Make your Mysql friendly to Emoji character

In my last projects, Mysql is usually UTF-8 as the core encoding. However, it is not good for my current project now because we will play with Emoji Character;

Emoji Character is using an extended utf-8 Encoding, called UTF-8 mb4 (utf8mb4).

If inserting string with Emoji Character, the mysql will alert "incorrect string" and make the SQL fail.
To fix this, we need to:

• Change the database and table to utf8mb4 encoding 
• Change the connection encoding to utf8mb4 as well

External Reference:

• http://mathiasbynens.be/notes/mysql-utf8mb4
• http://info.michael-simons.eu/2013/01/21/java-mysql-and-multi-byte-utf-8-support/
• http://my.oschina.net/wingyiu/blog/153357

Abnormal java.net.UnknownHostException on resin

Recently, I encountered a problem while I am calling to Google API in my java code running on Resin. The problem is that: The http call raise an UnknownHostException;

It doesn't caused by Java itself because the UnitTest show it is correct.
It doesn't caused by Resin because it work in my development platform.

So what go wrong? Finally, I has discovered it is wrong in the staging server environment;
The /etc/hosts isn't configured as the resin want to. (... maybe it is the problem of resin too ..)

To fix it:
- type "hostname" to find your hostname . e.g "my.pc"
- edit /etc/hosts and add the line "127.0.0.1 my.pc"
- restart the server to make it effective

Notes:
- This problem may not be happened in all environment. My macbook doesn't have the problem.

Related Links:

• http://ajia.github.io/blog/2013/03/11/yu-dao-resin-com-dot-caucho-dot-config-dot-configruntimeexception-java-dot-net-dot-unknownhostexception/
• http://forum.caucho.com/showthread.php?p=35348

Make java connection pool auto reconnect

Recently we encountered a problem when using java db connection pool. The problem is that the connection is being closed by the DB server since it is already timeout. To due with this, need to configure two more parameters.

They are:
- testOnBorrow  ;  define it as "true"
- validationQuery ; define it as "SELECT 1 FROM dual" if you are also using MySQL

Yes, It is easy to config it. But how to test it? (Many sites may not give the answer). 

To verify the configuration is work, we can make a simple Unit Test;

Step 1: Make a failure case

Make an unit test base on the following code;


Properties p = new Properties(); 
prop.put("driver", "org.gjt.mm.mysql.Driver");
prop.put("url", "jdbc://localhost:3306/db");
prop.put("username", "user");
prop.put("password", "123456");
p.setProperties("testOnBorrow", "false");
p.setProperties("validationQuery", "");

BasicDataSource ds = BasicDataSourceFactory.createDataSource(prop);
ds.setMaxActive(1);
ds.setMaxIdle(1);
ds.setMinIdle(0);

Connection conn = ds.getConnection();
System.out.println("First connection");


System.out.println("Sleep start");
Thread.sleep(10000);
System.out.println("Sleep end");

Connection conn = ds.getConnection();
System.out.println("Second connection");


To make the connection fail at the second time, try to kill the connection in DB side while "Thread.sleep";


Step 2: Fix the failure 

Simply change "testOnBorrow=false" and "validationQuery=" to 
 "testOnBorrow=true" and "validationQuery=SELECT 1 FROM dual"

Then, run the test again. we will see "Second connection" show up instead of Exception message.