If you have any suggestion or feedback, don’t hesitate to drop me a line

Build & Install

It is very easy to build from source code with maven:

1. git clone https://github.com/duydo/jpa-repository.git
2. cd jpa-repository
3. mvn install

If you use maven with project, just adding dependency to your pom, :

<dependency>
<groupId>com.duydo</groupId>
<artifactId>jpa-repository</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>

Usage

Create an example entity User

    @Entity
    public class User extends EntityObject {
        private String name;
        private Integer age;
        private String email;

        public User() {}
        //getter/setter here

    }

First, we need to create an instance of Repository

EntityManager em = ...;
Repository repo = new JPARepository(em);

Basic Query

//find all users
List users = repo.findAll(User.class)

//find user by id
User user = repo.findById(User.class, 1L);

//create
User user = new User();
repo.save(user);

//update
User user = repo.findById(User.class, 1L);
user.setName("Duy Do");
repo.update(user);

// delete
repo.remove(user);

Query with Specification

Find unique user has email abc@example.com

Specification hasEmail = Specifications.equal("email", "abc@example.com");
User user = repo.findBySpecification(User.class, hasEmail).asSingle();

Find all users has name “Duy”

Specification hasName = Specifications.equal("name", "Duy");
List users = repo.findBySpecification(User.class, hasName).asList();

Find all users which name is not “Duy”

Specification notName = Specifications.equal("name", "Duy").not();
List users = repo.findBySpecification(User.class, notName).asList();

We can combine specifications with AND, OR

//Find users has name "Duy" and age is "28"
Specification hasName = Specifications.equal("name", "Duy");
Specification hasAge28 = Specifications.equal("age", 28);
List users = repo.findBySpecification(User.class, hasName.and(hasAge28)).asList();

Sorting

Sorting by using method sortXXX() of SepecificationResult

Find all users has name “Duy” and sort ascending by name

Specification hasName = Specifications.equal("name", "Duy");
List users = repo.findBySpecification(User.class, hasName).sortAscending("name").asList();

Paging

Paging by using method skip(int count) and get(int count) of SepecificationResult

Find 10 users has name “Duy”

Specification hasName = Specifications.equal("name", "Duy");
List users = repo.findBySpecification(User.class, hasName).get(10).asList();

Find all users has name “Duy” but skip 10 first users

Specification hasName = Specifications.equal("name", "Duy");
List users = repo.findBySpecification(User.class, hasName).skip(10).asList();

Find 20 users has name “Duy” but skip 10 first users

Specification hasName = Specifications.equal("name", "Duy");
List users = repo.findBySpecification(User.class, hasName).skip(10).get(20).asList();

First, ensure JDK 1.6 installed on your system and set environment variable JAVA_HOME point to jdk path and then following these steps:

Install

1. Download and install CDH4 repository

wget http://archive.cloudera.com/cdh4/one-click-install/precise/amd64/cdh4-repository_1.0_all.deb
$ sudo dpkg -i cdh4-repository_1.0_all.deb

2. Add the Cloudera Public GPG Key to your repository

$ curl -s http://archive.cloudera.com/cdh4/ubuntu/precise/amd64/cdh/archive.key | sudo apt-key add

3. Install Hadoop with Yarn

$ sudo apt-get update
$ sudo apt-get install hadoop-conf-pseudo

Starting and verifying Hadoop is working correctly

For YARN, a pseudo-distributed Hadoop installation consists of one node running all five Hadoop daemons: namenode, secondarynamenode, resourcemanager, datanode, and nodemanager.

1. View files on the system

$ dpkg -L hadoop-conf-pseudo

2. Start the NameNode
Before starting the NameNode we must format the NameNode

$ sudo -u hdfs hdfs namenode -format

Start HDFS

$ for service in /etc/init.d/hadoop-hdfs-*; do $service start; done

To verify the services have started, we can check http://localhost:50070

3. Create /tmp directory and set permissions

$ sudo -u hdfs hadoop fs -mkdir /tmp
$ sudo -u hdfs hadoop fs -chmod -R 1777 /tmp

4. Create Staging and Log Directories
Create the staging directory and set permissions

$ sudo -u hdfs hadoop fs -mkdir /tmp/hadoop-yarn/staging
$ sudo -u hdfs hadoop fs -chmod -R 1777 /tmp/hadoop-yarn/staging

Create the done_intermediate directory under the staging directory and set permissions

