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root-talis/InheritanceTypeIdResolver.java

Created September 8, 2017 09:06
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  1. root-talis created this gist Sep 8, 2017.
    124 changes: 124 additions & 0 deletions InheritanceTypeIdResolver.java
    View file
    Original file line number Diff line number Diff line change
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    /*
    * Automatic inheritance type resolver for Jackson.
    * @author root_talis<https://github.com/root-talis>
    *
    *
    * Usage:
    *
    * @JsonTypeInfo(use = JsonTypeInfo.Id.CUSTOM, include = JsonTypeInfo.As.PROPERTY, property = "discriminator")
    * @JsonTypeIdResolver(InheritanceTypeIdResolver.class)
    * class Animal { // can be abstract or interface
    * // ...
    * }
    *
    * // no additional annotations needed to parse json into this class
    * class Cat extends Animal {
    * // ...
    * }
    *
    * // no additional annotations needed to parse json into this class
    * class Lion extends Cat {
    * // ...
    * }
    *
    * // no additional annotations needed to parse json into this class
    * class Dog extends Animal {
    * // ...
    * }
    *
    *
    * Maven dependency:
    *
    * <dependency>
    * <groupId>org.reflections</groupId>
    * <artifactId>reflections</artifactId>
    * <version>0.9.9-RC1</version>
    * </dependency>
    */

    package my.package.utils;

    import com.fasterxml.jackson.annotation.JsonTypeInfo;
    import com.fasterxml.jackson.databind.DatabindContext;
    import com.fasterxml.jackson.databind.JavaType;
    import com.fasterxml.jackson.databind.jsontype.TypeIdResolver;
    import com.fasterxml.jackson.databind.type.TypeFactory;
    import org.reflections.Reflections;

    import java.io.IOException;
    import java.lang.reflect.Modifier;
    import java.util.HashMap;
    import java.util.Map;
    import java.util.Set;


    public class InheritanceTypeIdResolver implements TypeIdResolver {
    private JavaType baseType;
    private Map<String, JavaType> typeMap = new HashMap<>();

    @Override
    public void init(JavaType javaType) {
    baseType = javaType;

    Class<?> clazz = baseType.getRawClass();

    Reflections reflections = new Reflections("my.package"); // root package to scan for subclasses
    Set<Class<?>> subtypes = (Set<Class<?>>)reflections.getSubTypesOf(clazz);

    int classModifiers = clazz.getModifiers();

    if (!Modifier.isAbstract(classModifiers) && !Modifier.isInterface(classModifiers)) {
    subtypes.add(clazz);
    }

    subtypes.forEach(type -> {
    String key = type.getSimpleName();

    if (typeMap.containsKey(key)) {
    throw new IllegalStateException("Type name \"" + key + "\" already exists.");
    }

    typeMap.put(type.getSimpleName(), TypeFactory.defaultInstance().constructSpecializedType(baseType, type));
    });
    }

    @Override
    public String idFromValue(Object o) {
    return idFromValueAndType(o, o.getClass());
    }

    @Override
    public String idFromBaseType() {
    return idFromValueAndType(null, baseType.getRawClass());
    }

    @Override
    public String idFromValueAndType(Object o, Class<?> aClass) {
    String name = aClass.getSimpleName();

    if (typeMap.containsKey(name)) {
    return typeMap.get(name).getRawClass().getSimpleName();
    }

    return null;
    }

    @Override
    public JavaType typeFromId(DatabindContext databindContext, String s) throws IOException {
    if (typeMap.containsKey(s)) {
    return typeMap.get(s);
    }

    throw new IOException("Cannot find class for type id \"" + s + "\"");
    }

    @Override
    public String getDescForKnownTypeIds() {
    return null;
    }

    @Override
    public JsonTypeInfo.Id getMechanism() {
    return JsonTypeInfo.Id.CUSTOM;
    }
    }