Jackson JSON反序列化:每行中的数组元素

Question

我正在使用杰克逊,并希望打印JSON,使得数组中的每个元素都会进入每一行,例如:

{
  "foo" : "bar",
  "blah" : [
    1,
    2,
    3
  ]
}

设置为SerializationFeature.INDENT_OUTPUTtrue只会为对象字段而不是数组元素插入换行符,而是以这种方式打印对象:

{
  "foo" : "bar",
  "blah" : [1, 2, 3]
}

有谁知道如何实现这一目标？谢谢!

Answer 1

感谢有用的提示,我能够ObjectMapper按如下方式配置所需的缩进:

private static class PrettyPrinter extends DefaultPrettyPrinter {
    public static final PrettyPrinter instance = new PrettyPrinter();

    public PrettyPrinter() {
        _arrayIndenter = Lf2SpacesIndenter.instance;
    }
}

private static class Factory extends JsonFactory {
    @Override
    protected JsonGenerator _createGenerator(Writer out, IOContext ctxt) throws IOException {
        return super._createGenerator(out, ctxt).setPrettyPrinter(PrettyPrinter.instance);
    }
}

{
    ObjectMapper mapper = new ObjectMapper(new Factory());
    mapper.configure(SerializationFeature.INDENT_OUTPUT, true);
}

Answer 2

您可以扩展DefaultPrettyPrinter并覆盖beforeArrayValues(...)和writeArrayValueSeparator(...)之前的方法以实现所需的行为.之后,您必须通过setPrettyPrinter(...)将新实现添加到JsonGenerator .

Answer 3

如果您不想扩展，DefaultPrettyPrinter也可以在indentArraysWith外部设置属性：

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.enable(SerializationFeature.INDENT_OUTPUT);

DefaultPrettyPrinter prettyPrinter = new DefaultPrettyPrinter();
prettyPrinter.indentArraysWith(DefaultPrettyPrinter.Lf2SpacesIndenter.instance);

String json = objectMapper.writer(prettyPrinter).writeValueAsString(object);

Answer 4

映射器可以配置（jackson-2.6）：

ObjectMapper mapper = ...
DefaultPrettyPrinter prettyPrinter = new DefaultPrettyPrinter();
prettyPrinter.indentArraysWith(DefaultIndenter.SYSTEM_LINEFEED_INSTANCE);
mapper.setDefaultPrettyPrinter(prettyPrinter);

//use mapper