Wednesday, May 9, 2012

Converting Java Map to String

Java Collections framework, String manipulation etc is something that we often encounter in Development process.
For processing collections (like checking null/empty, Intersection, Disjunction) We do have some of the very use full libraries.

Some of the Collection related libraries are Apche Commons Collections and Google  Collections(Guava).

Problem Use Case

This article explains how to convert a Java Map to String(and vice versa) using different libraries and technique.

One way is to use StringBuilder(Or String) and loop though the Map and build the String by applying some sort of separator ( for key:value and entry). Here we have to take care of the null value etc.

Without Any Library
If we want to convert the map to a String with key value separator and also individual entry seperator in the resulting String, we have to write code for that. For a simple Map, we have to iterate though the map, take care of the null values etc. Following is a sample to get String built out from Map Contents

public static String getStringFromMapOrdinary(Map map,String ENTRY_SEPERATOR, String MAP_KEYVALUE_SEPERATOR ) {
     StringBuilder stringBuilder = new StringBuilder();
     for (String key : map.keySet()) {
      if (stringBuilder.length() > 0) {
      String value = map.get(key);
      try {
       stringBuilder.append((key != null ? URLEncoder.encode(key, "UTF-8") : ""));
       stringBuilder.append(value != null ? URLEncoder.encode(value, "UTF-8") : "");
      } catch (UnsupportedEncodingException e) {
       throw new RuntimeException("Exception Occured", e);
     return stringBuilder.toString();

Apache Commons

Something similar is already provided by Apache Common StringUtils.join() method.

Which will return something like,
Returns = blogTitle:Sidd blogDate:today blogContent:Sidd's First Blog

Google Guava
The Guava project contains several of Google's core libraries that we rely on in our Java-based projects: collections, caching, primitives support etc.

The same thing can be done nicely using the Google Guava which provides some interesting methods.
Instead of the above method which has to take care of the null values, iteration etc, we can use Google oiner as follows,
return Joiner.on(" ").withKeyValueSeparator(":").join(myContentMap);

The full source code with other example hands on with Guava would be posted soon.


  1. map.toString() will retur same way

  2. map.toString will call the toString method of the java.util.AbstractMap which might not return a very useful String.