResultSet rs=stmt.executeQuery();
result.put(" Result", rs) ;
return result;
}
}
In general,
don't code JDBC database access by hand.
Libraries already exist that do all the low level JDBC handling now and
they do it correctly.
You will never do it better than an one of the mature,
open source projects already do it.
Instead,
learn and use something like MyBatis.
If you use Spring,
here is a link to the Mybatis-Spring project.
MyBatis conceals all of the data conversion and JDBC junk.
Instead, you define your query in a simple XML file and receive a List
as the result of a query.
Just to add to #DwB's answer that is correct.
You can 1) retrieve all rows from your query into a Java List, 2) then close the connection, and 3) then use the Java List in another class (for further processing).
If you close the connection after retrieving only part of the result set, you'll lose the rest of it and will receive the error you mention. Don't do it this way.
My connection string looks like this
String cn = "jdbc:odbc:DSN";
it works fine . However, when i try to modify it to
String cn = "jdbc:odbc:DSN, TYPE=FASTLOAD";
it does not establish connection
I also tried
String cn = "jdbc:odbc:DSN, TYPE=FASTLOADCSV";
Teradata's JDBC driver supports the FastLoad protocol, but you're not using it. You try to connect via JDBC-ODBC bridge, change to jdbc:teradata://...
Try
String cn = "jdbc:odbc:DSN; TYPE=FASTLOAD";
If you want to connect with ODBC, then use semicolons. But if you want to use FastLoad, then you need to connect using JDBC, in which case you should use commas and the forward slash like so:
String cn = "jdbc:teradata://servername/TYPE=FASTLOADCSV";
Also, you'll need to disable auto-committing whenever you fastload (at least if you do batch inserting, which you probably should). Fastload requires an empty table; committing causes the table to be non-empty. To prevent that issue, simply set autocommit to False before inserting, and set it back to True (or whatever you want it to be) after all inserts have been executed and committed.
Alternatively, you can pursue a different approach: commit stuff, but use staging tables. With this method you create new, empty tables for each insert batch. In the end you can consolidate those tables into one with the MERGE operation. If you do this process right, you can avoid any rewriting of data on disk. (Source: this other SO question)
More information:
Teradata JDBC tips on improving performance
Sample code from Teradata about JDBC, with boilerplate code on connectivity, CRUD, etc.
More Teradata docs on connectivity with JDBC
I need to define some variables in Oracle to be used further down our application's database installation scripts. Basically, the way our installer works now is it reads in the script files and calls each one via JDBC in Java. I need to have Oracle do the variable substitution on the database side, as there are procedures, triggers, create statements, etc. that will need to refer to them (So like "CREATE TABLE &&MYSCHEMA.TBL_NAME ...").
The problem I am having is that the DEFINE statement is throwing an error when calling it from Java (example):
private static void testDefineVariables() {
String url = "jdbc:oracle:thin:#localhost:1521:LOCALDEV";
String username = "SYSTEM";
String password = "manager42";
Connection conn = null;
Statement stmt = null;
try {
conn = DriverManager.getConnection(url, username, password);
stmt = conn.createStatement();
//Execute the sql
stmt.execute("DEFINE MYSCHEMA='TESTSCHEMA'");
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
finally {
try {
if(stmt != null)
stmt.close();
if(conn != null)
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
The error is:
java.sql.SQLSyntaxErrorException: ORA-00900: invalid SQL statement
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:439)
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:395)
at oracle.jdbc.driver.T4C8Oall.processError(T4C8Oall.java:802)
at oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:436)
at oracle.jdbc.driver.T4CTTIfun.doRPC(T4CTTIfun.java:186)
at oracle.jdbc.driver.T4C8Oall.doOALL(T4C8Oall.java:521)
at oracle.jdbc.driver.T4CStatement.doOall8(T4CStatement.java:194)
at oracle.jdbc.driver.T4CStatement.executeForRows(T4CStatement.java:1000)
at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:1307)
at oracle.jdbc.driver.OracleStatement.executeInternal(OracleStatement.java:1882)
at oracle.jdbc.driver.OracleStatement.execute(OracleStatement.java:1847)
at oracle.jdbc.driver.OracleStatementWrapper.execute(OracleStatementWrapper.java:301)
I am using an Oracle 11g R2 database with the ojdbc6-11.2.0.1.0.jar JDBC driver. I am able to execute the statement successfully from the sqldeveloper tool as well as the SQLPlus console, but not from the Java application. Do I need to configure additional properties on the database driver? Can I make this type of call from this driver?
