Install Docker in Ubuntu 17.10 Manually

Downaload DEB file.

Visit URL: https://download.docker.com/linux/ubuntu/dists/

Select Ubuntu 17.10 repo name artful
Execute following command to repo name

lsb_release -cs

Select stable or edge as preference

Select binary file of amd64, armhf or s390x based on the computer processor

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Spring JPA – Saving list items in entity

Spring JPA provides easy way to saving entity in database than traditional SQL operation. Here, developer can populate entity object and trigger save function in relevant repository. In entity population, developer must be aware on list operation.

Scenario:

@Entity
@Table(name="hotelinfo")
public class HotelInfoEntity {

 @Id
 @GeneratedValue(strategy=GenerationType.IDENTITY)
 private Long id;
 
 private String name;
 
 private String address;
 
 @ManyToOne(fetch=FetchType.LAZY)
 @JoinColumn(name = "countryid")
 private CountryEntity country;
 
 @OneToMany(mappedBy = "hotelInfo", cascade = CascadeType.ALL, orphanRemoval=true)
 private List rooms = new ArrayList<>();

 public List getRooms() {
  return rooms;
 }

 public void setRooms(List rooms) {
  this.rooms = rooms;
 }

 ... getter and setter methods of rest 
}

Incorrect implementation:

Most of developer do mistake when set list parameters ( Eg: setRooms(List rooms) ). They create the array and call to setter function to set list attribute to object.

It is wrong. It could cause to following error, specially in update operation.

Error:

This object keeps the reference to room list. When developer crates new array and assigned using setter method, reference to room list in hotel entity might be lost. Hence following error could happen.

2017-11-08 10:38:37.557 ERROR 3756 --- [nio-8080-exec-7] r.r.h.p.setup.service.PromotionService : IN SAVE 
org.springframework.orm.jpa.JpaSystemException: A collection with cascade="all-delete-orphan" was no longer referenced by the owning entity instance: com.example.samplespringboot.entity.RoomEntity; nested exception is org.hibernate.HibernateException: A collection with cascade="all-delete-orphan" was no longer referenced by the owning entity instance: com.example.samplespringboot.entity.RoomEntity
 at org.springframework.orm.jpa.vendor.HibernateJpaDialect.convertHibernateAccessException(HibernateJpaDialect.java:333)
 at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:244)
 at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:521)
 at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:761)

Solution:

To add list items

Stop creating new array and assigned to list directly.
Do add element to list.
Eg:

hotelInfoEnt.getRooms().add(e);

To clear list

Clear list
Eg:

hotelInfoEnt.getRooms().clear();

Java 8 – Lambda – List Operatoins

Java 8 feature, Lambda, provides features to process List easily.

Model class:

public class User {
 private Long id;
 private String firstName;
 private String lastName;
 private int age;
 private String city;
 private LocalDate dateOfBirth;

 // Getter and setter methods
}

List to Map

Key: id of user object
Value: user obeject

Option 1

Map<Long, User> userIdMap = userList.stream().collect(Collectors.toMap(User::getId, x -> x));

Option 2

Map<Long, User> userIdMap = userList.stream().collect(Collectors.toMap(x -> x.getId(), x -> x));

List to Map (Object parameters)

Key: id of user object
Value: first name of user object

Option 1

Map<Long, String> userIdMap = userList.stream().collect(Collectors.toMap(x -> x.getId(), x -> x.getFirstName()));

Option 2

Map<Long, String> userIdMap = userList.stream().collect(Collectors.toMap(User::getId, User::getFirstName));

Key: id of user object
Value: name concatenating first and and last names

Map<Long, String> userFullNameMap = userList.stream().collect(Collectors.toMap(x -> x.getId(), x -> (x.getFirstName() + " " + x.getLastName()) ));

Filter

Filter user object by age

 List<User> result = userList.stream()
                          .filter(x -> x.getAge() > 29)
                          .collect(Collectors.toList());

