将HashMap写入Csv文件

Question

I have a hashmap with a String key and List(String) as values.

For Example:

Key | Values
John | GroupName1,GroupName2,GroupName3
Nick | Groupname4,GroupName1

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

John,GroupName1,GroupName2,GroupName3    
Nick,Groupname4,GroupName1

I tried:

Map<String, List<String>> usersmap = (Map<String, List<String>>) model.get("users"); //this is my map
StringWriter output = new StringWriter();
ICsvListWriter listWriter;
listWriter = new CsvListWriter(output, CsvPreference.STANDARD_PREFERENCE);
for (Map.Entry<String, List<String>> entry : usersmap.entrySet()) {
    listWriter.write(entry.getKey(), entry.getValue());
}

but it doesn't seem right to me.

Answer 1

Try to convert your List into a comma separated string using String.join(...)

listWriter.write(entry.getKey(), String.join(",", entry.getValue());

Java documentation:

https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#join-java.lang.CharSequence-java.lang.Iterable-