Library independent Json encoder added

Author: mgeipel

src/main/java/org/culturegraph/mf/stream/converter/SimpleJsonEncoder.java

@@ -0,0 +1,119 @@
+/*
+ *  Copyright 2013 Deutsche Nationalbibliothek
+ *
+ *  Licensed under the Apache License, Version 2.0 the "License";
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.culturegraph.mf.stream.converter;
+
+import java.util.Deque;
+import java.util.LinkedList;
+
+import org.apache.commons.lang.StringEscapeUtils;
+import org.culturegraph.mf.framework.DefaultStreamPipe;
+import org.culturegraph.mf.framework.ObjectReceiver;
+import org.culturegraph.mf.framework.StreamReceiver;
+import org.culturegraph.mf.framework.annotations.Description;
+import org.culturegraph.mf.framework.annotations.In;
+import org.culturegraph.mf.framework.annotations.Out;
+
+/**
+ * Serialises an object as JSON. Records and entities are represented as objects
+ * unless their name ends with []. If the name ends with [], an array is
+ * created.
+ * 
+ * @author Markus Geipel
+ * 
+ */
+@Description("Serialises an object as JSON")
+@In(StreamReceiver.class)
+@Out(String.class)
+public final class SimpleJsonEncoder extends DefaultStreamPipe<ObjectReceiver<String>> {
+
+	public static final String ARRAY_MARKER = "[]";
+
+	private StringBuilder builder = new StringBuilder();
+	private final Deque<Character> bracketStack = new LinkedList<Character>();
+	private final Deque<Boolean> commaStack = new LinkedList<Boolean>();
+	private boolean commaNeeded;
+
+
+	@Override
+	public void startRecord(final String id) {
+		builder.append('{');
+		bracketStack.push(Character.valueOf('}'));
+	}
+
+	@Override
+	public void endRecord() {
+		builder.append('}');
+		bracketStack.clear();
+		getReceiver().process(builder.toString());
+		builder = new StringBuilder();
+		commaStack.clear();
+	}
+
+	@Override
+	public void startEntity(final String name) {
+
+		if (commaNeeded) {
+			builder.append(", ");
+		}
+		commaNeeded = true;
+
+		if (name.endsWith(ARRAY_MARKER)) {
+			builder.append("\"" + escape(name.substring(0, name.length() - ARRAY_MARKER.length())) + "\": [ ");
+			bracketStack.push(Character.valueOf(']'));
+		} else {
+			if (inArray()) {
+				builder.append(" { ");
+			} else {
+				builder.append("\"" + escape(name) + "\": { ");
+			}
+
+			bracketStack.push(Character.valueOf('}'));
+		}
+		commaStack.push(Boolean.valueOf(commaNeeded));
+		commaNeeded = false;
+	}
+
+	private static String escape(final String string) {
+		return StringEscapeUtils.escapeJavaScript(string);
+	}
+
+	@Override
+	public void endEntity() {
+		builder.append(bracketStack.pop() + " ");
+		commaNeeded = commaStack.pop().booleanValue();
+	}
+
+	@Override
+	public void literal(final String name, final String value) {
+
+		if (commaNeeded) {
+			builder.append(", ");
+		}
+
+		if (inArray()) {
+			builder.append("\"" + escape(value) + "\"");
+		} else {
+			builder.append("\"" + escape(name) + "\":\"" + escape(value) + "\"");
+		}
+
+		commaNeeded = true;
+	}
+
+	private boolean inArray() {
+		return bracketStack.peek().charValue() == ']';
+	}
+
+}