$ sudo -u hdfs hadoop fs -mkdir /tmp/hadoop-yarn/staging/history/done_intermediate
$ sudo -u hdfs hadoop fs -chmod -R 1777 /tmp/hadoop-yarn/staging/history/done_intermediate

Change ownership on the staging directory and subdirectory

$ sudo -u hdfs hadoop fs -chown -R mapred:mapred /tmp/hadoop-yarn/staging

Create the /var/log/hadoop-yarn directory and set ownership

$ sudo -u hdfs hadoop fs -mkdir /var/log/hadoop-yarn
$ sudo -u hdfs hadoop fs -chown yarn:mapred /var/log/hadoop-yarn

5. Verify HDFS file structure

$ sudo -u hdfs hadoop fs -ls -R /

You should see the following directories

drwxrwxrwt   - hdfs   supergroup        0 2012-05-31 15:31 /tmp
drwxr-xr-x   - hdfs   supergroup        0 2012-05-31 15:31 /tmp/hadoop-yarn
drwxrwxrwt   - mapred mapred            0 2012-05-31 15:31 /tmp/hadoop-yarn/staging
drwxr-xr-x   - mapred mapred            0 2012-05-31 15:31 /tmp/hadoop-yarn/staging/history
drwxrwxrwt   - mapred mapred            0 2012-05-31 15:31 /tmp/hadoop-yarn/staging/history/done_intermediate
drwxr-xr-x   - hdfs   supergroup        0 2012-05-31 15:31 /var
drwxr-xr-x   - hdfs   supergroup        0 2012-05-31 15:31 /var/log
drwxr-xr-x   - yarn   mapred            0 2012-05-31 15:31 /var/log/hadoop-yarn

6. Start YARN

$ sudo service hadoop-yarn-resourcemanager start
$ sudo service hadoop-yarn-nodemanager start
$ sudo service hadoop-mapreduce-historyserver start

7. Create User Directories
Create a home directory for each MapReduce user. It is best to do this on the NameNode; for example:

$ sudo -u hdfs hadoop fs -mkdir  /user/
$ sudo -u hdfs hadoop fs -chown  /user/

where is the Linux username of each user.

Alternatively, you can log in as each Linux user and create the home directory as follows:

$ sudo -u hdfs hadoop fs -mkdir /user/$USER
$ sudo -u hdfs hadoop fs -chown $USER /user/$USER

Running an example application with YARN

Create a home directory on HDFS for the user who will be running the job (for example, duydo):

$ sudo -u hdfs hadoop fs -mkdir /user/duydo
$  sudo -u hdfs hadoop fs -chown duydo /user/duydo

Do the following steps as the user duydo.
Make a directory in HDFS called input and copy some XML files into it by running the following commands in pseudo-distributed mode:

$ hadoop fs -mkdir input
$ hadoop fs -put /etc/hadoop/conf/*.xml input
$ hadoop fs -ls input

Found 3 items:

-rw-r--r--   1 duydo supergroup       1348 2012-02-13 12:21 input/core-site.xml
-rw-r--r--   1 duydo supergroup       1913 2012-02-13 12:21 input/hdfs-site.xml
-rw-r--r--   1 duydo supergroup       1001 2012-02-13 12:21 input/mapred-site.xml

Set HADOOP_MAPRED_HOME for user duydo:

$ export HADOOP_MAPRED_HOME=/usr/lib/hadoop-mapreduce

Run an example Hadoop job to grep with a regular expression in our input data.

$ hadoop jar /usr/lib/hadoop-mapreduce/hadoop-mapreduce-examples.jar grep input output23 'dfs[a-z.]+'

After the job completes, we can find the output in the HDFS directory named output23 because we specified that output directory to Hadoop.

$ hadoop fs -ls
$ hadoop fs -ls output23

Found 2 items

drwxr-xr-x  -  duydo supergroup     0 2009-02-25 10:33   /user/duydo/output23/_SUCCESS
-rw-r--r--  1  duydo supergroup  1068 2009-02-25 10:33   /user/duydo/output23/part-r-00000

Read the results in the output file.

$ hadoop fs -cat output23/part-r-00000 | head
1    dfs.safemode.min.datanodes
1    dfs.safemode.extension
1    dfs.replication
1    dfs.permissions.enabled
1    dfs.namenode.name.dir
1    dfs.namenode.checkpoint.dir
1    dfs.datanode.data.dir

References:
https://ccp.cloudera.com/display/CDH4DOC/Installing+CDH4+on+a+Single+Linux+Node+in+Pseudo-distributed+Mode

You can download an example project at here and remember that only Spring version from 3.0.1 supports JPA 2 fully.

