Question

I have a EnumMap:

EnumMap<Gender, Integer> genderMap = new EnumMap(Gender.class);

where Gender is public enum Gender {Male, Female};

And I have req.setAttribute("genderMap", genderMap);

Now I want to get the value from genderMap by a key in JSP file:

${genderMap['Male']}

but this doesn’t get the value in genderMap. Why?

Answer 1

Don’t use enum mappings. Just use enums as enums in Java and as strings in JSP/EL.

I’ll assume that you need that integer because of a database mapping. E.g. Male is stored as 1 in database and Female is stored as 0 in database. In that case, you need to redesign your enum as follows:

public enum Gender {

    Male(1), Female(0);

    private int id;

    private Gender(int id) { 
        this.id = id;
    }

    public int getId() {
        return id;
    }

    public static Gender valueOf(int id) {
        for (Gender gender : values()) {
            if (gender.id == id) {
                return gender;
            }
        }

        return null;
    }

}

When populating the Person from DB by JDBC, just do

person.setGender(Gender.valueOf(resultSet.getInt("gender")));

When showing preselected options to enduser in JSP, just do

request.setAttribute("genders", Gender.values());

and

Gender:<br/>
<c:forEach items="${genders}" var="gender">
    <input type="radio" id="gender_${gender.id}" name="gender" value="${gender.id}" 
        ${gender == person.gender ? 'checked="checked"' : ''} />
    <label for="gender_${gender.id}">${gender}</label>
    <br />
</c:forEach>

or even without the id

Gender:<br/>
<c:forEach items="${genders}" var="gender">
    <input type="radio" id="gender_${gender}" name="gender" value="${gender}" 
        ${gender == person.gender ? 'checked="checked"' : ''} />
    <label for="gender_${gender}">${gender}</label>
    <br />
</c:forEach>

When collecting submitted values in servlet, just do

Gender gender = Gender.valueOf(Integer.valueOf(request.getParameter("gender")));

or when using without id in HTML

Gender gender = Gender.valueOf(request.getParameter("gender"));