I know some people right off the bat may suggest using variable bindings on the Java side, but this is not an option. The scripts need to be executable from both the SQL interface and the installer. There are other reasons apart from this one, which I won't go into.
I am also hoping to get this to work with the sql-maven-plugin, but that may not be possible based on this JIRA:
Add Oracle SQLPlus syntax for substitution variables
If anyone has any suggestions or know how to get this to work, I would greatly appreciate it.
I don't think DEFINE will work outside of SQLPLUS - JAVA uses JDBC
and assumes the argument to execute() is valid SQL. If you're able to
use DEFINE outside SQLPLUS it means the utility you're using is
intended to be compatible with or a partial replacement of SQLPLUS.
DEFINE is an SQLPLUS command - SQLPLUS is an ORACLE utility.
According to this URL Define is not an SQL statement
http://www.adp-gmbh.ch/ora/sqlplus/define.html
Both DEFINE and the substitution variable syntax &&MYSCHEMA.TBL_NAME are SQL*Plus commands. They are not valid SQL or PL/SQL constructs. You won't be able to use them as-is via JDBC.
Depending on the reasons that you say you don't want to go into
Your Java application can call out to the operating system to invoke SQL*Plus and pass in the script
Your Java application can implement whatever SQL*Plus features your scripts rely on. Rather than executing DEFINE MYSCHEMA='TESTSCHEMA', your application would need to maintain, say, a HashMap that maps a variable like myschema to a value like TESTSCHEMA. Your application would then have to parse the individual SQL statements looking for text like &&MYSCHEMA, replace that with the value from its local HashMap, and then send the resulting SQL string to the database server. Depending on how much of the SQL*Plus functionality you need to replicate, that could be a reasonably significant undertaking. Many PL/SQL IDEs (such as Toad or SQL Developer) implement a subset of SQL*Plus's functionality-- I don't know of any that have tried to implement every last SQL*Plus feature.
I need to connect to a remote database using Database link using JDBC commands.
How can it be done?
If you already have the dblink setup, you can utilize it in your SQL (sent via jdbc) by addressing the required tables like such:
select * from SCHEMA.TABLE#DBLINK_NAME
Using this query inside of your java would look something like this
public ResultSet execQuery() throws SQLException, ClassNotFoundException{
//Load the database driver
Class.forName("oracle.jdbc.OracleDriver");
//Create connection to the database
Connection myConnection = DriverManager.getConnection(connectURL,userName,userPwd);
//Create a statement link to the database for running queries
Statement myQuery = myConnection.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
//Create a resultSet to hold the returned query information
ResultSet myQueryResults = myQuery.executeQuery("select * from SCHEMA.TABLE#DBLINK_NAME");
return myQueryResults;
}
*java & oracle assumed
If you are asking about how to use JDBC to create a link between the DB you are talking to and another one, then it is "just SQL" that you (presumably) would execute in the same way as you would any other SQL statement. (If you tell us which DB you are using, we could talk about the actual SQL you need to execute.)
Otherwise, I don't think this makes sense. A DB link / Database link is a link from one database to another. But JDBC is for talking to a database from a Java client. It makes no sense (to me) to use DB link to connect a JDBC client to a database.
Please take a look at orajdbclink, on sourceforge
I am planning to to connect my oracle plsql sources to phoenix skin of hbase. It seems to me the unique way to create a connector between oracle and hbase for the moment...
Is there any way to get the Oracle query from PreparedStatement .I know its not possible as such I can't use log4jdbc or p6spy as it is a secured application and using this will create bigger problems..toString won't work as I am using Oracle? I can't change PreparedStatement to Statement either.
If only need for debug time then You can use DebuggableStatement follow this article
I don't think you should be doing it this way, as there is no officially documented API for this.
If you can mess with the code, why cannot you use log4jdbc ?
Oracle JDBC also supports java.util.logging, which you could try to enable.
If you are just interested in the SQL itself, you can turn on session tracing on the Oracle server.
Or maybe you can put your code to where the statement is being prepared (using something like #pinichi is suggesting)?
But just for fun, poking around with the debugger, with my version of Oracle JDBC, I can do
if (stmt instanceof oracle.jdbc.driver.OraclePreparedStatement) {
String x = ((oracle.jdbc.driver.OraclePreparedStatement) stmt)
.getOriginalSql();
System.out.println(x);
}
If you just want to check SQL statement you can also go straight to the database and check v$sql table.
There you can find all sqls and other information about query. More info: http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/dynviews_2113.htm