Monday, March 28, 2011

OSGi bootdelegation

I found a situation where an osgi bundle made a reference to an expected system library that wasn't there, but since the bundle did not include the dependency as an osgi reference, the framework (Felix in this case) threw a 'Class Not Found' exception.

Turns out, our friends at the OSGi Alliance have a solution for this kind of problem.

org.osgi.framework.bootdelegation=package

Essentially, packages specified will bypass the osgi environment and go directly to the VM.

Seems like this feature should be used sparingly and only when necessary.

MongoDB Shell Command Reference

Good reference for MongoDB shell commands:
http://www.mongodb.org/display/DOCS/dbshell+Reference

Debugging Pax-Runner Applications

Include as flag passed into paxrunner.jar

--vmOptions="-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=5005"

In IDE start a remote debugging session and use port 5005.

Sunday, March 27, 2011

Sample Java usage for MongoDB

Maven

<dependency>
<groupId>org.mongodb</groupId>
<artifactId>mongo-java-driver</artifactId>
<version>2.5</version>
</dependency>

Connect to Mongo

import com.mongodb.DB;
import com.mongodb.Mongo;

//...

Mongo mongo = new Mongo(host, 27017);
DB db = mongo.getDB("name of db"); //If db does not exist, then it will be created.

Insert JSON Data

import com.mongodb.BasicDBObject;
import com.mongodb.DBCollection;

//...

DBCollection coll = db.getCollection("testCollection"); //If collection does not exist, then it will be created.
BasicDBObject doc = new BasicDBObject();
doc.put("hello", "world");

BasicDBObject inner = new BasicDBObject();
inner.put("key","value");
doc.put("inner", inner);

coll.insert(doc);

Fetch JSON Data

import com.mongodb.BasicDBObject;
import com.mongodb.DBCollection
import com.mongodb.DBCursor;

//...

DBCollection coll = db.getCollection("testCollection");
BasicDBObject query = new BasicDBObject();
query.put("hello", "world");
DBCursor cursor = coll.find(query);
while(cursor.hasNext()) {
System.out.println(cursor.next());
}

GridFS

import com.mongodb.gridfs.GridFS;

//...

GridFS fs = new GridFS(db, "collection"); //If bucket does not exist, it will be created.

GridFS Save File

import java.io.File;
import com.mongodb.gridfs.GridFSInputFile;

//...

GridFSInputFile file = fs.createFile(new File("/path/to/file.ext"));
file.save();

GridFS List Files

import com.mongodb.DBCursor;

//...

DBCursor cursor = fs.getFileList();
while(cursor.hasNext()) {
System.out.println(cursor.next());
}

GridFS Read File

GridFSDBFile file = fs.findOne("file.ext");
BufferedReader reader = new BufferedReader(new InputStreamReader(file.getInputStream()));
String line = null;
while((line = reader.readLine()) != null){
System.out.println(line);
}

Map/Reduce

Example Dataset:
{ "_id" : ObjectId("4d8233d6d638a2ca105b1fab"), "name" : "John", "number" : 2 }
{ "_id" : ObjectId("4d8233d6d638a2ca105b1fac"), "name" : "Jane", "number" : 2 }
{ "_id" : ObjectId("4d8233dbd638e40a183d27f8"), "name" : "John", "number" : 2 }
{ "_id" : ObjectId("4d8233dcd638e40a183d27f9"), "name" : "Jane", "number" : 2 }

Code Example:
import com.mongodb.MapReduceCommand;
import com.mongodb.MapReduceOutput;

//...

String map = "function(){" +
"emit(this.name, {count: 1, sum: this.number});" +
"};";

String reduce = "function( key , values ){" +

"var n = { count: 0, sum: 0}; " +

"for ( var i = 0; i < values.length; i ++ ) {" +

"n.sum += values[i].sum;" +

"n.count += values[i].count;" +

"};" +

"return n;" +

"};";

MapReduceOutput out = coll.mapReduce(map, reduce, null, MapReduceCommand.OutputType.INLINE, null);
for ( DBObject obj : out.results() ) {
System.out.println( obj );
}

Expected Output:
{ "_id" : "Jane" , "value" : { "count" : 2.0 , "sum" : 4.0}}
{ "_id" : "John" , "value" : { "count" : 2.0 , "sum" : 4.0}}

Execute Shell Commands in Ruby

There are 3 ways in Ruby to execute Shell commands, each does it a little differently.

exec 'command'
This will execute the command and exit the Ruby script.

system 'command'
This will execute the command but you have no way to access the results. You will simply get a true or false indicating if the command was able to be executed. Call $? to get more information on the exit conditions

`command`
This will execute the command and give you access to any returned strings.

