如何对自定义Jackson JsonSerializer进行单元测试？

Question

我写了以下内容JsonSerializer让Jackson将一个整数数组序列化为JSON:

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import java.io.IOException;

public class TalkIdsSerializer extends JsonSerializer<TalkIds> {

    /**
     * Serializes a TalkIds object into the following JSON string:
     * Example: { "talk_ids" : [ 5931, 5930 ] }
     */
    @Override
    public void serialize(TalkIds talkIds, JsonGenerator jsonGenerator, 
        SerializerProvider provider)
            throws IOException {
        jsonGenerator.writeStartObject();
        jsonGenerator.writeArrayFieldStart(TalkIds.API_DICTIONARY_KEY);
        for (Integer talkId : talkIds.getTalkIds()) {
            jsonGenerator.writeNumber(talkId);
        }
        jsonGenerator.writeEndArray();
        jsonGenerator.writeEndObject();
    }

}

该类在这里使用:

@JsonSerialize(using = TalkIdsSerializer.class)
public class TalkIds { /* ...  */ }

我想测试序列化器的行为,并提出以下内容:

import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerator;
import org.junit.Before;
import org.junit.Test;    
import java.io.IOException;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.Arrays;
import static org.junit.Assert.assertNotNull;
import static org.junit.Assert.assertTrue;

public class TalkIdsSerializerTest {

    protected final ArrayList<Integer> TALK_IDS = 
        new ArrayList<>(Arrays.asList(5931, 5930));

    protected TalkIdsSerializer talkIdsSerializer;

    @Before
    public void setup() throws IOException {
        talkIdsSerializer = new TalkIdsSerializer();
    }

    @Test
    public void testSerialize() throws IOException {
        StringWriter stringWriter = new StringWriter();
        JsonGenerator jsonGenerator = 
            new JsonFactory().createGenerator(stringWriter);
        TalkIds talkIds = new TalkIds();
        talkIds.add(TALK_IDS);
        talkIdsSerializer.serialize(talkIds, jsonGenerator, null);
        String string = stringWriter.toString(); // string is ""
        assertNotNull(string);
        assertTrue(string.length() > 0);
        stringWriter.close();
    }

}

但是,没有任何内容写入StringWriter.我究竟做错了什么？

Answer 1

你需要flush()发电机

调用的方法是将任何缓冲的内容刷新到底层目标(输出流,编写器),以及刷新目标本身.
http://fasterxml.github.io/jackson-core/javadoc/2.1.0/com/fasterxml/jackson/core/JsonGenerator.html#flush()