Create Finder method for Service builder in liferay

For example, If I want to fetch all the students who are in standard 8, there is no direct method available. At max, we can call getStudents method (Which will return all students), and then from the list, we can take the 8th standard student programmatically. But this is not an efficient way. In the case of let say, 10000 students, if the total no of 8th standard student is just 30, then there is no meaning to fetch all 10000 students.

Liferay provides a finder method technique to achieve this. Let us see how to write the finder method.

So far now, we have created the student entity as per the below snippet(I am omitting the DTD definition).

<entity name="Student" local-service="true" remote-service="false">
  <column name="studentId" type="long" primary="true" />
  <column name="name" type="String" />
  <column name="age" type="int" />
  <column name="fatherName" type="String" />
  <column name="motherName" type="String" />
  <column name="standard" type="int" />
 </entity>

Add finder method

We are going to add the finder method to this entity. Generally, finder methods are built on columns so first we need to identify on which column(s) we want finder methods. 

I would recommend looking at the index page ‘A Complete Liferay Guide‘ to browse all topics about Liferay.

In our case, we want to search for all the students who are from the 8th Standard. So we will write the finder method on column standard. We will add the finder element for standard column so that finally it will look like the below snippet.

<entity name="Student" local-service="true" remote-service="false">
  <column name="studentId" type="long" primary="true" />
  <column name="name" type="String" />
  <column name="age" type="int" />
  <column name="fatherName" type="String" />
  <column name="motherName" type="String" />
  <column name="standard" type="int" />
  
  <finder return-type="Collection" name="Standard">
   <finder-column name="standard"/>
  </finder>
 </entity>

Explanation:-

• We have defined one element (finder) inside student entity. This will create finder method for column standard.
• The value of return-type is Collection which means that the return type of finder method will be List<T>.
• The value of name attribute will be used to construct finder method name. We gave Standard so the generated finder method name will be findByStandard().
  • Note:- You can give any value in name attribute of <finder> element. The only thing you need to make sure it to give first letter as capital. It will still work if you give first letter small. But then the method name become findBystandard() which should be findByStandard() (Camel Case as Java coding standard).
• <finder-column> element Inside the <finder> element represents the column name.
• the name attribute of <finder-column> element represents the name of the column. It should have the exact same name as <column>’s name attribute of which we want finder method.

Now run the service builder by ant build-service command and refresh the page. After running it, the finder method won’t be directly created inside StudentLocalServiceUtil class. The finder method will be created inside 

• StudentPersistence.java (under /WEB-INF/service/com/opensource/techblog/myservice/service/persistence/)
• StudentPersistenceImpl.java (under WEB-INF/src/com/opensource/techblog/myservice/service/persistence).

/**
  * 
  * @param standard
  * @return List<Student>
  * @throws SystemException
  */
 public List<Student> getStudentForStandard(int standard) throws SystemException{
  return this.studentPersistence.findByStandard(standard);
 }

Explanation:-

• We first declare method (getStudentForStandard) which takes standard as input and return the list of the students who are for a specific standard.
• The name of the method can be taken as anything that you feel relevant since it’s our custom method. The same signature method will be created in StudentLocalServiceUtil  class on the next service build. The method inside the StudentLocalServiceUtil will call the corresponding method of StudentLocalServiceImpl  class.
• Next we are calling this.studentPersistence.findByStandard method.
• This is because StudentLocalServiceImpl method extends StudentLocalServiceBaseImpl class and this (StudentLocalSeriveBaseImpl) class having reference of persistence (StudentPersistence) class.
• After the first service run the finder method is created in the persistence (StudentPersistence) class which is accessible now in StudentLocalServiceImpl class.
• So we are simply calling the finder method from the persistence class and pass the standard which gives the list of students for that particular standard which finally we return of this method (getStudentForStandard).
• Next, just run the service builder once again and refresh the project structure. This time you will observe that the corresponding method (with the same signature as what we defined in StudentLocalServiceImpl class) is created for StudentLocalServiceUtil class as per the below screenshot.

• Finder methods are the way to define customization in the service layer provided by Liferay
• It allows adding additional methods to fetch data from the database
• We can get data from one or more DB columns with a specific value.