package com.fasterxml.jackson.databind.node;

import java.io.IOException;

import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.jsontype.TypeSerializer;

This singleton node class is generated to denote "missing nodes" along paths that do not exist. For example, if a path via element of an array is requested for an element outside range of elements in the array; or for a non-array value, result will be reference to this node.

In most respects this placeholder node will act as NullNode; for example, for purposes of value conversions, value is considered to be null and represented as value zero when used for numeric conversions.

/** * This singleton node class is generated to denote "missing nodes" * along paths that do not exist. For example, if a path via * element of an array is requested for an element outside range * of elements in the array; or for a non-array value, result * will be reference to this node. *<p> * In most respects this placeholder node will act as {@link NullNode}; * for example, for purposes of value conversions, value is considered * to be null and represented as value zero when used for numeric * conversions. */
public final class MissingNode extends ValueNode { private static final long serialVersionUID = 1L; private final static MissingNode instance = new MissingNode();

NOTE: visibility raised to `protected` in 2.9.3 to allow custom subtypes (which may not be greatest idea ever to have but was requested)

/** *<p> * NOTE: visibility raised to `protected` in 2.9.3 to allow custom subtypes * (which may not be greatest idea ever to have but was requested) */
protected MissingNode() { } // To support JDK serialization, recovery of Singleton instance protected Object readResolve() { return instance; } @Override public boolean isMissingNode() { return true; } // Immutable: no need to copy @SuppressWarnings("unchecked") @Override public <T extends JsonNode> T deepCopy() { return (T) this; } public static MissingNode getInstance() { return instance; } @Override public JsonNodeType getNodeType() { return JsonNodeType.MISSING; } @Override public JsonToken asToken() { return JsonToken.NOT_AVAILABLE; } @Override public String asText() { return ""; } @Override public String asText(String defaultValue) { return defaultValue; } // // Note: not a numeric node, hence default 'asXxx()' are fine: /* public int asInt(int defaultValue); public long asLong(long defaultValue); public double asDouble(double defaultValue); public boolean asBoolean(boolean defaultValue); */ /* /********************************************************** /* Serialization: bit tricky as we don't really have a value /********************************************************** */ @Override public final void serialize(JsonGenerator g, SerializerProvider provider) throws IOException { /* Nothing to output... should we signal an error tho? * Chances are, this is an erroneous call. For now, let's * not do that; serialize as explicit null. Why? Because we * cannot just omit a value as JSON Object field name may have * been written out. */ g.writeNull(); } @Override public void serializeWithType(JsonGenerator g, SerializerProvider provider, TypeSerializer typeSer) throws IOException { g.writeNull(); } /* /********************************************************** /* Jackson 2.10 improvements for validation /********************************************************** */ @SuppressWarnings("unchecked") @Override public JsonNode require() { return _reportRequiredViolation("require() called on `MissingNode`"); } @SuppressWarnings("unchecked") @Override public JsonNode requireNonNull() { return _reportRequiredViolation("requireNonNull() called on `MissingNode`"); } @Override public int hashCode() { return JsonNodeType.MISSING.ordinal(); } /* /********************************************************** /* Standard method overrides /********************************************************** */ // 10-Dec-2019, tatu: Bit tricky case, see [databind#2566], but seems // best NOT to produce legit JSON. @Override public String toString() { return ""; } @Override public String toPrettyString() { return ""; } @Override public boolean equals(Object o) { /* Hmmh. Since there's just a singleton instance, this fails in all cases but with * identity comparison. However: if this placeholder value was to be considered * similar to SQL NULL, it shouldn't even equal itself? * That might cause problems when dealing with collections like Sets... * so for now, let's let identity comparison return true. */ return (o == this); } }