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Java - Write hashmap to a csv file

I have a hashmap with a String key and String value. It contains a large number of keys and their respective values.

For example:

key | value
abc | aabbcc
def | ddeeff

I would like to write this hashmap to a csv file such that my csv file contains rows as below:


I tried the following example here using the supercsv library: http://javafascination.blogspot.com/2009/07/csv-write-using-java.html. However, in this example, you have to create a hashmap for each row that you want to add to your csv file. I have a large number of key value pairs which means that several hashmaps, with each containing data for one row need to be created. I would like to know if there is a more optimized approach that can be used for this use case.

like image 949
activelearner Avatar asked Jul 01 '15 21:07


3 Answers

Something like this should do the trick:

String eol = System.getProperty("line.separator");

try (Writer writer = new FileWriter("somefile.csv")) {
  for (Map.Entry<String, String> entry : myHashMap.entrySet()) {
} catch (IOException ex) {
like image 147
Sean Bright Avatar answered Nov 01 '22 08:11

Sean Bright

Using the Jackson API, Map or List of Map could be written in CSV file. See complete example here

 * @param listOfMap
 * @param writer
 * @throws IOException
public static void csvWriter(List<HashMap<String, String>> listOfMap, Writer writer) throws IOException {
    CsvSchema schema = null;
    CsvSchema.Builder schemaBuilder = CsvSchema.builder();
    if (listOfMap != null && !listOfMap.isEmpty()) {
        for (String col : listOfMap.get(0).keySet()) {
        schema = schemaBuilder.build().withLineSeparator(System.lineSeparator()).withHeader();
    CsvMapper mapper = new CsvMapper();
like image 12
Ajay Kumar Avatar answered Nov 01 '22 09:11

Ajay Kumar

As your question is asking how to do this using Super CSV, I thought I'd chime in (as a maintainer of the project).

I initially thought you could just iterate over the map's entry set using CsvBeanWriter and a name mapping array of "key", "value", but this doesn't work because HashMap's internal implementation doesn't allow reflection to get the key/value.

So your only option is to use CsvListWriter as follows. At least this way you don't have to worry about escaping CSV (every other example here just joins with commas...aaarrggh!):

public void writeHashMapToCsv() throws Exception {
    Map<String, String> map = new HashMap<>();
    map.put("abc", "aabbcc");
    map.put("def", "ddeeff");

    StringWriter output = new StringWriter();
    try (ICsvListWriter listWriter = new CsvListWriter(output, 
        for (Map.Entry<String, String> entry : map.entrySet()){
            listWriter.write(entry.getKey(), entry.getValue());



like image 4
James Bassett Avatar answered Nov 01 '22 10:11

James Bassett