Create Class Dynamically in Ruby

Sample

def create_class_dynamically(mybinding)
clazz = 'class MyClass; end'
Kernel.eval(clazz, mybinding)
end

create_class_dynamically(binding)

Connect to SOAP Server in Ruby

Simple Example

require 'soap/wsdlDriver'

def self.remote_wsdl(url)
wsdl = SOAP::WSDLDriverFactory.new(url)
begin
return wsdl.create_rpc_driver
rescue
return wsdl.create_driver
end
end

tar - Archive contains obsolescent base-64 headers

Problem:
> tar -xvf myfile.tar.gz
tar: This does not look like a tar archive
tar: Skipping to next header
tar: Archive contains obsolescent base-64 headers
tar: Error exit delayed from previous errors

Resolution:
> gzip -d myfile.tar.gz
> tar -xf myfile.tar

Open Port in Redhat

Instructions

nano /etc/sysconfig/iptables
Insert the following line with the desired port number (in this case, replace 22 with desired port)
- -A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
Save and close the file
/etc/init.d/iptables restart

Eclipse Setup

In Eclipse's Debug Perspective, click on the Run -> Debug Configurations menu
Find "Remote Java Application" and then click New and fill out the information

Virgo Setup

Start the server using the "-debug" & "-suspend" attributes

Magic

Start Virgo, then start the configuration in Eclipse
It may ask you to associate the code before step threw can happen, simply choose the code in your workspace that is appropriate.

<dependencies>
<dependency>
<groupId>org.ops4j.pax.runner</groupId>
<artifactId>pax-runner</artifactId>
<version>${pax-runner.version}</version>
<scope>provided</scope>
</dependency>
</dependencies>

<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.2.1</version>
<executions>
<execution>
<id>create-target</id>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
<configuration>
<descriptors>
<descriptor>src/main/etc/assembly/paxrunner-assembly.xml</descriptor>
</descriptors>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>

The assembly file will tell Maven how to package the final output. The xml is fairly easy to read, see the maven-assembly-plugin documentation for specifics. The one thing worth calling out is the exclusion of the spring and related libraries, this is because pax-runner already has a built in profile that will download and wire them up properly.

paxrunner-assembly.xml

<assembly xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.2 http://maven.apache.org/xsd/assembly-1.1.2.xsd">

<id>distribution</id>

<formats>
<format>dir</format>
<format>zip</format>
</formats>

<includeBaseDirectory>false</includeBaseDirectory>

<files>
<file>
<source>src/main/etc/scripts/run.sh</source>
<fileMode>0777</fileMode>
</file>
<file>
<source>src/main/etc/scripts/run.bat</source>
<fileMode>0777</fileMode>
</file>
</files>

<moduleSets>
<moduleSet>
<binaries>
<unpack>false</unpack>
<includeDependencies>true</includeDependencies>
<outputDirectory>lib/module-bundles</outputDirectory>
<dependencySets>

<dependencySet>
<outputDirectory>lib/required-bundles</outputDirectory>
<excludes>
<exclude>org.springframework:org.springframework.core</exclude>
<exclude>org.springframework:org.springframework.aop</exclude>
<exclude>org.springframework:org.springframework.asm</exclude>
<exclude>org.springframework:org.springframework.beans</exclude>
<exclude>org.springframework:org.springframework.context</exclude>
<exclude>org.springframework:org.springframework.context.support</exclude>
<exclude>org.springframework:org.springframework.expression</exclude>
<exclude>org.slf4j:*</exclude>
<exclude>org.aopalliance:*</exclude>
<exclude>org.apache.commons:*.logging</exclude>
</excludes>
</dependencySet>
</dependencySets>
</binaries>
</moduleSet>
</moduleSets>

<dependencySets>

<dependencySet>
<scope>provided</scope>
<includes>
<include>org.ops4j.pax.runner:pax-runner</include>
</includes>
<outputFileNameMapping>${artifact.artifactId}.${artifact.extension}</outputFileNameMapping>
</dependencySet>
</dependencySets>

</assembly>

Finally for the scripts, these do nothing more than start up pax-runner and pass in any directories of bundles or configuration files.

run.sh

java -jar pax-runner.jar --profiles=spring.dm --workingDirectory=. scan-dir:lib/required-bundles scan-dir:lib/module-bundles

run.bat

@echo off
call java -jar pax-runner.jar --profiles=spring.dm --workingDirectory=. scan-dir:lib/required-bundles scan-dir:lib/module-bundles %1 %2 %3

Adventures in Software Engineering