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Create GenericMappingDemo.java
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‎GenericMappingDemo.java‎

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public class GenericMappingDemo {
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static class A {
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private Integer integerA;
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private String stringA;
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private Float floatA;
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public A(final Integer integerA, final String stringA, final Float floatA) {
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this.integerA = integerA;
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this.stringA = stringA;
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this.floatA = floatA;
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}
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public Integer getIntegerA() {
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return integerA;
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}
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public void setIntegerA(final Integer integerA) {
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this.integerA = integerA;
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}
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public String getStringA() {
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return stringA;
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}
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public void setStringA(final String stringA) {
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this.stringA = stringA;
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}
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public Float getFloatA() {
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return floatA;
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}
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public void setFloatA(final Float floatA) {
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this.floatA = floatA;
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}
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@Override
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public String toString() {
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return "A{integerA=" + integerA + ", stringA='" + stringA + "', floatA=" + floatA + '}';
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}
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}
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static class B {
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private Integer integerB;
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private String stringB;
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public Integer getIntegerB() {
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return integerB;
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}
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public void setIntegerB(final Integer integerB) {
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this.integerB = integerB;
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}
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public String getStringB() {
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return stringB;
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}
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public void setStringB(final String stringB) {
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this.stringB = stringB;
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}
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@Override
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public String toString() {
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return "B{integerB=" + integerB + ", stringB='" + stringB + '\'' + '}';
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}
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}
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static class C {
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private Float floatC;
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private String stringC;
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public Float getFloatC() {
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return floatC;
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}
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public void setFloatC(final Float floatC) {
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this.floatC = floatC;
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}
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public String getStringC() {
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return stringC;
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}
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public void setStringC(final String stringC) {
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this.stringC = stringC;
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}
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@Override
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public String toString() {
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return "C{floatC=" + floatC + ", stringC='" + stringC + "'}";
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}
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}
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static class GenericMapping<C, T> {
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final int id;
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final Class<C> type;
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final Function<C, T> getter;
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final BiConsumer<C, T> setter;
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public GenericMapping(final int id,
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final Class<C> type,
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final Function<C, T> getter,
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final BiConsumer<C, T> setter) {
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this.id = id;
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this.type = type;
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this.getter = getter;
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this.setter = setter;
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}
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}
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static class Mapper {
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// All mappings by class and id
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private final Map<Class<?>, Map<Integer, GenericMapping<?, ?>>> mappings
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= new HashMap<>();
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public void addMapping(GenericMapping<?, ?> mapping) {
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mappings.computeIfAbsent(mapping.type,
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c -> new TreeMap<>()).put(mapping.id, mapping);
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}
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/**
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* Map values from one object to another,
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* using any mapping ids that apply to both classes
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* @param from The object to transfer values from
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* @param to The object to transfer values to
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*/
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public <From, To> void map(From from, To to) {
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Map<Integer, GenericMapping<?, ?>> getters
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= mappings.get(from.getClass());
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Map<Integer, GenericMapping<?, ?>> setters
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= mappings.get(to.getClass());
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if (getters == null || setters == null) {
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// Nothing to do
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return;
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}
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// Create a set with the ids in both getters and
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// setters, i.e. the mappings that apply
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Set<Integer> ids = new HashSet<>(getters.keySet());
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ids.retainAll(setters.keySet());
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// Transfer all mappings
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for (Integer id : ids) {
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GenericMapping<From, ?> getter
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= (GenericMapping<From, ?>) getters.get(id);
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GenericMapping<To, ?> setter
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= (GenericMapping<To, ?>) setters.get(id);
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transfer(from, to, getter, setter);
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}
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}
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private <From, To, V> void transfer(final From from,
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final To to, final GenericMapping<From, ?> getter,
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final GenericMapping<To, V> setter) {
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// This will throw an exception if the mappings are invalid
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final V value = (V) getter.getter.apply(from);
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setter.setter.accept(to, value);
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}
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}
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public static void main(String[] args) {
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final Mapper mapper = new Mapper();
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// Mapping definition for class A
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mapper.addMapping(new GenericMapping<>(1, A.class,
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A::getIntegerA, A::setIntegerA));
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mapper.addMapping(new GenericMapping<>(2, A.class,
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A::getStringA, A::setStringA));
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mapper.addMapping(new GenericMapping<>(3, A.class,
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A::getFloatA, A::setFloatA));
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// Mapping definition for class B
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mapper.addMapping(new GenericMapping<>(1, B.class,
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B::getIntegerB, B::setIntegerB));
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mapper.addMapping(new GenericMapping<>(2, B.class,
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B::getStringB, B::setStringB));
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// Mapping definition for class C
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mapper.addMapping(new GenericMapping<>(2, C.class,
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C::getStringC, C::setStringC));
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mapper.addMapping(new GenericMapping<>(3, C.class,
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C::getFloatC, C::setFloatC));
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// Use the mappings
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A a = new A(7, "foo", 3.7f);
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B b = new B();
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C c = new C();
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System.out.printf("A before map: %s%n", a);
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System.out.printf("B before map: %s%n", b);
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System.out.printf("C before map: %s%n", c);
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// This will transfer a.integerA to b.integerB and a.stringA to b.stringB
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mapper.map(a, b);
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// This will transfer a.stringA to c.stringC and a.floatA to c.floatC
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mapper.map(a, c);
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System.out.println();
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System.out.printf("A after map: %s%n", a);
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System.out.printf("B after map: %s%n", b);
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System.out.printf("C after map: %s%n", c);
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}
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}

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