Jackson YAML 序列化对象数组格式

Question

我正在尝试以某种方式格式化我的 Jackson Yaml 序列化。

employees:
 - name: John
   age: 26
 - name: Bill
   age: 17

但是，当我序列化对象时，这是我得到的格式。

employees:
 -
  name: John
  age: 26
 -
  name: Bill
  age: 17

有什么方法可以去掉数组中对象开头的换行符吗？这纯粹是个人 preference/human 可读性问题。

这些是我当前在 YAMLFactory 上设置的属性：

YAMLFactory yamlFactory = new YAMLFactory()
                .enable(YAMLGenerator.Feature.MINIMIZE_QUOTES) //removes quotes from strings
                .disable(YAMLGenerator.Feature.WRITE_DOC_START_MARKER)//gets rid of -- at the start of the file.
                .enable(YAMLGenerator.Feature.INDENT_ARRAYS);// enables indentation.

我查看了 Jackson 中 YAMLGenerator 的 java 文档，并查看了关于 Whosebug 的其他问题，但我找不到一个选项来做我想做的事情。

我已经尝试了 CANONICAL_OUTPUT、SPLIT_LINES 和 LITERAL_BLOCK_STYLE 属性，最后一个在设置 MINIMIZE_QUOTES 时自动设置。 CANONICAL_OUTPUT 似乎在数组周围添加了括号。 SPLIT_LINES 和 LITERAL_BLOCK_STYLE 与多行字符串的处理方式有关。

Answer 1

简短的回答是目前没有办法通过 Jackson 做到这一点。这是由于 snakeyaml 中的一个错误，如果您设置 indicatorIndent 属性，则空格未正确处理，因此 snakeyaml 添加了新行。

我找到了直接使用 snakeyaml 的解决方法。

//The representer allows us to ignore null properties, and to leave off the class definitions
Representer representer = new Representer() {
    //ignore null properties
    @Override
    protected NodeTuple representJavaBeanProperty(Object javaBean, Property property, Object propertyValue, Tag customTag) {
        // if value of property is null, ignore it.
        if (propertyValue == null) {
            return null;
        }
        else {
            return super.representJavaBeanProperty(javaBean, property, propertyValue, customTag);
        }
    }

    //Don't print the class definition
    @Override
    protected MappingNode representJavaBean(Set<Property> properties, Object javaBean) {
        if (!classTags.containsKey(javaBean.getClass())){
            addClassTag(javaBean.getClass(), Tag.MAP);
           }

        return super.representJavaBean(properties, javaBean);
    }
};



DumperOptions dumperOptions = new DumperOptions();
//prints the yaml as nested blocks
dumperOptions.setDefaultFlowStyle(DumperOptions.FlowStyle.BLOCK);
//indicatorIndent indents the '-' character for lists
dumperOptions.setIndicatorIndent(2);
//This is the workaround. Indent must be set to at least 2 higher than the indicator indent because of how whitespace is handled.
//If not set to 2 higher, then the newline is added.
dumperOptions.setIndent(4);
Yaml yaml = new Yaml(representer, dumperOptions);
//prints the object to a yaml string.
yaml.dump(object);

解决方法是在 DumperOptions 上设置缩进属性。您需要将缩进设置为至少比 indicatorIndent 高 2 的值，否则将添加换行符。这是由于在 snakeyaml 中处理空格的方式。

