We have built a small application based on Apache Httpclient to test the
speed of our database connection. The problem is that we get 'Connection
refused' errors at completely unpredictable moments.
We're creating 50 threads that each wait for a random number of miliseconds
and then do this:
private boolean execute(String argInsurancePolicyNumber) {
boolean result = true;
Connection conn = null;
PreparedStatement stat = null;
ResultSet resultSet = null;
String sql = null;
sql = "select * from sysusr.table1 T1_HINT_K0101 where
DEPT_NR = ? and POL_NR = ? and ING_DTM_OCC <= ? and EIND_DTM_OCC > ?";
try {
conn = this.dataSource.getConnection();
stat = conn.prepareStatement(sql);
stat.setString(1,
argInsurancePolicyNumber.substring(0,2));
stat.setString(2,
argInsurancePolicyNumber.substring(2,8));
stat.setString(3, "20060505");
stat.setString(4, "20060505");
resultSet = stat.executeQuery(); // see below for this
method
}
catch (Throwable t) {
result = false;
t.printStackTrace();
}
finally {
try {
resultSet.close();
}
catch (Throwable t) {
t.printStackTrace();
}
try {
stat.close();
}
catch (Throwable t) {
t.printStackTrace();
}
try {
conn.close();
}
catch (Throwable t) {
t.printStackTrace();
}
}
return result;
}
The 'executeQuery' method eventually does this:
String tijden = "";
byte[] responseBody = null;
int statusCode = 0;
FireXmlParser parser = null;
Object[] result = new Object[2];
this.post = this.createPostMethod("/QW01/W01", 3); // see
below for this method
tijden = Long.toString(System.currentTimeMillis()) + ";";
this.post.addParameter("qedsql", argQuery);
parser = new FireXmlParser();
try {
tijden = tijden +
Long.toString(System.currentTimeMillis()) + ";";
statusCode =
FireXmlHttpURLConnectionApache.client.executeMethod(post);
tijden = tijden +
Long.toString(System.currentTimeMillis()) + ";";
if (statusCode != HttpStatus.SC_OK) {
System.err.println("Method failed: " +
post.getStatusLine());
}
// Read the response body.
responseBody = post.getResponseBody();
tijden = tijden +
Long.toString(System.currentTimeMillis()) + ";";
parser.parse(responseBody);
tijden = tijden +
Long.toString(System.currentTimeMillis()) + ";";
result[0] = parser.getResultSet();
tijden = tijden +
Long.toString(System.currentTimeMillis()) + ";";
}
catch (ConnectException e) {
e.printStackTrace();
System.err.println("Fatal protocol violation: " +
e.getMessage());
result[0] = new SQLException(e.getMessage());
}
catch (HttpException e) {
System.err.println("Fatal protocol violation: " +
e.getMessage());
}
catch (IOException e) {
System.err.println("Fatal transport error: " +
e.getMessage());
}
finally {
post.abort();
post.releaseConnection();
}
result[1] = tijden;
this.post.removeParameter("qedsql");
fireXmlHttpConnectionPoolApache.connectionReady(this);
return result;
The PostMethod is created like this:
private PostMethod createPostMethod(String argPath, int
argNumberOfRecoveries) {
PostMethod post = null;
post = new PostMethod();
post.setPath(argPath);
post.getParams().setParameter(HttpMethodParams.RETRY_HANDLER,
new DefaultHttpMethodRetryHandler(argNumberOfRecoveries, false));
post.addRequestHeader("Connection", "close");
return post;
}
And the HttpClient is created once, upon initialization, like this:
private HttpClient createHttpClient(String argHost, int argPort,
int argMaxTotalConnections) {
HttpClient client = null;
HttpConnectionManagerParams httpConnectionManagerParams = null;
HostConfiguration hostConfiguration = null;
MultiThreadedHttpConnectionManager
multiThreadedHttpConnectionManager = null;
hostConfiguration = new HostConfiguration();
hostConfiguration.setHost(argHost, argPort);
httpConnectionManagerParams = new
HttpConnectionManagerParams();
httpConnectionManagerParams.setStaleCheckingEnabled(false);
httpConnectionManagerParams
.setDefaultMaxConnectionsPerHost(argMaxTotalConnections);
httpConnectionManagerParams.setMaxConnectionsPerHost(hostConfiguration,
argMaxTotalConnections);
httpConnectionManagerParams.setMaxTotalConnections(argMaxTotalConnections);
multiThreadedHttpConnectionManager = new
MultiThreadedHttpConnectionManager();
multiThreadedHttpConnectionManager.setParams(httpConnectionManagerParams);
client = new HttpClient(multiThreadedHttpConnectionManager);
client.setHostConfiguration(hostConfiguration);
return client;
}
Please let me know if this doesn't make sense. I find it hard to decide
what to post and what to leave out.
Sometimes it starts throwing exceptions that look like this:
29-sep-2006 9:53:19 org.apache.commons.httpclient.HttpMethodDirector
executeWithRetry
INFO: I/O exception (java.net.ConnectException) caught when processing
request: Connection refused: connect
If this happens we make it go through three more retries (of necessary).
Sometimes that isn't enough and we get:
java.net.ConnectException: Connection refused: connect
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
at
java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:364)
at java.net.Socket.connect(Socket.java:507)
at java.net.Socket.connect(Socket.java:457)
at java.net.Socket.<init>(Socket.java:365)
at java.net.Socket.<init>(Socket.java:238)
at
org.apache.commons.httpclient.protocol.DefaultProtocolSocketFactory.createSocket(DefaultProtocolSocketFactory.java:79)
at
org.apache.commons.httpclient.protocol.DefaultProtocolSocketFactory.createSocket(DefaultProtocolSocketFactory.java:121)
at
org.apache.commons.httpclient.HttpConnection.open(HttpConnection.java:709)
at
org.apache.commons.httpclient.MultiThreadedHttpConnectionManager$HttpConnectionAdapter.open(MultiThreadedHttpConnectionManager.java:1321)
at
org.apache.commons.httpclient.HttpMethodDirector.executeWithRetry(HttpMethodDirector.java:393)
at
org.apache.commons.httpclient.HttpMethodDirector.executeMethod(HttpMethodDirector.java:171)
at
org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:396)
at
org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:324)
etc.
I have been digging through the mail archives and trying to figure this one
out for more than a week but I still don't understand
what *really* causes a 'connection refused'. I guess that is because there
may be many different causes.
Any clues pointing me in the right direction will be much appreciated.
Regards,
Iris
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