Spring Data Repo Interface

    //PersonRepository.java

    package com.pockettheories;

    import org.springframework.data.mongodb.repository.Aggregation;
    import org.springframework.data.mongodb.repository.MongoRepository;
    import org.springframework.data.mongodb.repository.Query;
    import org.springframework.data.repository.query.Param;
    import org.springframework.stereotype.Repository;
    import java.util.List;

    @Repository
    public interface PersonRepository extends MongoRepository<Person, String> { //the 2nd generic is data type of ID
    List<Person> findPersonsByFirstName(String firstName);

    @Query("{'firstName': :#{#fname}}")
    List<Person> findPersonByDisplayName(@Param("fname") String displayName);

    @Query("{'firstName': ?0}")
    List<Person> findPersonByDisplayName2(String displayName);

    @Aggregation(pipeline = {
        "{'$match':  {'firstName':  ?0}}",
        "{'$sort':  {'firstName':  1}}"
    })
    List<Person> findPersonByGoodName(String name);
    }

    //PersonService.java

    package com.pockettheories;

    import org.springframework.stereotype.Service;
    import org.springframework.beans.factory.annotation.Autowired;

    import java.util.List;

    @Service
    public class PersonService {
    @Autowired
    public PersonRepository repository;

    public List<Person> findPersonsByFirstName(String firstName) {
        return repository.findPersonsByFirstName(firstName);
    }

    public List<Person> findPersonsByFirstName2(String firstName) {
        return repository.findPersonByDisplayName(firstName);
    }

    public List<Person> findPersonsByFirstName3(String firstName) {
        return repository.findPersonByGoodName(firstName);
    }

    public void insert(Person p) {
        repository.insert(p);
    }

    public List<Person> getAll() {
        return repository.findAll();
    }
    }

    //PersonController.java

    package com.pockettheories;

    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.http.ResponseEntity;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.PathVariable;
    import org.springframework.web.bind.annotation.RestController;

    import java.util.List;

    @RestController
    public class PersonController {
    @Autowired
    protected PersonService service;

    @GetMapping("/")
    public String index() {
        return "Hello World!";
    }

    @GetMapping("/name/{name}")
    public String getByName(@PathVariable String name) {
        List<Person> lstPerson = service.findPersonsByFirstName(name);
        String retVal = "";
        if (lstPerson.size()==0) {
        retVal = "No results";
        } else {
        retVal = lstPerson.get(0).toString();
        }
        return retVal;
    }

    @GetMapping("/name2/{name}")
    public String getByName2(@PathVariable String name) {
        List<Person> lstPerson = service.findPersonsByFirstName2(name);
        String retVal = "";
        if (lstPerson.size()==0) {
        retVal = "No results";
        } else {
        retVal = lstPerson.get(0).toString();
        }
        return retVal;
    }

    @GetMapping("/name3/{name}")
    public String getByName3(@PathVariable String name) {
        List<Person> lstPerson = service.findPersonsByFirstName3(name);
        String retVal = "";
        if (lstPerson.size()==0) {
        retVal = "No results";
        } else {
        retVal = lstPerson.get(0).toString();
        }
        return retVal;
    }

    @GetMapping("/save/{name}")
    public String saveName(@PathVariable String name) {
        String firstName = name.split(" ")[0];
        String lastName = name.split(" ")[1];

        Person p = new Person();
        p.id = String.format("%s %s", firstName, lastName);
        p.firstName = firstName;
        p.lastName = lastName;

        service.insert(p);

        return "OK";
    }

    public ResponseEntity getAll() {
        return ResponseEntity.ok(service.getAll());
    }
    }


    //Person.java

    package com.pockettheories;

    public class Person {
    public String id;
    public String firstName;
    public String lastName;

    public String toString() {
        StringBuilder strBuild = new StringBuilder();
        strBuild.append(String.format("id: %s\n", id));
        strBuild.append(String.format("firstName: %s\n", firstName));
        strBuild.append(String.format("lastName: %s\n", lastName));
        return strBuild.toString();
    }
    }