JarCastingBremersee Comparator
This project contains a builder for comparing and sorting objects.
The comparator can compare any kind of objects which have the same attributes or the same 'getters'. It uses reflection to get the values of these attributes or 'getters'. The values may be a simple type like java.lang.String or a complex type which implements java.lang.Comparable.
Maven Site
Usage
Given is for example a tree that is represented by these classes:
The common Node class:
import java.util.Date;
abstract class Node {
private Date createdAt;
private String name;
// getter and setter
}
The Branch class:
import java.util.List;
import java.util.ArrayList;
class Branch extends Node {
private List<Node> children = new ArrayList<>();
// getter
}
The Leaf class:
class Leaf extends Node {
private String value;
// getter and setter
}
You want to sort a list of nodes by name. And if the names are equal by created date:
import org.bremersee.comparator.*;
import java.util.List;
import java.util.ArrayList;
class Example {
public static void main(String[] args) {
List<Node> list = new ArrayList<>();
// add nodes
list.sort(ComparatorBuilder.builder()
.add("name", true, true, false) // fieldName, asc, ignoreCase, nullIsFirst
.add("createdAt", false, true, false) // fieldName, asc, ignoreCase, nullIsFirst
.build());
}
}
That's all. All nodes in the list are sorted by name and date. But what happens, if you want to sort them by type (first the branches and then the leafs) and then by name and date? There is no field that stores the type. Then you can do this:
import org.bremersee.comparator.*;
import java.util.List;
import java.util.ArrayList;
class Example {
public static void main(String[] args) {
List<Node> list = new ArrayList<>();
// add nodes
list.sort(ComparatorBuilder.builder()
.add((o1, o2) ->
(o1 instanceof Branch && o2 instanceof Branch) ? 0 : o1 instanceof Branch ? -1 : 1)
.add("name", true, true, false) // fieldName, asc, ignoreCase, nullIsFirst
.add("createdAt", false, true, false) // fieldName, asc, ignoreCase, nullIsFirst
.build());
}
}
Now you have a list, that contains the branches first, sorted by name and date, and then the leafs.
The definition of the sorting can also be described by a string. The string of the example above can look like this:
type|name|createdAt,desc
The syntax is:
fieldName0,asc,ignoreCase,nullIsFirst|fieldName1,desc,ignoreCase,nullIsFirst
The pipe (|) character separtes the fields. The field values are separated by comma (,). The defaults are asc = true, ignoreCase = true and nullIsFirst = false and can be omitted. That's why
type|name|createdAt,desc
is a short form for
type,asc,true,false|name,asc,true,false|createdAt,asc,true,false
The field name can also be a path to a value, if you have complex objects:
room.number,asc,true,false|person.lastName,asc,true,false|person.firstName,asc,true,false
if your class looks like this for example:
class Employee {
private Person person;
private Room room;
// getter and setter
}
with Person
class Person {
private String lastName;
private String firstName;
// getter and setter
}
and Room
class Room {
private int number;
// getter and setter
}
Let's sort our list of nodes with this 'well known text':
import org.bremersee.comparator.*;
import java.util.Comparator;
import java.util.List;
import java.util.ArrayList;
class Example {
public static void main(String[] args) {
List<Node> list = new ArrayList<>();
// add nodes
list.sort(ComparatorBuilder.builder()
.fromWellKnownText("type|name|createdAt,desc", comparatorField -> {
if ("type".equals(comparatorField.getField())) {
return (Comparator) (o1, o2) -> (o1 instanceof Branch && o2 instanceof Branch)
? 0
: o1 instanceof Branch ? -1 : 1;
}
return new ValueComparator(comparatorField);
})
.build());
}
}
XML Schema
The XML schema of the model is available here.
Spring Framework Support
The Spring Common Data project contains a class for sorting, too. The class ComparatorSpringUtils contains methods to transform the comparator fields of this library into the objects of the spring framework.
To use the Spring Framework Support you have to add the following dependency to your project:
<dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-commons</artifactId>
<version>{your-spring-data-commons-version}</version>
</dependency>