What is the best way to filter a Java Collection?

Question

I want to filter a java.util.Collection based on a predicate.

Answer 1

https://code.google.com/p/joquery/

Supports different possibilities,

Given collection,

Collection testList = new ArrayList<>();

of type,

class Dto
{
    private int id;
    private String text;

    public int getId()
    {
        return id;
    }

    public int getText()
    {
        return text;
    }
}

Filter

Java 7

Filter query = CQ.filter(testList)
    .where()
    .property("id").eq().value(1);
Collection filtered = query.list();

Java 8

Filter query = CQ.filter(testList)
    .where()
    .property(Dto::getId)
    .eq().value(1);
Collection filtered = query.list();

Also,

Filter query = CQ.filter()
        .from(testList)
        .where()
        .property(Dto::getId).between().value(1).value(2)
        .and()
        .property(Dto::grtText).in().value(new string[]{"a","b"});

Sorting (also available for the Java 7)

Filter query = CQ.filter(testList)
        .orderBy()
        .property(Dto::getId)
        .property(Dto::getName)
    Collection sorted = query.list();

Grouping (also available for the Java 7)

GroupQuery query = CQ.query(testList)
        .group()
        .groupBy(Dto::getId)
    Collection> grouped = query.list();

Joins (also available for the Java 7)

Given,

class LeftDto
{
    private int id;
    private String text;

    public int getId()
    {
        return id;
    }

    public int getText()
    {
        return text;
    }
}

class RightDto
{
    private int id;
    private int leftId;
    private String text;

    public int getId()
    {
        return id;
    }

    public int getLeftId()
        {
            return leftId;
        }

    public int getText()
    {
        return text;
    }
}

class JoinedDto
{
    private int leftId;
    private int rightId;
    private String text;

    public JoinedDto(int leftId,int rightId,String text)
    {
        this.leftId = leftId;
        this.rightId = rightId;
        this.text = text;
    }

    public int getLeftId()
    {
        return leftId;
    }

    public int getRightId()
        {
            return rightId;
        }

    public int getText()
    {
        return text;
    }
}

Collection leftList = new ArrayList<>();

Collection rightList = new ArrayList<>();

Can be Joined like,

Collection results = CQ.query().from(leftList)
                .innerJoin(CQ.query().from(rightList))
                .on(LeftFyo::getId, RightDto::getLeftId)
                .transformDirect(selection ->  new JoinedDto(selection.getLeft().getText()
                                                     , selection.getLeft().getId()
                                                     , selection.getRight().getId())
                                 )
                .list();

Expressions

Filter query = CQ.filter()
    .from(testList)
    .where()
    .exec(s -> s.getId() + 1).eq().value(2);