org.osgi.dto.DTO Maven / Gradle / Ivy
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/*
* Copyright (c) OSGi Alliance (2012, 2020). All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.osgi.dto;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* Super type for Data Transfer Objects.
*
* A Data Transfer Object (DTO) is easily serializable having only public fields
* of primitive types and their wrapper classes, String, enums, Version, and
* DTOs. List, Set, Map, and array aggregates may also be used. The aggregates
* must only hold objects of the listed types or aggregates. The types for Map
* keys are limited to primitive wrapper classes, String, enums, and Version.
*
* The object graph from a Data Transfer Object must be a tree to simplify
* serialization and deserialization.
*
* @author $Id: ffcb6416b152127a4c3fdca52426cacbe2f13a58 $
* @NotThreadSafe
*/
public abstract class DTO {
/**
* Return a string representation of this DTO suitable for use when
* debugging.
*
* The format of the string representation is not specified and subject to
* change.
*
* @return A string representation of this DTO suitable for use when
* debugging.
*/
@Override
public String toString() {
return appendValue(new StringBuilder(),
new IdentityHashMap(), "#", this).toString();
}
/**
* Append the specified DTO's string representation to the specified
* StringBuilder.
*
* @param result StringBuilder to which the string representation is
* appended.
* @param objectRefs References to "seen" objects.
* @param refpath The reference path of the specified DTO.
* @param dto The DTO whose string representation is to be appended.
* @return The specified StringBuilder.
*/
private static StringBuilder appendDTO(final StringBuilder result,
final Map objectRefs, final String refpath,
final DTO dto) {
result.append('{');
String delim = "";
for (Field field : dto.getClass().getFields()) {
if (Modifier.isStatic(field.getModifiers())) {
continue;
}
result.append(delim);
final String name = field.getName();
appendString(result, name);
result.append(':');
Object value = null;
try {
value = field.get(dto);
} catch (IllegalAccessException e) {
// use null value;
}
appendValue(result, objectRefs, refpath + "/" + name, value);
delim = ", ";
}
result.append('}');
return result;
}
/**
* Append the specified value's string representation to the specified
* StringBuilder.
*
* This method handles cycles in the object graph, using path-based
* references, even though the specification requires the object graph from
* a DTO to be a tree.
*
* @param result StringBuilder to which the string representation is
* appended.
* @param objectRefs References to "seen" objects.
* @param refpath The reference path of the specified value.
* @param value The object whose string representation is to be appended.
* @return The specified StringBuilder.
*/
private static StringBuilder appendValue(final StringBuilder result,
final Map objectRefs, final String refpath,
final Object value) {
if (value == null) {
return result.append("null");
}
// Simple Java types
if (value instanceof String || value instanceof Character) {
return appendString(result, compress(value.toString()));
}
if (value instanceof Number || value instanceof Boolean) {
return result.append(value.toString());
}
if (value instanceof Enum) {
return appendString(result, ((Enum< ? >) value).name());
}
if ("org.osgi.framework.Version".equals(value.getClass().getName())) {
return appendString(result, value.toString());
}
// Complex types
final String path = objectRefs.get(value);
if (path != null) {
result.append("{\"$ref\":");
appendString(result, path);
result.append('}');
return result;
}
objectRefs.put(value, refpath);
if (value instanceof DTO) {
return appendDTO(result, objectRefs, refpath, (DTO) value);
}
if (value instanceof Map) {
return appendMap(result, objectRefs, refpath, (Map< ? , ? >) value);
}
if (value instanceof List || value instanceof Set) {
return appendIterable(result, objectRefs, refpath,
(Iterable< ? >) value);
}
if (value.getClass().isArray()) {
return appendArray(result, objectRefs, refpath, value);
}
return appendString(result, compress(value.toString()));
}
/**
* Append the specified array's string representation to the specified
* StringBuilder.
*
* @param result StringBuilder to which the string representation is
* appended.
* @param objectRefs References to "seen" objects.
* @param refpath The reference path of the specified array.
* @param array The array whose string representation is to be appended.
* @return The specified StringBuilder.
*/
private static StringBuilder appendArray(final StringBuilder result,
final Map objectRefs, final String refpath,
final Object array) {
result.append('[');
final int length = Array.getLength(array);
for (int i = 0; i < length; i++) {
if (i > 0) {
result.append(',');
}
appendValue(result, objectRefs, refpath + "/" + i,
Array.get(array, i));
}
result.append(']');
return result;
}
/**
* Append the specified iterable's string representation to the specified
* StringBuilder.
*
* @param result StringBuilder to which the string representation is
* appended.
* @param objectRefs References to "seen" objects.
* @param refpath The reference path of the specified list.
* @param iterable The iterable whose string representation is to be
* appended.
* @return The specified StringBuilder.
*/
private static StringBuilder appendIterable(final StringBuilder result,
final Map objectRefs, final String refpath,
final Iterable< ? > iterable) {
result.append('[');
int i = 0;
for (Object item : iterable) {
if (i > 0) {
result.append(',');
}
appendValue(result, objectRefs, refpath + "/" + i, item);
i++;
}
result.append(']');
return result;
}
/**
* Append the specified map's string representation to the specified
* StringBuilder.
*
* @param result StringBuilder to which the string representation is
* appended.
* @param objectRefs References to "seen" objects.
* @param refpath The reference path of the specified map.
* @param map The map whose string representation is to be appended.
* @return The specified StringBuilder.
*/
private static StringBuilder appendMap(final StringBuilder result,
final Map objectRefs, final String refpath,
final Map< ? , ? > map) {
result.append('{');
String delim = "";
for (Map.Entry< ? , ? > entry : map.entrySet()) {
result.append(delim);
final String name = String.valueOf(entry.getKey());
appendString(result, name);
result.append(':');
final Object value = entry.getValue();
appendValue(result, objectRefs, refpath + "/" + name, value);
delim = ", ";
}
result.append('}');
return result;
}
/**
* Append the specified string to the specified StringBuilder.
*
* @param result StringBuilder to which the string is appended.
* @param string The string to be appended.
* @return The specified StringBuilder.
*/
private static StringBuilder appendString(final StringBuilder result,
final CharSequence string) {
result.append('"');
int i = result.length();
result.append(string);
while (i < result.length()) { // escape if necessary
char c = result.charAt(i);
if ((c == '"') || (c == '\\')) {
result.insert(i, '\\');
i = i + 2;
continue;
}
if (c < 0x20) {
result.insert(i + 1, Integer.toHexString(c | 0x10000));
result.replace(i, i + 2, "\\u");
i = i + 6;
continue;
}
i++;
}
result.append('"');
return result;
}
private static final int MAX_LENGTH = 100;
/**
* Compress, in length, the specified string.
*
* @param in The string to potentially compress.
* @return The string compressed, if necessary.
*/
private static CharSequence compress(final CharSequence in) {
final int length = in.length();
if (length <= MAX_LENGTH) {
return in;
}
StringBuilder result = new StringBuilder(MAX_LENGTH)
.append(in, 0, MAX_LENGTH / 2 - 3)
.append('.')
.append('.')
.append('.')
.append(in, length - (MAX_LENGTH / 2), length);
return result;
}
}