I. Add properties and dependencies into your POM.XML file

1. Add properties

<properties>
       ...
       <wicket.version>1.4.9</wicket.version>
       <spring.version>3.0.2.RELEASE</spring.version>
       <hibernate.version>3.5.1-Final</hibernate.version>
</properties>

2. Add Wicket dependencies

<!--  WICKET DEPENDENCIES -->
<dependency>
    <groupId>org.apache.wicket</groupId>
    <artifactId>wicket</artifactId>
    <version>${wicket.version}</version>
</dependency>
<dependency>
   <groupId>org.apache.wicket</groupId>
   <artifactId>wicket-extensions</artifactId>
   <version>${wicket.version}</version>
</dependency>

<!--  WICKET-SPRING DEPENDENCIES -->
 <dependency>
 <groupId>org.apache.wicket</groupId>
 <artifactId>wicket-spring</artifactId>
 <version>${wicket.version}</version>
 </dependency>

3. Add Spring 3 dependencies

<!--  SPRING DEPENDENCIES -->
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-core</artifactId>
 <version>${spring.version}</version>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-web</artifactId>
 <version>${spring.version}</version>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-beans</artifactId>
 <version>${spring.version}</version>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-aop</artifactId>
 <version>${spring.version}</version>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-context</artifactId>
 <version>${spring.version}</version>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-context-support</artifactId>
 <version>${spring.version}</version>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-tx</artifactId>
 <version>${spring.version}</version>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-jdbc</artifactId>
 <version>${spring.version}</version>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-orm</artifactId>
 <version>${spring.version}</version>
 </dependency>
 <dependency>
 <groupId>org.springframework</groupId>
 <artifactId>spring-test</artifactId>
 <version>${spring.version}</version>
 <scope>test</scope>
 </dependency>

4. Add JPA 2.o /Hibernate 3 dependencies

<!-- HIBERNATE 3.5.1 JPA -->
 <dependency>
 <groupId>org.hibernate.java-persistence</groupId>
 <artifactId>jpa-api</artifactId>
 <version>2.0-cr-1</version>
 </dependency>
 <dependency>
 <groupId>org.hibernate</groupId>
 <artifactId>hibernate-entitymanager</artifactId>
 <version>${hibernate.version}</version>
 </dependency>
<!-- C3p0 for Datasource -->
 <dependency>
 <groupId>c3p0</groupId>
 <artifactId>c3p0</artifactId>
 <version>0.9.0.4</version>
 </dependency>

<!-- H2 DEPENDENCIES for testing -->
 <dependency>
 <groupId>com.h2database</groupId>
 <artifactId>h2</artifactId>
 <version>1.2.125</version>
 </dependency>

II. Create applicationContext.xml for Spring 3
1. Create application.properties for datasource and jpa configuration:

# connection pool config (c3p0 ComboPooledDataSource)
# all time values are in seconds
c3p0.minPoolSize=2
c3p0.maxPoolSize=20
c3p0.maxConnectionAge=21600
c3p0.maxIdleTime=3600
c3p0.idleConnectionTestPeriod=300

# Development config with H2 database
jdbc.driver=org.h2.Driver
jdbc.url=jdbc:h2:~/your_database
jdbc.username=sa
jdbc.password=

jpa.databasePlatform=org.hibernate.dialect.HSQLDialect
jpa.generateDdl=true
jpa.showSql=true

2. An example applicatonContext.xml:

 <?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
 xmlns:tx="http://www.springframework.org/schema/tx" xmlns:p="http://www.springframework.org/schema/p"
 xmlns:aop="http://www.springframework.org/schema/aop"
 xsi:schemaLocation="http://www.springframework.org/schema/beans  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd  http://www.springframework.org/schema/context  http://www.springframework.org/schema/context/spring-context-3.0.xsd  http://www.springframework.org/schema/tx  http://www.springframework.org/schema/tx/spring-tx-3.0.xsd  http://www.springframework.org/schema/aop  http://www.springframework.org/schema/aop/spring-aop-3.0.xsd">

 <context:annotation-config />
 <context:component-scan base-package="com.duydo.model" />
 <tx:annotation-driven transaction-manager="transactionManager" />

