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Added encoder for encoding strings in JSON format
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‎pom.xml

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<artifactId>jdom</artifactId>
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<version>1.1</version>
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</dependency>
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<dependency>
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<groupId>com.fasterxml.jackson.core</groupId>
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<artifactId>jackson-core</artifactId>
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<version>2.1.4</version>
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</dependency>
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</dependencies>
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‎src/main/java/org/culturegraph/mf/stream/converter/JsonEncoder.java

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/*
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* Copyright 2013 Deutsche Nationalbibliothek
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*
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* Licensed under the Apache License, Version 2.0 the "License";
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.culturegraph.mf.stream.converter;
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import java.io.IOException;
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import java.io.StringWriter;
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import org.culturegraph.mf.exceptions.MetafactureException;
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import org.culturegraph.mf.framework.DefaultStreamPipe;
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import org.culturegraph.mf.framework.ObjectReceiver;
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import org.culturegraph.mf.framework.StreamReceiver;
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import org.culturegraph.mf.framework.annotations.Description;
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import org.culturegraph.mf.framework.annotations.In;
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import org.culturegraph.mf.framework.annotations.Out;
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import com.fasterxml.jackson.core.JsonFactory;
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import com.fasterxml.jackson.core.JsonGenerationException;
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import com.fasterxml.jackson.core.JsonGenerator;
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import com.fasterxml.jackson.core.JsonStreamContext;
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/**
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* Serialises an object as JSON. Records and entities are represented
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* as objects unless their name ends with []. If the name ends with [],
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* an array is created.
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*
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* @author Christoph Böhme
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*
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*/
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@Description("Serialises an object as JSON")
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@In(StreamReceiver.class)
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@Out(String.class)
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public final class JsonEncoder extends
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DefaultStreamPipe<ObjectReceiver<String>> {
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public static final String ARRAY_MARKER = "[]";
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private final JsonGenerator jsonGenerator;
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private final StringWriter writer = new StringWriter();
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public JsonEncoder() {
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try {
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jsonGenerator = new JsonFactory().createGenerator(writer);
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} catch (IOException e) {
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throw new MetafactureException(e);
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}
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}
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@Override
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public void startRecord(final String id) {
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final StringBuffer buffer = writer.getBuffer();
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buffer.delete(0, buffer.length());
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startGroup(id);
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}
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@Override
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public void endRecord() {
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endGroup();
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try {
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jsonGenerator.flush();
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} catch (IOException e) {
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throw new MetafactureException(e);
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}
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getReceiver().process(writer.toString());
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}
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@Override
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public void startEntity(final String name) {
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startGroup(name);
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}
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@Override
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public void endEntity() {
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endGroup();
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}
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@Override
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public void literal(final String name, final String value) {
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try {
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if (jsonGenerator.getOutputContext().inObject()) {
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jsonGenerator.writeFieldName(name);
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}
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if (value == null) {
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jsonGenerator.writeNull();
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} else {
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jsonGenerator.writeString(value);
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}
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} catch (JsonGenerationException e) {
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throw new MetafactureException(e);
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}
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catch (IOException e) {
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throw new MetafactureException(e);
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}
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}
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private void startGroup(final String name) {
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try {
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final JsonStreamContext ctx = jsonGenerator.getOutputContext();
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if (name.endsWith(ARRAY_MARKER)) {
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if (!ctx.inRoot()) {
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jsonGenerator.writeFieldName(name.substring(0, name.length() - ARRAY_MARKER.length()));
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}
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jsonGenerator.writeStartArray();
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} else {
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if (!ctx.inRoot()) {
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jsonGenerator.writeFieldName(name);
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}
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jsonGenerator.writeStartObject();
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}
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} catch (JsonGenerationException e) {
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throw new MetafactureException(e);
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}
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catch (IOException e) {
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throw new MetafactureException(e);
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}
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}
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private void endGroup() {
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try {
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final JsonStreamContext ctx = jsonGenerator.getOutputContext();
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if (ctx.inObject()) {
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jsonGenerator.writeEndObject();
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} else if (ctx.inArray()) {
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jsonGenerator.writeEndArray();
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}
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} catch (JsonGenerationException e) {
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throw new MetafactureException(e);
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}
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catch (IOException e) {
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throw new MetafactureException(e);
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}
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}
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}

‎src/test/java/org/culturegraph/mf/stream/converter/JsonEncoderTest.java

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/*
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* Copyright 2013 Deutsche Nationalbibliothek
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*
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* Licensed under the Apache License, Version 2.0 the "License";
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.culturegraph.mf.stream.converter;
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import static org.junit.Assert.assertEquals;
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import org.culturegraph.mf.framework.DefaultObjectReceiver;
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import org.junit.Test;
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/**
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* Test for {@link JsonEncoder}.
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*
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* @author Christoph Böhme
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*
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*/
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public final class JsonEncoderTest {
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private static final String SIMPLE_JSON = "{\"lit1\":\"val1\",\"ent1\":{\"lit2\":\"val2\",\"lit3\":\"val3\"}}";
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private static final String LIST_JSON = "{\"list\":[\"1\",\"2\",\"3\"],\"lit\":\"val\"}";
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@Test
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public void testSimpleJson() {
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final JsonEncoder encoder = new JsonEncoder();
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encoder.setReceiver(new DefaultObjectReceiver<String>() {
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@Override
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public void process(final String str) {
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assertEquals(SIMPLE_JSON, str);
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}
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});
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encoder.startRecord("");
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encoder.literal("lit1", "val1");
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encoder.startEntity("ent1");
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encoder.literal("lit2", "val2");
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encoder.literal("lit3", "val3");
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encoder.endEntity();
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encoder.endRecord();
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encoder.closeStream();
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}
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@Test
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public void testListJson() {
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final JsonEncoder encoder = new JsonEncoder();
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encoder.setReceiver(new DefaultObjectReceiver<String>() {
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@Override
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public void process(final String str) {
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assertEquals(LIST_JSON, str);
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}
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});
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encoder.startRecord("");
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encoder.startEntity("list[]");
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encoder.literal("", "1");
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encoder.literal("", "2");
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encoder.literal("", "3");
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encoder.endEntity();
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encoder.literal("lit", "val");
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encoder.endRecord();
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encoder.closeStream();
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}
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}

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