hydra.langs.json.JsonDecoding Maven / Gradle / Ivy
package hydra.langs.json;
import hydra.json.Value;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.function.Function;
import java.util.stream.Collectors;
/**
* Decoding functions for Hydra's native JSON values which are intended for use in Java.
* Decoding failures result in Java exceptions rather than failure flows.
*/
public abstract class JsonDecoding {
/**
* Decode a list from JSON.
*/
public static List decodeList(Function mapping, Value json) {
return json.accept(new Value.PartialVisitor>() {
@Override
public List otherwise(Value instance) {
throw unexpected("array", instance);
}
@Override
public List visit(Value.Array instance) {
return instance.value.stream().map(mapping).collect(Collectors.toList());
}
@Override
public List visit(Value.Null instance) {
return Collections.emptyList();
}
});
}
/**
* Decode a boolean value from JSON.
*/
public static boolean decodeBoolean(Value json) {
return json.accept(new Value.PartialVisitor() {
@Override
public Boolean otherwise(Value instance) {
throw unexpected("boolean", instance);
}
@Override
public Boolean visit(Value.Boolean_ instance) {
return instance.value;
}
});
}
/**
* Decode a double value from JSON.
*/
public static double decodeDouble(Value json) {
Number num = decodeNumber(json);
return num.doubleValue();
}
/**
* Decode a float value from JSON.
*/
public static float decodeFloat(Value json) {
Number num = decodeNumber(json);
return num.floatValue();
}
/**
* Decode an integer value from JSON.
*/
public static int decodeInteger(Value json) {
Number num = decodeNumber(json);
return num.intValue();
}
/**
* Decode a list field from JSON.
*/
public static List decodeListField(String name, Function mapping, Value json) {
// Note: this allows the field to be omitted, and also allows a null value, both resulting in an empty list
Optional> opt = decodeOptionalField(name, v -> decodeList(mapping, v), json, Collections.emptyList());
return opt.orElse(Collections.emptyList());
}
/**
* Decode a number from JSON.
*/
public static double decodeNumber(Value json) {
return json.accept(new Value.PartialVisitor() {
@Override
public Double otherwise(Value instance) {
throw unexpected("number", instance);
}
@Override
public Double visit(Value.Number_ instance) {
return instance.value;
}
});
}
/**
* Decode an object (key/value map) from JSON.
*/
public static Map decodeObject(Value json) {
return json.accept(new Value.PartialVisitor>() {
@Override
public Map otherwise(Value instance) {
throw unexpected("object", instance);
}
@Override
public Map visit(Value.Object_ instance) {
return instance.value;
}
});
}
/**
* Decode an optional double-valued field from JSON.
*/
public static Optional decodeOptionalDoubleField(String name, Value json) {
return decodeOptionalField(name, JsonDecoding::decodeDouble, json, null);
}
/**
* Decode an optional field from JSON.
*/
public static Optional decodeOptionalField(String name,
Function mapping,
Value json,
A defaultValue) {
Map map = decodeObject(json);
Value fieldValue = map.get(name);
if (fieldValue == null) {
return defaultValue == null ? Optional.empty() : Optional.of(defaultValue);
} else {
return fieldValue.accept(new Value.PartialVisitor>() {
@Override
public Optional otherwise(Value instance) {
return Optional.of(mapping.apply(fieldValue));
}
@Override
public Optional visit(Value.Null instance) {
return defaultValue == null ? Optional.empty() : Optional.of(defaultValue);
}
});
}
}
/**
* Decode an optional field from JSON.
*/
public static Optional decodeOptionalField(String name, Function mapping, Value json) {
return decodeOptionalField(name, mapping, json, null);
}
/**
* Decode an optional integer-valued field from JSON.
*/
public static Optional decodeOptionalIntegerField(String name, Value json) {
return decodeOptionalField(name, JsonDecoding::decodeInteger, json, null);
}
/**
* Decode an optional set-valued field from JSON.
*/
public static Optional> decodeOptionalSetField(String name, Function mapping, Value json) {
return decodeOptionalField(name, v -> decodeSet(mapping, v), json);
}
/**
* Decode a required field from JSON.
*/
public static A decodeRequiredField(String name, Function mapping, Value json, A defaultValue) {
Optional opt = decodeOptionalField(name, mapping, json);
if (opt.isPresent()) {
return opt.get();
} else {
throw new RuntimeException("missing required field \"" + name + "\"");
}
}
/**
* Decode a required field from JSON.
*/
public static A decodeRequiredField(String name, Function mapping, Value json) {
return decodeRequiredField(name, mapping, json, null);
}
/**
* Decode a required list-valued field from JSON.
*/
public static List decodeRequiredListField(String name, Function mapping, Value json) {
return decodeRequiredField(name, v -> decodeList(mapping, v), json, Collections.emptyList());
}
/**
* Decode a set from JSON.
*/
public static Set decodeSet(Function mapping, Value json) {
return new HashSet<>(decodeList(mapping, json));
}
/**
* Decode a string value from JSON.
*/
public static String decodeString(Value json) {
return json.accept(new Value.PartialVisitor() {
@Override
public String otherwise(Value instance) {
throw unexpected("string", instance);
}
@Override
public String visit(Value.String_ instance) {
return instance.value;
}
});
}
/**
* Decode a list of string values from JSON.
*/
public static List decodeStringList(Value json) {
return decodeList(JsonDecoding::decodeString, json);
}
/**
* Decode an enumerated value from JSON.
*/
public static A decodeEnum(Map values, Value json) {
String key = decodeString(json);
A value = values.get(key);
if (value == null) {
throw new RuntimeException("no such enum value: " + key);
} else {
return value;
}
}
/**
* Decode a union (injection) from JSON.
*/
public static A decodeUnion(Map> mappings, Value json) {
return json.accept(new Value.PartialVisitor() {
@Override
public A otherwise(Value instance) {
throw unexpected("string or object", instance);
}
@Override
public A visit(Value.Object_ instance) {
Map map = instance.value;
if (map.size() != 1) {
throw new RuntimeException("expected union, found object with " + map.size() + " fields");
}
Map.Entry entry = map.entrySet().iterator().next();
Function mapping = mappings.get(entry.getKey());
if (mapping == null) {
throw new RuntimeException("unexpected union value: " + entry.getKey());
} else {
return mapping.apply(entry.getValue());
}
}
@Override
public A visit(Value.String_ instance) {
Function mapping = mappings.get(instance.value);
if (mapping == null) {
throw new RuntimeException("unexpected union value: " + instance.value);
} else {
return mapping.apply(new Value.Null());
}
}
});
}
/**
* Fail on an unexpected JSON value.
*/
public static RuntimeException unexpected(String expected, Value actual) {
return new RuntimeException("expected " + expected + ", found " + actual);
}
}
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