com.brettonw.servlet.Base Maven / Gradle / Ivy
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ServletBase provides a base implementation for a JSON request/response server.
package com.brettonw.servlet;
import com.brettonw.bag.*;
import com.brettonw.bag.formats.MimeType;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.nio.charset.StandardCharsets;
import java.util.HashMap;
import java.util.Map;
import static com.brettonw.servlet.Keys.*;
public class Base extends HttpServlet {
private static final Logger log = LogManager.getLogger (Base.class);
private static ServletContext context;
public static ServletContext getContext () {
return context;
}
public static Object getAttribute (String key) {
return (context != null) ? context.getAttribute (key) : null;
}
public static Object setAttribute (String key, Object value) {
if (context != null) {
Object oldValue = context.getAttribute (key);
context.setAttribute (key, value);
return oldValue;
}
return null;
}
private final Map handlers;
protected BagObject api;
protected Base () {
// try to load the schema and wire up the handlers
handlers = new HashMap<> ();
if ((api = BagObjectFrom.resource (getClass (), "/api.json")) != null) {
// autowire... loop over the elements in the schema, looking for functions that match
// the signature, "handleEventXXX"
String[] eventNames = api.getBagObject (EVENTS).keys ();
for (String eventName : eventNames) {
install (eventName);
}
} else {
log.error ("Failed to load API");
}
}
@Override
public void init (ServletConfig config) throws ServletException {
super.init (config);
context = config.getServletContext ();
log.debug ("STARTING " + context.getServletContextName ());
setAttribute (SERVLET, this);
}
@Override
public void destroy () {
super.destroy ();
log.debug (context.getServletContextName () + " DESTROYING...");
}
@Override
public void doGet (HttpServletRequest request, HttpServletResponse response) throws IOException {
BagObject query = BagObjectFrom.string (request.getQueryString (), MimeType.URL, () -> new BagObject ());
handleRequest (query, request, response);
}
@Override
public void doPost (HttpServletRequest request, HttpServletResponse response) throws IOException {
// get the request data type, then tease out the response type (use a default if it's not present) and the
// charset (if given, otherwise default to UTF-8, because that's what it will be in Java)
String mimeType = MimeType.DEFAULT;
String contentTypeHeader = request.getHeader (CONTENT_TYPE);
if (contentTypeHeader != null) {
String[] contentType = contentTypeHeader.replace (" ", "").split (";");
mimeType = contentType[0];
log.debug ("'Content-Type' is (" + mimeType + ")");
} else {
log.warn ("'Content-Type' is not set by the requestor, using default (" + mimeType + ")");
}
// extract the bag data that's been posted, we do it this roundabout way because
// we don't know a priori if it's an object or array
SourceAdapter sourceAdapter = new SourceAdapterReader(request.getInputStream (), mimeType);
String requestString = sourceAdapter.getStringData ();
Bag postData = BagObjectFrom.string (requestString, mimeType);
if (postData == null) postData = BagArrayFrom.string (requestString);
// handle the query part normally, but add the post data to it (if any)
BagObject query = BagObjectFrom.string (request.getQueryString (), MimeType.URL, () -> new BagObject ())
.put (POST_DATA, postData);
handleRequest (query, request, response);
}
private void handleRequest (BagObject query, HttpServletRequest request, HttpServletResponse response) throws IOException {
Event event = handleEvent (query, request);
String UTF_8 = StandardCharsets.UTF_8.name ();
response.setContentType (MimeType.JSON + "; charset=" + UTF_8);
response.setCharacterEncoding (UTF_8);
PrintWriter out = response.getWriter ();
out.println (event.getResponse ().toString (MimeType.JSON));
out.close ();
}
private Event handleEvent (BagObject query, HttpServletRequest request) {
Event event = new Event (query, request);
if (api != null) {
// create the event object around the request parameters, and validate that it is
// a known event
String eventName = event.getEventName ();
if (eventName != null) {
BagObject eventSpecification = api.getBagObject (Key.cat (EVENTS, eventName));
if (eventSpecification != null) {
// validate the query parameters
BagObject parameterSpecification = eventSpecification.getBagObject (PARAMETERS);
boolean strict = eventSpecification.getBoolean (STRICT, () -> true);
BagArray validationErrors = new BagArray ();
if (strict) {
// loop over the query parameters to be sure they are all valid
String[] queryParameters = query.keys ();
for (int i = 0; i < queryParameters.length; ++i) {
String queryParameter = queryParameters[i];
if (!queryParameter.equals (EVENT)) {
if ((parameterSpecification == null) || (!parameterSpecification.has (queryParameter))) {
validationErrors.add ("Unspecified parameter: '" + queryParameter + "'");
}
}
}
}
// loop over the parameter specification to be sure all of the required ones are present
if (parameterSpecification != null) {
String[] expectedParameters = parameterSpecification.keys ();
for (int i = 0; i < expectedParameters.length; ++i) {
String expectedParameter = expectedParameters[i];
if (parameterSpecification.getBoolean (Key.cat (expectedParameter, REQUIRED), () -> false)) {
if (!query.has (expectedParameter)) {
validationErrors.add ("Missing required parameter: '" + expectedParameter + "'");
}
}
}
}
// if the validation passed
if (validationErrors.getCount () == 0) {
// get the handler, and try to take care of business...
Handler handler = handlers.get (eventName);
if (handler != null) {
// finally, do your business
handler.handle (event);
} else {
event.error ("No handler installed for '" + EVENT + "' (" + eventName + ")");
}
} else {
event.error (validationErrors);
}
} else {
event.error ("Unknown '" + EVENT + "' (" + eventName + ")");
}
} else {
event.error ("Missing '" + EVENT + "'");
}
} else {
event.error ("Missing API");
}
return event;
}
public boolean install (String eventName) {
try {
Handler handler = new Handler (eventName, this);
handlers.put (handler.getEventName (), handler);
log.info ("Installed '" + handler.getMethodName () + "'");
return true;
} catch (NoSuchMethodException exception) {
log.error ("Install '" + EVENT + "' failed for (" + eventName + ")", exception);
return false;
}
}
// default handlers
public void handleEventOk (Event event) {
event.ok ();
}
public void handleEventHelp (Event event) {
event.ok (api);
}
public void handleEventVersion (Event event) {
event.ok (BagObject
.open (POM_VERSION, getClass ().getPackage ().getImplementationVersion ())
.put (POM_NAME, getClass ().getPackage ().getImplementationTitle ())
.put (DISPLAY_NAME, context.getServletContextName ())
);
}
public void handleEventMultiple (Event event) {
BagArray eventsArray = event.getQuery ().getBagArray (POST_DATA);
if (eventsArray != null) {
int eventCount = eventsArray.getCount ();
BagArray results = new BagArray (eventCount);
for (int i = 0; i < eventCount; ++i) {
Event subEvent = handleEvent (eventsArray.getBagObject (i), event.getRequest ());
results.add (subEvent.getResponse ());
}
event.ok (results);
} else {
event.error ("No events found (expected an array in '" + POST_DATA + "')");
}
}
}
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