package de.aikiit.fotocollector.main;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;

import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * @author hirsch
 * @version 2016-03-10, 23:38
 */
public class DateJacksonSerializer extends JsonSerializer<Date> {
    @Override
    public void serialize(final Date value, final JsonGenerator gen, final SerializerProvider serializers) throws IOException, JsonProcessingException {
        String formattedDate = value != null ? new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(value) : "none";
        gen.writeString(formattedDate);
    }
}

package de.aikiit.fotocollector.main;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;

import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

/**
 * @author hirsch
 * @version 2016-03-10, 23:38
 */
public class DateJacksonSerializer extends JsonSerializer<Date> {
    @Override
    public void serialize(final Date value, final JsonGenerator gen, final SerializerProvider serializers) throws IOException, JsonProcessingException {
        String formattedDate = value != null ? new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.GERMANY).format(value) : "none";
        gen.writeString(formattedDate);
    }
}

Add Locale to date formatting.