 <context:property-placeholder location="classpath:application.properties"/>

 <bean id="dataSource">
 <property name="driverClass">
 <value>${jdbc.driver}</value>
 </property>
 <property name="jdbcUrl">
 <value>${jdbc.url}</value>
 </property>
 <property name="user">
 <value>${jdbc.username}</value>
 </property>
 <property name="password">
 <value>${jdbc.password}</value>
 </property>
 <property name="minPoolSize">
 <value>${c3p0.minPoolSize}</value>
 </property>
 <property name="maxPoolSize">
 <value>${c3p0.maxPoolSize}</value>
 </property>
 <property name="checkoutTimeout">
 <!-- Give up waiting for a connection after this many milliseconds -->
 <value>20000</value>
 </property>
 <property name="maxIdleTime">
 <value>${c3p0.maxIdleTime}</value>
 </property>
 <property name="idleConnectionTestPeriod">
 <value>${c3p0.idleConnectionTestPeriod}</value>
 </property>
 </bean>

 <bean
 class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" />

 <bean id="entityManagerFactory"
 class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
 <property name="persistenceUnitName" value="wsjhPU" />
 <property name="dataSource" ref="dataSource" />
 <property name="jpaVendorAdapter">
 <bean>
 <property name="databasePlatform" value="${jpa.databasePlatform}" />
 <property name="showSql" value="${jpa.showSql}" />
 <property name="generateDdl" value="${jpa.generateDdl}" />
 </bean>
 </property>
 </bean>
 <bean id="transactionManager">
 <property name="entityManagerFactory" ref="entityManagerFactory" />
 <property name="dataSource" ref="dataSource" />
 </bean>

 <bean id="wicketApplication" class="com.duydo.WicketApplication"/>

</beans>

III. Modify your PERSISTENCE.XML as following

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
 xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
 <persistence-unit name="wsjhPU" transaction-type="RESOURCE_LOCAL">
 <provider>org.hibernate.ejb.HibernatePersistence</provider>
 </persistence-unit>
</persistence>

IV. Modify your WEB.XML as following

<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
 version="2.4">

 <display-name>wicket-spring-jpa-hibernate</display-name>

 <context-param>
 <param-name>contextConfigLocation</param-name>
 <param-value>classpath:applicationContext.xml</param-value>
 </context-param>

 <filter>
 <filter-name>open.entitymanager.in.view</filter-name>
 <filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter</filter-class>
 </filter>

 <filter>
 <filter-name>wicket.wicket-spring-jpa-hibernate</filter-name>
 <filter-class>org.apache.wicket.protocol.http.WicketFilter</filter-class>
 <init-param>
 <param-name>applicationFactoryClassName</param-name>
 <param-value>org.apache.wicket.spring.SpringWebApplicationFactory</param-value>
 </init-param>
 <init-param>
 <param-name>configuration</param-name>
 <param-value>development</param-value>
 </init-param>
 </filter>

 <filter-mapping>
 <filter-name>open.entitymanager.in.view</filter-name>
 <url-pattern>/*</url-pattern>
 </filter-mapping>

 <filter-mapping>
 <filter-name>wicket.wicket-spring-jpa-hibernate</filter-name>
 <url-pattern>/*</url-pattern>
 </filter-mapping>

 <listener>
 <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
 </listener>
</web-app>

I will use Wordpress for example. We all know that every post in wordpress blog system has a status with possible values: draft, pending-review, published…

There are some ways to model the post entity. We can save status as an integer value in database: draft -> 0, pending-review -> 1, published -> 2

Version 1

@Entity
public class Post {
	private Integer status;

	public Integer getStatus() {
		return status;
	}

	public void setStatus(Integer status) {
		this.status = status;
	}
}

Well that’s ok. A client can use:

	Post post = ...;
	//Draft post
	post.setStatus(0);
	repository.store(post);

But this is not safe, the client can set any integer value for status. For more save, we can define constants for status values like that:

public class PostStatus {
	public static final Integer DRAFT = 0;
	public static final Integer PENDING_REVIEW = 1;
	public static final Integer PUBLISHED = 2;
}

The client can use:

	Post post = ...;
	//Draft post
	post.setStatus(PostStatus.DRAFT);
	repository.store(post);

But it is still not safe, because the client maybe do not use PostStatus class. So for more safe, what we need to do?
Yes, we can force the client use PostStatus by declaring PostStatus as an Enum and make it dependency in Post class:

Version 2

public enum PostStatus {
	DRAFT, PENDING_REVIEW, PUBLISHED;
}

@Entity
public class Post {
	@Enumerated
	private PostStatus status;

	public PostStatus getStatus() {
		return status;
	}

	public void setStatus(PostStatus status) {
		this.status = status;
	}
}

And now client can use it:

	Post post = ...;
	//Draft post
	post.setStatus(PostStatus.DRAFT);
	repository.store(post);

Well, it is better. But wait…
We know that JPA persists all enum constants in order we declare them in PostStatus with value started from 0. This is limitation, we can not change order of constants, we only can append a new constant. How does we solve this limitation?

