#About predicates

##Overview The purpose of predicates is obligate Griffin to check certain conditions before starting SparkSubmitJob. Depending on these conditions Griffin need to start or not start the measurement.

##Configure predicates

For configuring predicates need add property to measure json:

{
    ...
     "data.sources": [
        ...
         "connector": {
                   "predicates": [
                       {
                         "type": "file.exist",
                         "config": {
                           "root.path": "/path/to/",
                           "path": "file.ext,file2.txt"
                         }
                       }
                   ],
         ...
         }
}

Possible values for predicates.type:

• “file.exist” - in this case creates predicate with class org.apache.griffin.core.job.FileExistPredicator. This predicate checks existence of files before starting Spark jobs.

                    {
                        "type": "file.exist",
                        "config": {
                          "root.path": "/path/to/",
                          "path": "file.ext,file2.txt"
                        }
                      }

• “custom” - in this case required transmit class name in the property “class” in config. This example creates same predicate like in previous example

                     {
                         "type": "custom",
                         "config": {
                           "class": "org.apache.griffin.core.job.FileExistPredicator",
                           "root.path": "/path/to/",
                           "path": "file.ext,file2.txt"
                         }
                       }

It important to notice that predicate class must satisfy follow conditions:

• implement interface org.apache.griffin.core.job.Predicator
• have constructor with argument of type org.apache.griffin.core.job.entity.SegmentPredicate

##Deployment custom predicates For the creating custom predicate you need

1. Build the Griffin service using command As a result, two artifacts will be built

• service-VERSION.jar - executable Spring-Boot application
• service-VERSION-lib.jar - jar, which we can use as a dependency This step is necessary because we can't use executable Spring-Boot application as a dependency in our plugin.

2. Create module and add dependency that was built in previous step

         <dependency>
             <groupId>org.apache.griffin</groupId>
             <artifactId>service</artifactId>
             <classifier>lib</classifier>
             <version>${griffin.version}</version>
             <scope>provided</scope>
         </dependency>

3. Create a Predicate class, which should, as mentioned earlier, implement the Predicator interface and have a constructor with an argument of type SegmentPredicate
4. Build the module into a jar file and put it in any folder (for example /path-to-jar)
5. Start the Griffin service application using command

java -cp target/service-VERSION.jar -Dloader.path=/path-to-jar/ org.springframework.boot.loader.PropertiesLauncher