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Asked: 2020-05-11 02:06:30 +0800 CST 2020-05-11 02:06:30 +0800 CST

List<Object> to String in Java

  • 772

I have a List of an Object.

public class BusStop {

    private String description;

    private float lat;

    private float lng;

    //getter and setter

}

Of which I try to put all its content inside a variable of type String.

I have tried this:

StringBuilder aux = new StringBuilder();
busStop.forEach(aux::append);

return aux.toString();

But the response I get is not the desired one.

[email protected]@15820f4bes.yo.app.model.BusStop@2022ad11

And this is just what I want to achieve

[{"lat":43.482243622643026,"lng":-3.7942432892720035,"description":"1"},{"lat":43.47775946266253,"lng":-3.8052296173970035,"description":"2"},{"lat ":43.474520695703184,"lng":-3.822567416469269,"description":"3"}]

java

5 Answers

  1. Best Answer

    The problem is that you are calling the toString() method and you don't have it overridden. If the toString() method is not overridden, the parent method is called (in this case the Object method, father of all) and what it does is show the representation of the class and the object. Here is the documentation about it

    You would have to create the override something like this

    @Override
public String toString(){
 return "{ lat:" + lat + (otras propiedades) +"}"
}
    • 2

  2. One option is to use Streamsand map():

    public List<String> getStringList(List<BusStop> busStopList){
    return busStopList.stream()
           .map(item->getItemAsString(item))
           .collect(Collectors.toList());
}
private String getItemAsString(BusStop busStop){
    StringBuilder text = new StringBuilder();
    text.append("{");
    text.append("lat=").append(lat).append(",");
    text.append("lng=").append(lng).append(",");
    text.append("description=").append(description);
    text.append("}");
    return text.toString();
}
    • 2

  3. You must either override the toString() method of the BusStop class or define a specific one that returns the JSON representation of that instance and call it in that forEach() .

    Example:

    public String generaJSON() {
    String patron = "{\"lat\":%s, \"lng\":%s, \"description\":\"%s\"}";
    return String.format(patron, getLat(), getLng(), getDescription());
}

    Another option would be to look at FasterXML Jackson libraries to convert object instances to JSON strings and vice versa.

    • 1

  4. You can always override the toString() method of the Class, so it could be something like:

    @Override
public String toString() { 
     return "{'lat':" + lat + ",'lng':" + lng + ",'description':'" + description + "'}";
}
    • 1

  5. Try this method in the class BusStop.

    public Staff crearJsonFromObject(BusStop obj) {

        Staff staff = new Staff();

        staff.setLat(obj.getLat());
        staff.setLng(obj.getLng());
        staff.setDescription(obj.getDescription());

        return staff;

    }

    Departure:

    {"lat":3423434,"lng":23424242,"description":"wefwefwf"}
    • 0