Json.java

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package com.sun.faces.util;

import static com.sun.faces.util.Json.Option.SKIP_NULL_VALUES;
import static com.sun.faces.util.Json.Option.USE_RFC1123_DATE;
import static java.time.ZoneOffset.UTC;
import static java.time.format.DateTimeFormatter.ISO_INSTANT;
import static java.time.format.DateTimeFormatter.RFC_1123_DATE_TIME;
import static java.util.Arrays.asList;
import static java.util.EnumSet.copyOf;
import static java.util.EnumSet.noneOf;

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.io.StringWriter;
import java.io.Writer;
import java.lang.reflect.Array;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.time.Instant;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Collection;
import java.util.Date;
import java.util.EnumSet;
import java.util.Map;
import java.util.Map.Entry;

import javax.json.stream.JsonGenerator;

/**
 * <p>
 * Generic JSON encoder using javax.json API.
 * <p>
 * This supports the standard types {@link Boolean}, {@link Number}, {@link Character}, {@link CharSequence},
 * {@link Date}, {@link LocalDate} and {@link Instant}.
 * If the given object type does not match any of them, then it will attempt to inspect the object as a JavaBean
 * using the {@link Introspector}, whereby the public properties (public getters) will be encoded as a JS object.
 * It also supports arrays, {@link Collection}s and {@link Map}s of them, even nested ones.
 * The dates are formatted as ISO8601 instant via {@link DateTimeFormatter#ISO_INSTANT}, so you can if necessary
 * just pass the value straight to <code>new Date(value)</code> in JavaScript.
 * <p>
 * Below encoding options are available:
 * <li>{@link Option#SKIP_NULL_VALUES}: skip null values in arrays, collections, maps and beans.
 * This may reduce an unnecessarily bloated JSON object.
 * <li>{@link Option#USE_RFC1123_DATE}: format dates as RFC1123 via {@link DateTimeFormatter#RFC_1123_DATE_TIME}.
 * This may improve compatibility with older web browsers.
 *
 * @author Bauke Scholtz
 * @since 2.3
 */
public class Json {

    private static final String ERROR_INVALID_BEAN = "Cannot introspect object of type '%s' as bean.";
    private static final String ERROR_INVALID_GETTER = "Cannot invoke getter of property '%s' of bean '%s'.";

    public enum Option {

        /**
         * Skip null values in arrays, collections, maps and beans.
         * This may reduce an unnecessarily bloated JSON object.
         */
        SKIP_NULL_VALUES,

        /**
         * Format dates as RFC1123 via {@link DateTimeFormatter#RFC_1123_DATE_TIME}.
         * This may improve compatibility with older web browsers.
         */
        USE_RFC1123_DATE;

    }

    /**
     * Encodes the given object as JSON and returns a string in JSON format.
     * The encoded object will be available as <code>data</code> property of the JS object in the returned JSON string.
     *
     * @param object The object to be encoded as JSON.
     * @param options The encoding options.
     * @return The JSON-encoded representation of the given object.
     * @throws IllegalArgumentException When given object or one of its properties cannot be inspected as a JavaBean.
     */
    public static String encode(Object object, Option... options) {
        StringWriter writer = new StringWriter();
        encode(object, writer, options);
        return writer.toString();
    }

    /**
     * Encodes the given object as JSON while streaming the string in JSON format to the given writer.
     * The encoded object will be available as <code>data</code> property of the JS object in the returned JSON string.
     *
     * @param object The object to be encoded as JSON.
     * @param writer The writer to stream the encoded output to.
     * @param options The encoding options.
     * @throws IllegalArgumentException When given object or one of its properties cannot be inspected as a JavaBean.
     */
    public static void encode(Object object, Writer writer, Option... options) {
        try (JsonGenerator generator = javax.json.Json.createGenerator(writer)) {
            generator.writeStartObject();
            encode("data", object, generator, options.length == 0 ? noneOf(Option.class) : copyOf(asList(options)));
            generator.writeEnd();
        }
    }

    private static void encode(String name, Object object, JsonGenerator generator, EnumSet<Option> options) {
        if (object == null) {
            encodeNull(name, generator);
        }
        else if (object instanceof Boolean) {
            encodeBoolean(name, (Boolean) object, generator);
        }
        else if (object instanceof BigDecimal) {
            encodeBigDecimal(name, (BigDecimal) object, generator);
        }
        else if (object instanceof Double) {
            encodeDouble(name, (Double) object, generator);
        }
        else if (object instanceof BigInteger) {
            encodeBigInteger(name, (BigInteger) object, generator);
        }
        else if (object instanceof Integer) {
            encodeInteger(name, (Integer) object, generator);
        }
        else if (object instanceof Number) {
            encodeLong(name, ((Number) object).longValue(), generator);
        }
        else if (object instanceof Character) {
            encodeString(name, ((Character) object).toString(), generator);
        }
        else if (object instanceof CharSequence) {
            encodeString(name, ((CharSequence) object).toString(), generator);
        }
        else if (object instanceof Date) {
            encodeInstant(name, ((Date) object).toInstant().atZone(UTC).toInstant(), generator, options);
        }
        else if (object instanceof LocalDate) {
            encodeInstant(name, ((LocalDate) object).atStartOfDay(UTC).toInstant(), generator, options);
        }
        else if (object instanceof Instant) {
            encodeInstant(name, (Instant) object, generator, options);
        }
        else if (object.getClass().isArray()) {
            encodeArray(name, object, generator, options);
        }
        else if (object instanceof Collection<?>) {
            encodeCollection(name, (Collection<?>) object, generator, options);
        }
        else if (object instanceof Map<?, ?>) {
            encodeMap(name, (Map<?, ?>) object, generator, options);
        }
        else {
            encodeBean(name, object, generator, options);
        }
    }

