如何在不通过ObjectMapper时在JsonParser上设置ObjectCodec？

Question

注意:这是使用Jackson 2.3.2

为了满足我的一个项目的需要,我正在编写一个自定义文件JsonParser,它记录了Map键的位置JsonPointer和值是Integers(指针指向的行号).

该课程名为LineRecorderJsonParser.它是由LineRecorderJsonFactory一个简单的代表产生的:

public final class LineRecorderJsonFactory
    extends JsonFactory
{
    @Override
    protected JsonParser _createParser(final InputStream in,
        final IOContext ctxt)
        throws IOException, JsonParseException
    {
        final JsonParser parser = super._createParser(in, ctxt);
        return new LineRecorderJsonParser(parser);
    }

    @Override
    protected JsonParser _createParser(final Reader r, final IOContext ctxt)
        throws IOException, JsonParseException
    {
        final JsonParser parser = super._createParser(r, ctxt);
        return new LineRecorderJsonParser(parser);
    }

    @Override
    protected JsonParser _createParser(final byte[] data, final int offset,
        final int len, final IOContext ctxt)
        throws IOException, JsonParseException
    {
        final JsonParser parser = super._createParser(data, offset, len, ctxt);
        return new LineRecorderJsonParser(parser);
    }
}

我已使用以下代码测试了代码的工作原理:

public static void main(final String... args)
    throws IOException
{
    final JsonFactory factory = new LineRecorderJsonFactory();
    final ObjectMapper mapper = new ObjectMapper(factory);
    final Closer closer = Closer.create();
    final InputStream in;

    try {
        in = closer.register(LineTesting.class.getResourceAsStream
            ("/testfile.json"));
        mapper.readTree(in);
    } finally {
        closer.close();
    }
}

但现在我想测试一下; 所以我写了以下测试代码:

public final class LineRecorderJsonParserTest
{
    private static final String INCORRECT_LINE_INFO
        = "generated line info is incorrect; expected: %s, actual: %s";

    private JsonFactory factory;
    private ObjectMapper mapper;

    @BeforeMethod
    public void initFactory()
    {
        factory = new LineRecorderJsonFactory();
        mapper = new ObjectMapper();
    }

    @DataProvider
    public Iterator<Object[]> getLineData()
    {
        final List<Object[]> list = Lists.newArrayList();

        list.add(new Object[] { "1" });
        return list.iterator();
    }

    @Test(dataProvider = "getLineData")
    public void lineNumbersAreCorrectlyReported(final String subdir)
        throws IOException
    {
        final String basePath = "/parser/" + subdir + '/';
        final Closer closer = Closer.create();
        final TypeReference<Map<JsonPointer, Integer>> typeRef
            = new TypeReference<Map<JsonPointer, Integer>>() {};

        final InputStream input, lines;
        final Map<JsonPointer, Integer> actual, expected;
        final LineRecorderJsonParser parser;

        try {
            input = closer.register(inputFrom(basePath + "input.json"));
            lines = closer.register(inputFrom(basePath + "lines.json"));

            expected = mapper.readValue(lines, typeRef);

            parser = (LineRecorderJsonParser) factory.createParser(input);
            //parser.setCodec(factory.getCodec()); // Doesn't change anything...
            parser.readValueAsTree(); // FAILS HERE
            actual = parser.getLineInfo();

            assertEquals(actual, expected,
                String.format(INCORRECT_LINE_INFO, expected, actual));
        } catch (IOException e) {
            throw closer.rethrow(e);
        } finally {
            closer.close();
        }
    }

    private static InputStream inputFrom(final String path)
    {
        return LineRecorderJsonParserTest.class.getResourceAsStream(path);
    }
}

不幸的是,这不起作用.我得到以下异常:

java.lang.IllegalStateException: No ObjectCodec defined for the parser, can not deserialize JSON into JsonNode tree
    at com.fasterxml.jackson.core.JsonParser.readValueAsTree(JsonParser.java:1507)
    at com.fasterxml.jackson.core.util.JsonParserDelegate.readValueAsTree(JsonParserDelegate.java:371)
    at com.github.fge.jackson.parse.LineRecorderJsonParserTest.lineNumbersAreCorrectlyReported(LineRecorderJsonParserTest.java:84)

即使我(尝试和)设置ObjectCodec自己(见代码),我得到这个例外...

我究竟做错了什么？我如何测试这个类,因为当你ObjectMapper直接阅读时,你没有机会获取底层的解析器？

Answer 1

或者,JsonFactory.setCodec(mapper).

Answer 2

好吧，我在问这个问题几分钟后就发现了如何做到这一点......如果它对其他人有用，我会回答自己。

首先，我JsonFactory的.getCodec()恢复null; 而JsonParser如果你试着给它一个空编解码器不骂你。

其次，ObjectMapperextends ObjectCodec，并且ObjectCodec 有一种读取树的方法（实际上，它具有您通常在 上使用的所有方法ObjectMapper）。

因此，将代码更改为此有效：

parser = (LineRecorderJsonParser) factory.createParser(input);
mapper.readTree(parser);
actual = parser.getLineInfo();