My use case was to write a generic CSV transformer, which should be able to convert any Java POJO to CSV string.
My Implementation :
public <T> List<String> convertToString(List<T> objectList) {
List<String> stringList = new ArrayList<>();
char delimiter = ',';
char quote = '"';
String lineSep = "\n";
CsvMapper mapper = new CsvMapper();
CsvSchema schema = mapper.schemaFor(!HOW_TO!);
for (T object : objectList) {
try {
String csv = mapper.writer(schema
.withColumnSeparator(delimiter)
.withQuoteChar(quote)
.withLineSeparator(lineSep)).writeValueAsString(object);
} catch (JsonProcessingException e) {
System.out.println(e);
}
}
return stringList;
}
I was using Jackson-dataformat-csv library, but I'm stuck with !HOW_TO! part, ie How to extract the .class of the object from the objectList. I was studying and came across Type Erasure, So I think it is somehow not possible other than giving the .class as parameter to my function. But I'm also extracting this object list from generic entity using Java Reflection, so I can't have the option to provide the .class params.
Is there a workaround for this?
OR
Any other approaches/libraries where I can convert a generic List<T> objectList to List<String> csvList
with functionality of adding delimiters, quote characters, line separators etc.
Thanks!
I have created a CSVUtil Class similar to below which uses java reflection.
Example to use below CSVUtil Assuming POJO Student ,
List<Student> StudentList = new ArrayList<Student>();
String StudentCSV = CSVUtil.toCSV(StudentList,' ',false);
import java.lang.reflect.Field;
import java.util.List;
import java.util.logging.Logger;
CSVUtil class
public class CSVUtil {
private static final Logger LOGGER = Logger.getLogger(CSVUtil.class .getName());
private final static char DEFAULT_SEPARATOR = ' ';
public static String toCSV(List<?> objectList, char separator, boolean displayHeader) {
StringBuilder result =new StringBuilder();
if (objectList.size() == 0) {
return result.toString();
}
if(displayHeader){
result.append(getHeaders(objectList.get(0),separator));
result.append("\n");
}
for (Object obj : objectList) {
result.append(addObjectRow(obj, separator)).append("\n");
}
return result.toString();
}
public static String getHeaders(Object obj,char separator) {
StringBuilder resultHeader = new StringBuilder();
boolean firstField = true;
Field fields[] = obj.getClass().getDeclaredFields();
for (Field field : fields) {
field.setAccessible(true);
String value;
try {
value = field.getName();
if(firstField){
resultHeader.append(value);
firstField = false;
}
else{
resultHeader.append(separator).append(value);
}
field.setAccessible(false);
} catch (IllegalArgumentException e) {
LOGGER.severe(e.toString());
}
}
return resultHeader.toString();
}
public static String addObjectRow(Object obj, char separator) {
StringBuilder csvRow =new StringBuilder();
Field fields[] = obj.getClass().getDeclaredFields();
boolean firstField = true;
for (Field field : fields) {
field.setAccessible(true);
Object value;
try {
value = field.get(obj);
if(value == null)
value = "";
if(firstField){
csvRow.append(value);
firstField = false;
}
else{
csvRow.append(separator).append(value);
}
field.setAccessible(false);
} catch (IllegalArgumentException | IllegalAccessException e) {
LOGGER.severe(e.toString());
}
}
return csvRow.toString();
}
}