google-guice example

Google-Guice:

Is a java framework to provide dependency injection (DI).

Basic advantages:

Your code will be easier to change, unit test and reuse in other contexts.

Official link:

http://code.google.com/p/google-guice/

My example:

public class AllInOne {

public interface DemoInt {

public String test();

}

public static class DemoImp implements DemoInt {

public String test() {

return "OK";

}

}

public static class Demo {

@Inject

private DemoInt injectedClass;

public String makeTest() {

return injectedClass != null ? injectedClass.test() : "ERROR";

}

}

public class DemoModule extends AbstractModule {

@Override

protected void configure() {

bind(DemoInt.class).to(DemoImp.class);

}

}

public AllInOne() {

Injector injector = Guice.createInjector(new DemoModule());

Demo demo = injector.getInstance(Demo.class);

System.out.println(demo.makeTest());

}

public static void main(String a[]) {

new AllInOne();

}

}

Communications link failure between MySQL and Hibernate after many hours

The Problem:

I was using hibernate and MySql with apache-commons-dhcp. At the beginning everything works ok, but usually the first user who tray to login in the application in the morning get this exception:

2010-02-25 10:58:15,855 ERROR [org.hibernate.transaction.JDBCTransaction] - JDBC begin failed

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 10.228 milliseconds ago. The last packet sent successfully to the server was 16 milliseconds ago.

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)

Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.

at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2497)

at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2949)

... 47 more

25-feb-2010 10:58:15 org.apache.catalina.core.StandardWrapperValve invoke

GRAVE: Servlet.service() para servlet default lanzó excepción

org.springframework.transaction.CannotCreateTransactionException: Could not open Hibernate Session for transaction; nested exception is org.hibernate.TransactionException: JDBC begin failed:

at org.springframework.orm.hibernate3.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:599)

at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:374)

at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:263)

at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:101)

Caused by: org.hibernate.TransactionException: JDBC begin failed:

at org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:68)

at org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1326)

at org.springframework.orm.hibernate3.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:558)

... 36 more

Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 10.228 milliseconds ago. The last packet sent successfully to the server was 16 milliseconds ago.

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)

at java.lang.reflect.Constructor.newInstance(Constructor.java:513)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)

Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.

at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2497)

at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2949)

... 47 more

The Cause:

MySQL server has a default timeout period after which it terminates the idle connections.

This period is 8 hours by default.

Searching on the Internet I found many solutions:

• Disable SQL_CACHE on mysql (http://forums.mysql.com/read.php?39,203407,217196#msg-217196)
• Use c3p0 in hibernate (http://hibernatedb.blogspot.com/2009/05/automatic-reconnect-from-hibernate-to.html)
• Many others..

But always looks a big change in the application for a simple problem, finally

The Solution:

Add the following properties to dbcp configuration:

• validationQuery=”SELECT 1″
• testOnBorrow=”true”

How it Works:

• validationQuery --> Before returning the connection from pool to the application, dbcp runs the “SELECT 1 ” query on the connection to see it it is still live.
• testOnBorrow --> you tell dbcp to perform the check before returning the connection to application.

Other link with the same solution:

http://amitcodes.wordpress.com/2008/07/26/16/

IE6 + HTTPS + download files = bug

The problem:

When you try to download a file using href tag in a HTTPS connection with Internet Explorer 6 you get this error: "Internet Explorer Cannot Download".

The Microsoft support link: http://support.microsoft.com/kb/812935/

My initial HTML code:

<a href="../files/test.zip">download</a>

The solution:

Make a specific "servlet" to perform the download. And change there the cache parameters in the request.

The official support says that error hapen with IE6 SP1 but I get the same situation with IE6 SP2.

<html>

<head>

<%@page import="java.util.*,java.io.*, javax.activation.MimetypesFileTypeMap"%>

<%@ page language="java" session="false" contentType="text/html; charset=8859_1"%>

</head>

<body>

<%

String fileName=request.getParameter("fileName");

File f=new java.io.File(request.getRealPath("/ficheros")+"/"+fileName);

if(!f.exists()){

%>

<script>alert("Error: Fichero ['<%=fileName%>'] inexistente!");</script>

<%

}else{

//the content type set as excel

response.setContentType (new MimetypesFileTypeMap().getContentType(f));

//the header and also the Nameis set by which user will be prompted to save

response.setHeader ("Content-Disposition", "attachment;filename="+fileName);

response.setHeader("Content-Disposition", "inline; filename="+fileName);

response.setHeader("Expires", "0");

//response.setHeader("Cache-Control", "must-revalidate, post-check=0,pre-check=0");

response.setHeader("Pragma", "public");

// response.setDateHeader("Expires", 0); //prevents caching at the proxy

response.setHeader("Cache-Control", "max-age=0");

InputStream isStream = null;

ServletOutputStream sosStream = null;

try{

//response.flushBuffer();

isStream = new java.io.FileInputStream(f);

sosStream = response.getOutputStream();

int ibit = 256;

while ((ibit) >= 0){

ibit = isStream.read();

sosStream.write(ibit);

}

}catch (java.lang.Exception ioeException){%>

<script>alert('Se ha producido un error inesperado.!');</script>

<%}

sosStream.flush();

sosStream.close();

isStream.close();

}

%>

</body>

</html>

Now works with all browsers without errors.