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Fix for owlike#123: Initial refactoring based on PR feedback
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30 changes: 30 additions & 0 deletions
30
genson/src/main/java/com/owlike/genson/reflect/Evolvable.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,30 @@ | ||
| package com.owlike.genson.reflect; | ||
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| import java.util.Map; | ||
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| /** | ||
| * An interface that can be implemented by data classes | ||
| * in order to support schema evolution. | ||
| * <p> | ||
| * This interface is used in combination with {@link EvolvableHandler} | ||
| * in order to prevent data loss during serialization across different | ||
| * versions of data classes. | ||
| * | ||
| * @author Aleksandar Seovic 2018.05.20 | ||
| */ | ||
| interface Evolvable { | ||
| /** | ||
| * Add unknown property to this instance. | ||
| * | ||
| * @param propName property name | ||
| * @param propValue property value | ||
| */ | ||
| void addUnknownProperty(String propName, Object propValue); | ||
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| /** | ||
| * Return a map of unknown properties. | ||
| * | ||
| * @return a map of unknown properties | ||
| */ | ||
| Map<String, Object> unknownProperties(); | ||
| } |
64 changes: 64 additions & 0 deletions
64
genson/src/main/java/com/owlike/genson/reflect/EvolvableHandler.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,64 @@ | ||
| package com.owlike.genson.reflect; | ||
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| import com.owlike.genson.Context; | ||
| import com.owlike.genson.GenericType; | ||
| import com.owlike.genson.stream.ObjectReader; | ||
| import com.owlike.genson.stream.ObjectWriter; | ||
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| import java.util.Map; | ||
| import java.util.function.Consumer; | ||
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| /** | ||
| * An implementation of an {@link UnknownPropertyHandler} that supports | ||
| * evolution of data classes via {@link Evolvable} interface. | ||
| * <p> | ||
| * If the target object we are deserializing into is {@link Evolvable}, | ||
| * this handler will add any unknown properties encountered during | ||
| * deserialization into {@link Evolvable#unknownProperties()} map, | ||
| * and will write them out along with all known properties during | ||
| * subsequent serialization. | ||
| * <p> | ||
| * This prevents data loss when serializing and deserializing the same | ||
| * JSON payload using different versions of Java data classes. | ||
| * | ||
| * @author Aleksandar Seovic 2018.05.20 | ||
| */ | ||
| public class EvolvableHandler implements UnknownPropertyHandler { | ||
| private static final GenericType<Object> UNKNOWN = new GenericType<Object>() {}; | ||
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| @Override | ||
| public <T> Consumer<T> onUnknownProperty(T target, String propName, ObjectReader reader, Context ctx) { | ||
| // TODO: change this to read property as an opaque value, using ObjectReader directly | ||
| Object propValue = ctx.genson.deserialize(UNKNOWN, reader, ctx); | ||
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| if (target == null) { | ||
| // this is a bit ugly... | ||
| // the issue is that we may not have a target object while parsing JSON when using creators, | ||
| // so we need to store the parsed value somewhere and apply it later | ||
| return objTarget -> { | ||
| if (objTarget instanceof Evolvable) { | ||
| ((Evolvable) objTarget).addUnknownProperty(propName, propValue); | ||
| } | ||
| }; | ||
| } | ||
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| if (target instanceof Evolvable) { | ||
| ((Evolvable) target).addUnknownProperty(propName, propValue); | ||
| } | ||
| return null; | ||
| } | ||
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| @Override | ||
| public <T> void writeUnknownProperties(T source, ObjectWriter writer, Context ctx) { | ||
| if (source instanceof Evolvable) { | ||
| Map<String, Object> props = ((Evolvable) source).unknownProperties(); | ||
| if (props != null) { | ||
| for (String propName : props.keySet()) { | ||
| writer.writeName(propName); | ||
| // TODO: change this to write property as an opaque value, using ObjectWriter directly | ||
| ctx.genson.serialize(props.get(propName), writer, ctx); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } |
29 changes: 29 additions & 0 deletions
29
genson/src/main/java/com/owlike/genson/reflect/EvolvableObject.java
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,29 @@ | ||
| package com.owlike.genson.reflect; | ||
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| import com.owlike.genson.annotation.JsonIgnore; | ||
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| import java.util.HashMap; | ||
| import java.util.Map; | ||
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| /** | ||
| * Convenience base class for {@link Evolvable} data classes. | ||
| * | ||
| * @author Aleksandar Seovic 2018.05.20 | ||
| */ | ||
| public abstract class EvolvableObject implements Evolvable { | ||
| @JsonIgnore | ||
| private Map<String, Object> unknownProperties; | ||
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| @Override | ||
| public void addUnknownProperty(String propName, Object propValue) { | ||
| if (unknownProperties == null) { | ||
| unknownProperties = new HashMap<>(); | ||
| } | ||
| unknownProperties.put(propName, propValue); | ||
| } | ||
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| @Override | ||
| public Map<String, Object> unknownProperties() { | ||
| return unknownProperties; | ||
| } | ||
| } |
56 changes: 56 additions & 0 deletions
56
genson/src/main/java/com/owlike/genson/reflect/UnknownPropertyHandler.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,56 @@ | ||
| package com.owlike.genson.reflect; | ||
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| import com.owlike.genson.Context; | ||
| import com.owlike.genson.stream.ObjectReader; | ||
| import com.owlike.genson.stream.ObjectWriter; | ||
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| import java.util.function.Consumer; | ||
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| /** | ||
| * An interface that defines callbacks that will be called when an | ||
| * unknown properties are encountered during deserialization, as well | ||
| * as to check if there are any unknown properties that should be | ||
| * written out during serialization. | ||
| * <p> | ||
| * The main purpose of this interface is to support schema evolution | ||
| * of objects that use JSON as a long term storage format, without | ||
| * loss of unknown properties across clients and severs using different | ||
| * versions of Java classes. | ||
| * | ||
| * @author Aleksandar Seovic 2018.05.09 | ||
| */ | ||
| public interface UnknownPropertyHandler { | ||
| /** | ||
| * Called whenever a property is encountered in a JSON document | ||
| * that doesn't have a corresponding {@link PropertyMutator}. | ||
| * <p> | ||
| * Typically, the implementation of this interface concerned | ||
| * with schema evolution will handle this event by storing | ||
| * property value somewhere so it can be written later by the | ||
| * {@link #writeUnknownProperties} method. | ||
| * | ||
| * @param target the object we are deserializing JSON into, if known | ||
| * @param propName the name of the unknown property | ||
| * @param reader the ObjectReader to read property value from | ||
| * @param ctx deserialization context | ||
| * | ||
| * @return the optional Consumer that will be called once the target object is known | ||
| */ | ||
| <T> Consumer<T> onUnknownProperty(T target, String propName, ObjectReader reader, Context ctx); | ||
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| /** | ||
| * Write unknown properties encountered during deserialization. | ||
| * <p> | ||
| * This method can be optionally implemented by {@code UnknownPropertyHandler}s | ||
| * that want to write unknown properties during serialization. The default | ||
| * implementation is a no-op. | ||
| * | ||
| * @param source the object we are serializing into JSON | ||
| * @param writer the ObjectReader to read property value from | ||
| * @param ctx serialization context | ||
| * | ||
| * @return a map of unknown properties | ||
| */ | ||
| default <T> void writeUnknownProperties(T source, ObjectWriter writer, Context ctx) { | ||
| } | ||
| } |
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