Re: HashMap and dynamic JDBC update

Eric Sosman <esosman@ieee-dot-org.invalid>
Fri, 07 Aug 2009 09:05:53 -0400
Alessandro wrote:


I have an HashMap<String, Object> used to save names and values of
fields to be updated via JDBC update in a table. The type of data is
variable according to field name , so I'm using Object ... the idea to
produce update query is as follows but I believe there is a better
method to do it.

     Although I don't know much about JDBC, I can see a few
possibilities for improvement in your code and the Javadoc
suggests a few others. I've reformatted the code because
the amount of indentation in
                            the original
excessive and impairs

public void updateQuery(Session session, String table,
HashMap<String,Object> updateH, String condition) throws Throwable{
        String sQuery="UPDATE " + table + " SET ";
        String keys="";

        Iterator iterator = updateH.keySet().iterator();
            keys= keys + "," + + "= ?";

     A "for each" loop would reduce the visual clutter a bit:

    for (String key : updateH.keySet())
        keys += "," + key + "= ?";

An efficiency fanatic might suggest appending the pieces to a
StringBuilder and only creating a String when all is finished,
but that's probably not worth while: The number of keys in a
query is most likely small, and compared to the amount of work
the database itself must do the time spent mangling strings is
unlikely to be important.

       PreparedStatement ps = session.connection()
               Query keys.substring(1) + " WHERE " + condition);


     The first loop has already exhausted this Iterator, so the
code inside this `while' will never execute. You need to get
a fresh Iterator, or write a new "for each," or combine the two
loops into one. Also, don't you need to maintain a counter to
use in the ps.setXXX() calls?

           Object myObj=updateH.get(;
           if(myObj instanceof String){
           else if (myObj.instanceof Date){
           //etc also for Double, Integer, ..

 > }

     The Javadoc describes a setObject() method; can you use
it instead of this long chain of `instanceof' tests? There's
apparently a standard mapping from Java classes to SQL data
types, and since the examples you show here appear to be of
a fairly "obvious" kind, perhaps the standard mapping will do.

     If it won't, you might be able to use the three-argument
form of setObject(), along with a pre-initialized map of Java
classes to SQL type codes:

    // while initializing ...
    Map<Class,Integer> types = ...;
    types.put(java.util.Date.class, java.sql.Types.DATE);
    types.put(my.package.Thing.class, java.sql.Types.VARBINARY);

    // later, when preparing a query ...
    int index = 1;
    for (String key : updateH.keySet()) {
        Object value = updateH.get(key);
        Integer type = types.get(value.getClass());
        if (type == null) ... // unrecognizable value?
        ps.setObject(index++, value, type);

   catch(Throwable ex){
       throw ex;

     What's the point of this? Why bother to catch it at all,
if all you're going to do is re-throw it unaltered?



Any suggestions ?

     As I mentioned, I'm not experienced with JDBC -- so view
my suggestions with healthy skepticism. "Trust, but verify."

Eric Sosman

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