Answer 2

查看 Jackson 源代码，snakeyaml 转储程序选项的创建方式如下： @Andrey 你觉得这好看吗？

    protected DumperOptions buildDumperOptions(int jsonFeatures, int yamlFeatures,
            org.yaml.snakeyaml.DumperOptions.Version version)
    {
        DumperOptions opt = new DumperOptions();
        // would we want canonical?
        if (Feature.CANONICAL_OUTPUT.enabledIn(_formatFeatures)) {
            opt.setCanonical(true);
        } else {
            opt.setCanonical(false);
            // if not, MUST specify flow styles
            opt.setDefaultFlowStyle(FlowStyle.BLOCK);
        }
        // split-lines for text blocks?
        opt.setSplitLines(Feature.SPLIT_LINES.enabledIn(_formatFeatures));
        // array indentation?
        if (Feature.INDENT_ARRAYS.enabledIn(_formatFeatures)) {
            // But, wrt [dataformats-text#34]: need to set both to diff values to work around bug
            // (otherwise indentation level is "invisible". Note that this should NOT be necessary
            // but is needed up to at least SnakeYAML 1.18.
            // Also looks like all kinds of values do work, except for both being 2... weird.
            opt.setIndicatorIndent(1);
            opt.setIndent(2);
        }
        // 14-May-2018: [dataformats-text#84] allow use of platform linefeed
        if (Feature.USE_PLATFORM_LINE_BREAKS.enabledIn(_formatFeatures)) {
            opt.setLineBreak(DumperOptions.LineBreak.getPlatformLineBreak());
        }
        return opt;
    }

Answer 3

我运行对此感兴趣并最终写了这篇博客文章来描述我想出的解决方案。简而言之，我创建了 YAMLGenerator 和 YAMLFactory 的自定义子类，并用它来配置 Jackson 的 YAMLMapper。不“干净”，但不是很大且相当有效。让我任意设置DumperOptions

以下来源，但 also available in this gist。

警告 - 我在 Kotlin 中完成了这一切，但这是微不足道的代码，应该很容易 back-portable 到 Java:

val mapper: YAMLMapper = YAMLMapper(MyYAMLFactory()).apply {
  registerModule(KotlinModule())
  setSerializationInclusion(JsonInclude.Include.NON_EMPTY)
}


class MyYAMLGenerator(
  ctx: IOContext,
  jsonFeatures: Int,
  yamlFeatures: Int,
  codec: ObjectCodec,
  out: Writer,
  version: DumperOptions.Version?
): YAMLGenerator(ctx, jsonFeatures, yamlFeatures, codec, out, version) {
  override fun buildDumperOptions(
    jsonFeatures: Int,
    yamlFeatures: Int,
    version: DumperOptions.Version?
  ): DumperOptions {
    return super.buildDumperOptions(jsonFeatures, yamlFeatures, version).apply {
      //
      // NOTE: CONFIGURATION HAPPENS HERE!!
      //
      defaultScalarStyle = ScalarStyle.LITERAL;
      defaultFlowStyle = FlowStyle.BLOCK
      indicatorIndent = 2
      nonPrintableStyle = ESCAPE
      indent = 4
      isPrettyFlow = true
      width = 100
      this.version = version
    }
  }
}

class MyYAMLFactory(): YAMLFactory() {
  @Throws(IOException::class)
  override fun _createGenerator(out: Writer, ctxt: IOContext): YAMLGenerator {
    val feats = _yamlGeneratorFeatures
    return MyYAMLGenerator(ctxt, _generatorFeatures, feats,_objectCodec, out, _version)
  }
}

Answer 4

由于 YAMLGenerator.Feature.INDENT_ARRAYS_WITH_INDICATOR 的引入，在今天至少使用 jackson-dataformat-yaml 版本 2.12.x 的环境中，您可以简单地执行以下操作：

public ObjectMapper yamlObjectMapper() {
    final YAMLFactory factory = new YAMLFactory()
            .enable(YAMLGenerator.Feature.INDENT_ARRAYS_WITH_INDICATOR)
            .enable(YAMLGenerator.Feature.MINIMIZE_QUOTES)
            .disable(YAMLGenerator.Feature.WRITE_DOC_START_MARKER);

    return new ObjectMapper(factory);
}

这将为您提供以下输出：

employees:
 - name: John
   age: 26
 - name: Bill
   age: 17

Jackson YAML 序列化对象数组格式

Jackson YAML Serialization Object Arrays Format

java

serialization

yaml

snakeyaml

jackson