CODEWITHSUNDEEP
javacollectionsguava
rst
rst

Reputation: 15

how to do filter/query on in-memory list/map using guava

I have complex objects 

    class Person{
        Integer id;
        String fname;
        String lname;
        //..... there are more attributes
        List<Address> addresses;
    }
    class Address{
        String street1;
        String street2;
        String city;
        String state;
        String zip;
    }

I have about 30000 Person objects and each has at-least 200-500 sub object (addresses). Now I have all these in-memory and i have different scenarios (20-30 scenarios) where i have to query/filter objects based on filters available in scenarios. For eg.

In short, there are multiple scenarios with different combination of both the objects. Please advice the best way to utilize Guava for such case?

Upvotes: 2

Views: 1732

Answers (1)

Olivier Gr&#233;goire
Olivier Gr&#233;goire

Reputation: 35467

You should use Iterables.filter(Iterable, Predicate) in conjuction with Predicates.

Example:

public class PersonLastNameEqualsPredicate implements Predicate<Person> {
  private String personName;
  public PersonNameEqualsPredicate (String personName) {this.personName= personName;}
  public boolean apply(Person p) { return this.personName.equals(p.getLName()); }
}

public class PersonStreet1EqualsPredicate implements Predicate<Person> {
  private String street1Name;
  public PersonStreet1EqualsPredicate (String street1Name) {this.street1Name = street1Name;}
  public boolean apply(Person p) {
    for (Address a: p.getAddresses()) {
      if (street1Name.equals(a.getStreet1()) return true;
    }
    return false;
  }
}

// Extra predicates as you need them

You need one predicate per scenario item. Then you need to modulate them as you need them:

1.

Predicate<Person> peopleNamedZoik = new PersonLastNamePredicate("zoik");

2.

Predicate<Person> peopleNamedSmarkAndLivingInXyzStreet = Predicates.and(new PersonLastNamePredicate("smark"), new PersonStreet1EqualsPredicate("xyz"));

3.

Here you should adapt your street predicate to check at once if all street names contain all your expectation.

Then it's simply a matter of

1.

List<Person> myLongPersonList = ...;
Iterable<Person> zoikPeople = Iterables.filter(myLongPersonList, peopleNamedZoik);

2.

List<Person> myLongPersonList = ...;
Iterable<Person> zoikPeople = Iterables.filter(myLongPersonList, peopleNamedSmarkAndLivingInXyzStreet);

And so on.

Upvotes: 3

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