No serializer found for class using Json

Question

I have a basic SpringBoot 2.1.2.RELEASE app. Using Spring Initializer, JPA, embedded Tomcat, Thymeleaf template engine, and package as an executable JAR with a restful architecture

I have this object that I return in a RestMethod:

public class MenuAlarm {



    /**
     * 
     */
    public MenuAlarm() {
        super();
    }


    /**
     * 
     */
    public MenuAlarm(Menu menu) {

        this.menuAlias = menu.getName();
        this.menuId = menu.getId();

        menu
            .getAlerts()
            .forEach(a -> alarms.add(new Alarm(a)));

    }

    class Alarm {

        public Alarm(MenuAlert menuAlert) {

            this.percentage = menuAlert.getPercentage();

            if (menuAlert.getCriteria() > 1) {
                this.increase = true;
            } else {
                this.increase = false;
            }
            this.enabled = menuAlert.isEnabled();
        }

        public Alarm() {
            super();
        }

        Integer percentage;

        boolean increase;

        boolean enabled;

    }

    String menuAlias;

    Long menuId;

    List<Alarm> alarms = new ArrayList<Alarm>();

    public String getMenuAlias() {
        return menuAlias;
    }

    public void setMenuAlias(String menuAlias) {
        this.menuAlias = menuAlias;
    }

    public Long getMenuId() {
        return MenuId;
    }

    public void setMenuId(Long menuId) {
        this.menuId = menuId;
    }

    public List<Alarm> getAlarms() {
        return alarms;
    }

    public void setAlarms(List<Alarm> alarms) {
        this.alarms = alarms;
    }
}

but when I return the result I got this error:

Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class com.tdk.api.json.MenuAlarm$Alarm and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: com.tdk.api.json.UserAlerts[“menuAlarms"]->java.util.ArrayList[0]->com.tdk.api.json.MenuAlarm["alarms"]->java.util.ArrayList[0])`

Answer 1

You haven't told Jackson how to serialize the inner Alarm class.

Jackson will attempt to serialize it as a bean (thus the reference to BeanSerializer), but you haven't provided any JavaBeans-compatible getter methods on Alarm.

Your options are to either to write a custom serializer for Alarm, or add some public getter methods like getPercentage.