    private static void encodeNull(String name, JsonGenerator generator) {
        if (name == null) {
            generator.writeNull();
        }
        else {
            generator.writeNull(name);
        }
    }

    private static void encodeBoolean(String name, Boolean value, JsonGenerator generator) {
        if (name == null) {
            generator.write(value);
        }
        else {
            generator.write(name, value);
        }
    }

    private static void encodeBigDecimal(String name, BigDecimal value, JsonGenerator generator) {
        if (name == null) {
            generator.write(value);
        }
        else {
            generator.write(name, value);
        }
    }

    private static void encodeDouble(String name, double value, JsonGenerator generator) {
        if (name == null) {
            generator.write(value);
        }
        else {
            generator.write(name, value);
        }
    }

    private static void encodeBigInteger(String name, BigInteger value, JsonGenerator generator) {
        if (name == null) {
            generator.write(value);
        }
        else {
            generator.write(name, value);
        }
    }

    private static void encodeInteger(String name, int value, JsonGenerator generator) {
        if (name == null) {
            generator.write(value);
        }
        else {
            generator.write(name, value);
        }
    }

    private static void encodeLong(String name, long value, JsonGenerator generator) {
        if (name == null) {
            generator.write(value);
        }
        else {
            generator.write(name, value);
        }
    }

    private static void encodeString(String name, String value, JsonGenerator generator) {
        if (name == null) {
            generator.write(value);
        }
        else {
            generator.write(name, value);
        }
    }

    private static void encodeInstant(String name, Instant value, JsonGenerator generator, EnumSet<Option> options) {
        encodeString(name, (options.contains(USE_RFC1123_DATE) ? RFC_1123_DATE_TIME : ISO_INSTANT).format(value), generator);
    }

    private static void encodeArray(String name, Object array, JsonGenerator generator, EnumSet<Option> options) {
        if (name == null) {
            generator.writeStartArray();
        }
        else {
            generator.writeStartArray(name);
        }

        boolean skipNullValues = options.contains(SKIP_NULL_VALUES);

        for (int i = 0; i < Array.getLength(array); i++) {
            Object value = Array.get(array, i);

            if (!(value == null && skipNullValues)) {
                encode(null, value, generator, options);
            }
        }

        generator.writeEnd();
    }

    private static void encodeCollection(String name, Collection<?> collection, JsonGenerator generator, EnumSet<Option> options) {
        if (name == null) {
            generator.writeStartArray();
        }
        else {
            generator.writeStartArray(name);
        }

        boolean skipNullValues = options.contains(SKIP_NULL_VALUES);

        for (Object value : collection) {
            if (!(value == null && skipNullValues)) {
                encode(null, value, generator, options);
            }
        }

        generator.writeEnd();
    }

    private static void encodeMap(String name, Map<?, ?> map, JsonGenerator generator, EnumSet<Option> options) {
        if (name == null) {
            generator.writeStartObject();
        }
        else {
            generator.writeStartObject(name);
        }

        boolean skipNullValues = options.contains(SKIP_NULL_VALUES);

        for (Entry<?, ?> entry : map.entrySet()) {
            Object value = entry.getValue();

            if (!(value == null && skipNullValues)) {
                encode(String.valueOf(entry.getKey()), value, generator, options);
            }
        }

        generator.writeEnd();
    }

    private static void encodeBean(String name, Object bean, JsonGenerator generator, EnumSet<Option> options) {
        BeanInfo beanInfo;

        try {
            beanInfo = Introspector.getBeanInfo(bean.getClass());
        }
        catch (IntrospectionException e) {
            throw new IllegalArgumentException(String.format(ERROR_INVALID_BEAN, bean.getClass()), e);
        }

        if (name == null) {
            generator.writeStartObject();
        }
        else {
            generator.writeStartObject(name);
        }

        boolean skipNullValues = options.contains(SKIP_NULL_VALUES);

        for (PropertyDescriptor property : beanInfo.getPropertyDescriptors()) {
            if (property.getReadMethod() == null || "class".equals(property.getName())) {
                continue;
            }

            Object value;

            try {
                value = property.getReadMethod().invoke(bean);
            }
            catch (Exception e) {
                throw new IllegalArgumentException(String.format(ERROR_INVALID_GETTER, property.getName(), bean.getClass()), e);
            }

            if (!(value == null && skipNullValues)) {
                encode(property.getName(), value, generator, options);
            }
        }

        generator.writeEnd();
    }

}