Daniel,
On 8/15/25 12:49 AM, Daniel Schwartz wrote:
Robert (and all),
I will work on answers your various questions. However, I decided to first explore the
comment (by someone) that a servlet can "swallow" an exception, which I take to
mean that it can throw an exception without reporting the exception or terminating the
program.
I have this system running on a PC identified as localhost. The test URL is:
http://localhost:8080/HolidaysRESTJSON-1.0-SNAPSHOT/webresources/holidaysandevents/countries
I ran two tests. First, I wrote in code to throw an SQL exception, which did
get caught in my catch clause, which printed out some messages and a stack
trace. The web browser showed the retrieved list of countries, but nothing
else.
Second, I replaced the line that throws the SQL exception by one that tries to
do a division by zero. This of course was not caught, but it did print out a
stack trace and reported a 505 error in the browser, and the program did
terminate.
I take this to mean that exceptions are not being "swallowed" by my program.
When/if an exception occurs, there is definitely some indication of this, either in the
server.log or the browser. Because I have never seen either of these actions, I'm fairly
sure that my program is not throwing exceptions and all database connections are being
closed immediately after they are used, i.e., no memory leaks in this respect.
The actual code fragments and outputs are copied below.
----------------------------------------------------------------
The code that throws the SQL exception
----------------------------------------------------------------
@GET
@Path("/countries")
@Produces(MediaType.APPLICATION_JSON)
public String getJsonCountries() {
if (TempDataStorage.countryList == null) {
Connection connection = null;
try {
connection = dataSource.getConnection();
System.out.println("countries connection has been opened");
TempDataStorage.countryList = GetCountryList.doIt(connection);
throw new SQLException("testing sql exception");
// connection.close();
// System.out.println("countries connection has been closed");
} catch (SQLException e) {
System.out.println(e);
System.out.println("catching sql exception");
if (connection != null) {
try {
connection.close();
} catch (SQLException ex) {
System.out.println(ex);
}
}
}
}
100% connection leak every time, guaranteed.
You are never closing the connection, because it's been commented out.
Perhaps this was just for testing, because I see you are throwing an
exception.
The conn.close() *MUST* be in a finally {} block. Do not put it in the
try block. Do not put it in the catch block. Always put it in the
finally block.
------------------------------------------------------------------
The output in the server.log file
------------------------------------------------------------------
[2025-08-14T23:34:42.019-0400] [glassfish 4.1] [INFO] [] [] [tid: _ThreadID=40
_ThreadName=Thread-8] [timeMillis: 1755228882019] [levelValue: 800] [[
countries connection has been opened]]
[2025-08-14T23:34:42.022-0400] [glassfish 4.1] [INFO] [] [] [tid: _ThreadID=40
_ThreadName=Thread-8] [timeMillis: 1755228882022] [levelValue: 800] [[
java.sql.SQLException: testing sql exception
at
com.worldholidaysandevents.restjsonwebservice.HolidaysRESTJSONResource.getJsonCountries(HolidaysRESTJSONResource.java:54)
... stack trace ...
[2025-08-14T23:34:42.022-0400] [glassfish 4.1] [INFO] [] [] [tid: _ThreadID=40
_ThreadName=Thread-8] [timeMillis: 1755228882022] [levelValue: 800] [[
catching sql exception]]
... and the server does not crash. You can make any request without
restarting Glassfish, right?
----------------------------------------------------------------
The code that divides by zero
----------------------------------------------------------------
@GET
@Path("/countries")
@Produces(MediaType.APPLICATION_JSON)
public String getJsonCountries() {
if (TempDataStorage.countryList == null) {
Connection connection = null;
try {
connection = dataSource.getConnection();
System.out.println("countries connection has been opened");
TempDataStorage.countryList = GetCountryList.doIt(connection);
float something = 1/0;
connection.close();
System.out.println("countries connection has been closed");
} catch (SQLException e) {
System.out.println(e);
System.out.println("catching sql exception");
if (connection != null) {
try {
connection.close();
} catch (SQLException ex) {
System.out.println(ex);
}
}
}
}
100% connection leak every time, guaranteed.
You are never closing the connection, because your code is throwing an
uncaught exception (divide by zero) Perhaps this was just for testing,
because I see you are intentionally dividing by zero.
The conn.close() *MUST* be in a finally {} block. Do not put it in the
try block. Do not put it in the catch block. Always put it in the
finally block.
-chris
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