ATEST-79:

- implementing first draft of timerange and pulserange queries
- adding tests, again based on an embedded local cassandra instance

src/main/java/ch/psi/daq/rest/ResponseStreamWriter.java

@@ -0,0 +1,112 @@
+/**
+ * 
+ */
+package ch.psi.daq.rest;
+
+import java.io.IOException;
+import java.util.Set;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import javax.servlet.ServletResponse;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Autowired;
+
+import ch.psi.daq.domain.cassandra.DataEvent;
+import ch.psi.daq.rest.queries.AbstractQuery;
+
+import com.fasterxml.jackson.core.JsonEncoding;
+import com.fasterxml.jackson.core.JsonFactory;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.ObjectWriter;
+import com.fasterxml.jackson.databind.ser.impl.SimpleBeanPropertyFilter;
+import com.fasterxml.jackson.databind.ser.impl.SimpleFilterProvider;
+
+/**
+ * Takes a Java 8 stream and writes it to the output stream provided by the {@link ServletResponse}
+ * of the current request.
+ */
+public class ResponseStreamWriter {
+
+   private static final Logger logger = LoggerFactory.getLogger(ResponseStreamWriter.class);
+
+   @Autowired
+   private JsonFactory jsonFactory;
+
+   @Autowired
+   private ObjectMapper mapper;
+
+   /**
+    * Responding with the the contents of the stream by writing into the output stream of the
+    * {@link ServletResponse}.
+    * 
+    * @param stream {@link Stream} instance of {@link DataEvent}s
+    * @param query concrete instance of {@link AbstractQuery}
+    * @param response {@link ServletResponse} instance given by the current HTTP request
+    * @throws IOException thrown if writing to the output stream fails
+    */
+   public void respond(Stream<DataEvent> stream, AbstractQuery query, ServletResponse response) throws IOException {
+
+      Set<String> includedFields = query.getFields();
+
+      if (query.getAggregations() != null) {
+         includedFields.addAll(query.getAggregations()
+               .stream()
+               .map(a -> {
+                  return a.getType().toString();
+               })
+               .collect(Collectors.toSet()));
+      }
+
+      ObjectWriter writer = configureWriter(includedFields);
+
+      respondInternal(stream, response, writer);
+   }
+
+   /**
+    * Configures the writer dynamically by including the fields which should be included in the
+    * response.
+    * 
+    * @param includedFields set of strings which correspond to the getter method names of the
+    *        classes registered as a mixed-in
+    * @return the configured writer that includes the specified fields
+    */
+   private ObjectWriter configureWriter(Set<String> includedFields) {
+      SimpleFilterProvider propertyFilter = new SimpleFilterProvider();
+      propertyFilter.addFilter("namedPropertyFilter", SimpleBeanPropertyFilter.filterOutAllExcept(includedFields));
+      // only write the properties not excluded in the filter
+      ObjectWriter writer = mapper.writer(propertyFilter);
+      return writer;
+   }
+
+   /**
+    * Writes the Java stream into the output stream.
+    * 
+    * @param stream {@link Stream} instance of {@link DataEvent}s
+    * @param response {@link ServletResponse} instance given by the current HTTP request
+    * @param writer configured writer that includes the fields the end user wants to see
+    * @throws IOException thrown if writing to the output stream fails
+    */
+   private void respondInternal(Stream<DataEvent> stream, ServletResponse response, ObjectWriter writer)
+         throws IOException {
+
+      JsonGenerator generator = jsonFactory.createGenerator(response.getOutputStream(), JsonEncoding.UTF8);
+      generator.writeStartArray();
+      stream.forEach(ds -> {
+         try {
+            logger.trace("Writing value for: {}", ds);
+            // use the writer created just before
+            writer.writeValue(generator, ds);
+         } catch (Exception e) {
+            logger.error("", e);
+         }
+      });
+      generator.writeEndArray();
+      generator.flush();
+      generator.close();
+   }
+
+}