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anonymous /GsonPrettyPrinter.java
Created Oct 22, 2009

package com.github;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.Map.Entry;
import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
/**
* A decent pretty-printer for Gson. Features include:
*
* <ul>
* <li>Will try to use a single line where possible</li>
* <li>Configurable indent string</li>
* </ul>
*
* This file is (c) Copyright 2009 Uprizer Labs LLC It is released to the public under the Lesser GNU Public License
* v3.0 See http://www.gnu.org/licenses/lgpl.html for details.
*
* @author Ian Clarke <ian@uprizer.com>, minor additions by Eric Poggel (NuOrbit Media, nuorbit.com)
* @see http://gist.github.com/212791, http://blog.locut.us/main/2009/10/18/a-good-pretty-printer-for-google-gson.html
*
* @example
* new GsonPrettyPrinter(gb.create()).ppJson(some_object);
*/
public class GsonPrettyPrinter {
private static <V> SortedSet<Entry<String, V>> orderEntrySet(final Set<Entry<String, V>> es) {
final TreeSet<Entry<String, V>> ret = new TreeSet<Entry<String, V>>(new Comparator<Entry<String, V>>() {
public int compare(final Entry<String, V> o1, final Entry<String, V> o2) {
return o1.getKey().compareTo(o2.getKey());
}
});
ret.addAll(es);
return ret;
}
private final Gson gson;
private static final int MAX_LEN_FOR_ONE_LINE = 150;
private final String indent;
public GsonPrettyPrinter(final Gson gson) {
this(gson, " ");
}
public GsonPrettyPrinter(final Gson gson, final String indent) {
this.gson = gson;
this.indent = indent;
}
public String ppJson(final Object o) {
return ppJson(o, null);
}
public String ppJson(final Object o, Type t) {
if (t==null)
t = o.getClass();
final StringWriter sw = new StringWriter();
final PrintWriter pw = new PrintWriter(sw);
ppJson(o, pw, t);
return sw.toString();
}
public void ppJson(final Object o, final PrintWriter pw, Type t) {
final JsonElement jsonTree = gson.toJsonTree(o, t);
final List<String> stringList = toStringList(jsonTree);
for (final String s : stringList) {
pw.println(s);
}
}
private List<String> arrayToStringList(final JsonArray jsonArray) {
final List<List<String>> sll = new LinkedList<List<String>>();
for (final JsonElement arrayElement : jsonArray) {
sll.add(toStringList(arrayElement));
}
// Can we fit the array on a single line?
boolean oneLine = true;
int approxLineLength = 0;
for (final List<String> sl : sll) {
if (sl.size() > 1) {
oneLine = false;
break;
}
approxLineLength += sl.get(0).length() + 2;
}
if (approxLineLength > MAX_LEN_FOR_ONE_LINE) {
oneLine = false;
}
if (oneLine) {
final StringBuffer sb = new StringBuffer(approxLineLength * 2 + 10);
sb.append("[");
boolean first = true;
for (final List<String> sl : sll) {
if (!first) {
sb.append(", ");
}
first = false;
sb.append(sl.get(0));
}
sb.append("]");
return Collections.singletonList(sb.toString());
}
final LinkedList<String> ret = new LinkedList<String>();
ret.add("[");
int oPos = 0;
for (final List<String> sl : sll) {
oPos++;
final int slLen = sl.size();
int pos = 0;
for (final String s : sl) {
pos++;
final boolean needComma = (pos == slLen && oPos < sll.size());
ret.add(indent + s + (needComma ? ", " : ""));
}
}
ret.add("]");
return ret;
}
private List<String> objectToStringList(final JsonObject jsonObject) {
final Map<String, List<String>> slm = new HashMap<String, List<String>>();
for (final Entry<String, JsonElement> e : jsonObject.entrySet()) {
slm.put(e.getKey(), toStringList(e.getValue()));
}
// Can we fit the object on a single line?
boolean oneLine = true;
int approxLineLength = 0;
for (final Entry<String, List<String>> e : slm.entrySet()) {
if (e.getValue().size() > 1) {
oneLine = false;
break;
}
approxLineLength += e.getKey().length() + e.getValue().get(0).length() + 6;
}
if (approxLineLength > MAX_LEN_FOR_ONE_LINE) {
oneLine = false;
}
if (oneLine) {
final StringBuffer sb = new StringBuffer(approxLineLength * 2 + 10);
sb.append("{");
boolean first = true;
for (final Entry<String, List<String>> e : orderEntrySet(slm.entrySet())) {
if (!first) {
sb.append(", ");
}
first = false;
sb.append("\"" + e.getKey() + "\" : " + e.getValue().get(0));
}
sb.append("}");
return Collections.singletonList(sb.toString());
}
final LinkedList<String> ret = new LinkedList<String>();
ret.add("{");
int oPos = 0;
for (final Entry<String, List<String>> e : orderEntrySet(slm.entrySet())) {
oPos++;
final int slLen = e.getValue().size();
int pos = 0;
for (final String s : e.getValue()) {
pos++;
final boolean needComma = (pos == slLen && oPos < slm.size());
if (pos == 1) {
ret.add(indent + "\"" + e.getKey() + "\" : " + s + (needComma ? ", " : ""));
} else {
ret.add(indent + s + (needComma ? ", " : ""));
}
}
}
ret.add("}");
return ret;
}
private List<String> toStringList(final JsonElement je) {
if (je==null || je.isJsonNull())
return new ArrayList<String>(Arrays.asList(new String[]{"null"}));
if (je.isJsonPrimitive())
return Collections.singletonList(je.getAsJsonPrimitive().toString());
if (je.isJsonArray()) {
final JsonArray jsonArray = je.getAsJsonArray();
return arrayToStringList(jsonArray);
} else if (je.isJsonObject()) {
final JsonObject jsonObject = je.getAsJsonObject();
return objectToStringList(jsonObject);
}
throw new RuntimeException("Unsupported Json element: " + je.getClass().getName());
}
}
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