Filtered output as List

 List<User> result = userList.stream()
                          .filter(x -> x.getAge() > 29)
                          .collect(Collectors.toCollection(ArrayList::new));

Filtered output as Set

 Set<User> result = userList.stream()
                          .filter(x -> x.getAge() > 29)
                          .collect(Collectors.toCollection(HashSet::new));

 

 

Jcloud NoSuchMethodError in Rackspace Cloud File implementation

Rackspace cloud file feature was implemented with out project. In the deployment, it gave the no such method. error as following.

java.util.ServiceConfigurationError: org.jclouds.providers.ProviderMetadata: Provider org.jclouds.rackspace.cloudfiles.uk.CloudFilesUKProviderMetadata could not be instantiated: java.lang.NoSuchMethodError: com.google.common.base.Objects.firstNonNull(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
 at java.util.ServiceLoader.fail(ServiceLoader.java:207)
 at java.util.ServiceLoader.access$100(ServiceLoader.java:164)
 at java.util.ServiceLoader$LazyIterator.next(ServiceLoader.java:353)

Then I went through all the required libraries and configuration but could not find any missing items. Then I searched on Internet but given suggestion are not helpful. Finally, the decision was to check every libraries in deployment environment which causes to conflicted.

Affected libraries:
checkstyle-5.4-all.jar
compiler.jar

After struggling with all libraries on entire project in many hours, two libraries were found affecting to be conflicted. We removed those jar files since they are no longer required for deployment. Then cloud file feature works successfully.

Then we found out how these libraries affected to be conflicted. These libraries has used class files which were available in google-collect.jar. Later it was renamed with guava and it is developed. Rackspace cloud files uses guava-17.0.jar. It works properly with Rackspace cloud files integration.

Database Transaction not worked in MySQL

I work on java project. It accesses MySQL database and is deployed in Jboss 7. I need to implement the database transaction inside the project. Event though I modified java code, it was not worked. I looked into Jboss 7 changes, related to database transaction and could not find the any changes.

Then I developed a sample java project that accesses the MySQL database. It is deployed in Jboss 7. Database was created, using XAMPP. By default, it set InnoDB as database engine. It worked properly. Whilst testing on that project, I changed the database engine to MyISAM. Here, I could notice, database transaction did not work.

With that perception, I searched on database engines in MySQL. It gives the better conclusion. MySQL uses two major database engines. Those are InnoDB and MyISAM. They have considerable major changes. One of them is based on database transaction. InnoDB supports transaction and MyISAM does not.

Again, I back to the real project. Its database used two types of engines. Initial database is built with InnoDB. Later, one of team member of made some changes for few tables. Those engine has been set MyISAM. Therefore, the real project does not perform the database transactions. These modifications has been made on the  earlier version of MySQL. Therefore it set the MyISAM for engine.

By default, the newer version of MySQL sets InnoDB as the database engine. Earlier versions sets MyISAM database.

වියපත් තොටියා

නුඹෙ තාම යෞවනය
යයි මා හා සිනා සලා
මා මෙතන වියපත්ව
හිදිමි ඔබ දෙසම බලා

මවා දිය රැලි පෙලි
මතකයේ මවාලා
වාරු වූ අතැගිලි
හබලටම ගෙවීලා

මා ගත ද වැහැරි
ඔරු කදත් දිරාලා
අදුර ගලද්දී
උලලේනා හඩාලා

Transaction Error in Jboss 5.1

I wanted to deploy a web project on Jboss 5.1, which was deployed in Jboss 4.0 successfully. I could deploy the project in Jboss 5.1 properly but it gives following user transaction error whilst executing.


12:06:47,640 ERROR [STDERR] java.lang.ClassCastException: org.jboss.tm.usertx.cl
ient.ServerVMClientUserTransaction cannot be cast to javax.transaction.UserTrans
action

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