Java tutorial
/* * Copyright 2013, 2014 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.io.IOException; import java.io.StringWriter; import org.apache.commons.lang.StringEscapeUtils; import org.culturegraph.mf.exceptions.MetafactureException; 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.FluxCommand; import org.culturegraph.mf.framework.annotations.In; import org.culturegraph.mf.framework.annotations.Out; import com.fasterxml.jackson.core.JsonFactory; import com.fasterxml.jackson.core.JsonGenerationException; import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.core.JsonStreamContext; import com.fasterxml.jackson.core.SerializableString; import com.fasterxml.jackson.core.io.CharacterEscapes; import com.fasterxml.jackson.core.io.SerializedString; /** * 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 Christoph Bhme * @author Michael Bchner * */ @Description("Serialises an object as JSON") @In(StreamReceiver.class) @Out(String.class) @FluxCommand("encode-json") public final class JsonEncoder extends DefaultStreamPipe<ObjectReceiver<String>> { public static final String ARRAY_MARKER = "[]"; private final JsonGenerator jsonGenerator; private final StringWriter writer = new StringWriter(); public JsonEncoder() { try { jsonGenerator = new JsonFactory().createGenerator(writer); jsonGenerator.setRootValueSeparator(null); } catch (final IOException e) { throw new MetafactureException(e); } } public void setPrettyPrinting(final boolean prettyPrinting) { if (prettyPrinting) { jsonGenerator.useDefaultPrettyPrinter(); } else { jsonGenerator.setPrettyPrinter(null); } } public boolean getPrettyPrinting() { return jsonGenerator.getPrettyPrinter() != null; } /** * By default JSON output does only have escaping where it is strictly * necessary. This is recommended in the most cases. Nevertheless it can * be sometimes useful to have some more escaping. With this method it is * possible to use {@link StringEscapeUtils#escapeJavaScript(String)}. * * @param escapeCharacters an array which defines which characters should be * escaped and how it will be done. See * {@link CharacterEscapes}. In most cases this should * be null. Use like this: * <pre>{@code int[] esc = CharacterEscapes.standardAsciiEscapesForJSON(); * // and force escaping of a few others: * esc['\''] = CharacterEscapes.ESCAPE_STANDARD; * JsonEncoder.useEscapeJavaScript(esc); * }</pre> */ public void setJavaScriptEscapeChars(final int[] escapeCharacters) { final CharacterEscapes ce = new CharacterEscapes() { private static final long serialVersionUID = 1L; @Override public int[] getEscapeCodesForAscii() { if (escapeCharacters == null) { return CharacterEscapes.standardAsciiEscapesForJSON(); } return escapeCharacters; } @Override public SerializableString getEscapeSequence(final int ch) { final String chString = Character.toString((char) ch); final String jsEscaped = StringEscapeUtils.escapeJavaScript(chString); return new SerializedString(jsEscaped); } }; jsonGenerator.setCharacterEscapes(ce); } @Override public void startRecord(final String id) { final StringBuffer buffer = writer.getBuffer(); buffer.delete(0, buffer.length()); startGroup(id); } @Override public void endRecord() { endGroup(); try { jsonGenerator.flush(); } catch (final IOException e) { throw new MetafactureException(e); } getReceiver().process(writer.toString()); } @Override public void startEntity(final String name) { startGroup(name); } @Override public void endEntity() { endGroup(); } @Override public void literal(final String name, final String value) { try { final JsonStreamContext ctx = jsonGenerator.getOutputContext(); if (ctx.inObject()) { jsonGenerator.writeFieldName(name); } if (value == null) { jsonGenerator.writeNull(); } else { jsonGenerator.writeString(value); } } catch (final JsonGenerationException e) { throw new MetafactureException(e); } catch (final IOException e) { throw new MetafactureException(e); } } private void startGroup(final String name) { try { final JsonStreamContext ctx = jsonGenerator.getOutputContext(); if (name.endsWith(ARRAY_MARKER)) { if (ctx.inObject()) { jsonGenerator.writeFieldName(name.substring(0, name.length() - ARRAY_MARKER.length())); } jsonGenerator.writeStartArray(); } else { if (ctx.inObject()) { jsonGenerator.writeFieldName(name); } jsonGenerator.writeStartObject(); } } catch (final JsonGenerationException e) { throw new MetafactureException(e); } catch (final IOException e) { throw new MetafactureException(e); } } private void endGroup() { try { final JsonStreamContext ctx = jsonGenerator.getOutputContext(); if (ctx.inObject()) { jsonGenerator.writeEndObject(); } else if (ctx.inArray()) { jsonGenerator.writeEndArray(); } } catch (final JsonGenerationException e) { throw new MetafactureException(e); } catch (final IOException e) { throw new MetafactureException(e); } } }