Is there any way to convert a Map to a JSON representation using Jackson without writing to a file?
jackson, java, json
Solution
Pass your Map to `ObjectMapper.writeValueAsString(Object value)`
It's more efficient than using `StringWriter`, according to the docs:
Method that can be used to serialize any Java value as a String. Functionally equivalent to calling writeValue(Writer,Object) with StringWriter and constructing String, but more efficient.
Example
import org.codehaus.jackson.map.ObjectMapper;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
public class Example {
public static void main(String[] args) throws IOException {
Map<String,String> map = new HashMap<>();
map.put("key1","value1");
map.put("key2","value2");
String mapAsJson = new ObjectMapper().writeValueAsString(map);
System.out.println(mapAsJson);
}
}
Problem
I'm trying to use Jackson to convert a HashMap to a JSON representation. However, all the ways I've seen involve writing to a file and then reading it back, which seems really inefficient. I was wondering if there was anyway to do it directly? Here's an example of an instance where I'd like to do it ``` public static Party readOneParty(String partyName) { Party localParty = new Party(); if(connection==null) { connection = new DBConnection(); } try { String query = "SELECT * FROM PureServlet WHERE PARTY_NAME=?"; ps = con.prepareStatement(query); ps.setString(1, partyName); resultSet = ps.executeQuery(); meta = resultSet.getMetaData(); String columnName, value; resultSet.next(); for(int j=1;j<=meta.getColumnCount();j++) { // necessary to start at j=1 because of MySQL index starting at 1 columnName = meta.getColumnLabel(j); value = resultSet.getString(columnName); localParty.getPartyInfo().put(columnName, value); // this is the hashmap within the party that keeps track of the individual values. The column Name = label, value is the value } } } public class Party { HashMap <String,String> partyInfo = new HashMap<String,String>(); public HashMap<String,String> getPartyInfo() throws Exception { return partyInfo; } } ``` The output would look something like this ``` "partyInfo": { "PARTY_NAME": "VSN", "PARTY_ID": "92716518", "PARTY_NUMBER": "92716518" } ``` So far every example I've come across of using `ObjectMapper` involves writing to a file and then reading it back. Is there a Jackson version of Java's `HashMap` or `Map` that'll work in a similar way to what I have implemented?