如何在Java中检查null值？

Question

How to look for the value whether it is null or not in JSP. Eg in below I want to check the description column in pipe table for null values.

String Query1 = "SELECT description FROM pipe where pipe_id='" + id+"' and version_id=2";
SQLResult = SQLStatement.executeQuery(Query1);
SQLResult.first();
description = SQLResult.getString("description");
if(description=="")
{
    json_string=json_string+"&desc="+description;
    out.println("not null");
} else
{
    json_string=json_string;
    out.println("null");
}

Answer 1

Well: if (description != null && !description.isEmpty()) ... however are you writing this code within a JSP ? That seems wrong. You should probably do this stuff within a servlet and pass the description as an request attribute to a jsp.

Answer 2

或者，您可以使用StringUtils.isNotEmpty(description) 。

Answer 3

如果您确实在使用jsp，则应将描述存储在request属性中，然后使用<c:if test="${empty description}"> 。

Answer 4

I use this personal method:

public static boolean isNullOrEmpty(Object obj) {
    if (obj == null || obj.toString().length() < 1 || obj.toString().equals(""))
        return true;
    return false;
}