Version 3

Enum type in Java 5 is wonderful, we can add constructor and do some business logic in it. Apply it we can re-write PostStatus like this:

public enum PostStatus {
	DRAFT(0),
	PENDING_REVIEW(1),
	PUBLISHED(2);

	private final Integer value;
	private PostStatus(Integer value) {
		this.value = value;
	}
	public Integer getValue() {
		return value;
	}
}

And Post class is re-wrote like this:

@Entity
public class Post {
	private Integer status;

	public PostStatus getStatus() {
		//TODO we need a helper to convert status value to PostStatus enum
		return ...;
	}

	public void setStatus(PostStatus status) {
		this.status = status.getValue();
	}
}

Great!!!

Now client can use code safety and we can add many constants as we want into PostStatus without worry about order of them.

It reminds me of the sentence the guy talked in Java4Ever trailer: “Look how beautiful, robust, secure, portable and scalable it is”

0. Install basic lib

sudo apt-get install build-essential libboost-dev automake libtool flex bison pkg-config

1. Get Thrift:

wget http://www.apache.org/dyn/closer.cgi?path=/incubator/thrift/0.2.0-incubating/thrift-0.2.0-incubating.tar.gz

2. Install Thrift

tar zxvf thrift-0.2.0-incubating.tar.gz
cd thrift-0.2.0-incubating
./bootstrap.sh
./configure --with-boost=/usr/local
make
sudo make install

3. Done

Làm quả screenshot cho vui nhà vui cửa

Trong quá trình đi minh ít khi nào dừng lại nghỉ, chủ yếu đi vệ sinh hoặc khát nước thì dừng lại. Cảm giác đi lên đèo thích lắm . Rất tiếc là lúc đó mình chưa có máy quay phim chứ không giờ có được thước phim ” Hành trình Quảng Ngãi – Sài Gòn bằng xe máy” cho ae thưởng ngoạn rồi hehe.

Ban đầu đi ai cũng không cho nhưng mình và bạn gái quyết định đi một chuyến cho biết cảm giác. Thật sự thì đi cũng không nguy hiểm như mọi người thường nghĩ. Kinh nghiệm của mình đi xe máy là phải luôn có kính chiếu hậu để quan sát dòng xe cộ phía sau, luôn cho xe chạy cách xe ô tô hoặc xe máy khác một khoảng cách an toàn, không bám đuôi hoặc cắt ngang đầu xe khác. Và khi đi phải nhìn xa xa để tránh mấy con chó hay chạy băng qua đường. Đang chạy tốc độ cao mà đụng mấy con này là coi như toi mạng. Chuyến đi này mình chỉ tốn 165.000 tiền xăng.

Tết này mình cũng chạy xe máy về Quảng Ngãi, anh em nào muốn thử cảm giác đi xe máy thì mình hẹn ngày lập hội đi cùng

When you run Page Speed, you get immediate suggestions on how you can change your web pages to improve their speed. For example, Page Speed automatically optimizes images for you, giving you a compressed image that you can use immediately on your web site. It also identifies issues such as JavaScript and CSS loaded by your page that wasn’t actually used to display the page, which can help reduce time your users spend waiting for the page to download and display.

You can download and install Page Speed at here

The idea of  “Fluent Interface” is instead of returning void in  setter methods of an object, returning an object to promote object chaining.

Example:

class Query {
    private String props;
    private String table;
    private String condition;

    public Query select(String props) {
        this.props = props;
        return this;
    }

    public Query from(String table) {
        this.table = table;
        return this;
    }

    public Query where(String condition) {
        this.condition = condition;
        return this;
    }

    public String buildQuery() {
        return String.format("SELECT %s FROM %s WHERE %s", props, table, condition);
    }
}

Instead of:

Query q = new Query();
q.select("username");
q.from("user");
q.where("username = 'duydo'");
String sql = q.buildQuery();

We can write:

Query q = new Query();
String sql = q.select(”username”).from(”user”).where(”username = ‘duydo’”).buildQuery();

This will make code more readable, but be careful when use this technique.