如何在自定义log4j2 jsonlayout插件中查找线程上下文

Question

我已经实现了以下插件来为log4j日志创建自定义Json布局。我不确定如何在插件中实现上下文查找。例如，应用程序将某些密钥放在MDC中，并在log4j.xml中使用以下配置，必须将其写入日志中。

<KeyValuePair key="customerId" value="$${customerId}" />. 

插件

@Plugin(name = "CustomJsonLayout", category = "Core", elementType = "layout", printObject = true)
public class CustomJsonLayout extends AbstractStringLayout {
private final ObjectMapper objectMapper;

CustomJsonLayout(Charset charset) {
    super(charset);
    SimpleModule module = new SimpleModule();
    module.addSerializer(LogEvent.class, new LogEventSerializer());
    module.addSerializer(ReadOnlyStringMap.class, new ContextDataSerializer() {
    });
    objectMapper = new ObjectMapper();
    objectMapper.registerModule(module);
    objectMapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY);
}

@Override
public String toSerializable(LogEvent logEvent) {
    try {
        return objectMapper.writeValueAsString(logEvent);
    } catch (JsonProcessingException e) {
        throw new IllegalStateException(e);
    }
}

private static class LogEventSerializer extends StdSerializer<LogEvent> {
    LogEventSerializer() {
        super(LogEvent.class);
    }

    @Override
    public void serialize(LogEvent value, JsonGenerator gen, SerializerProvider provider) throws IOException {
        String pattern = "yyyy-MM-dd HH:mm:ss.SSS";
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(pattern);
        String date = simpleDateFormat.format(new Date(value.getTimeMillis()));

        gen.writeStartObject();
        gen.writeStringField("timestamp", date);
        gen.writeStringField("component", MicroService.getAppName());
        gen.writeStringField("severity", value.getLevel().name());
        gen.writeObjectField("msg", value.getMessage().getFormattedMessage());
        gen.writeEndObject();
        gen.writeRaw("\n");
    }
}

@PluginBuilderFactory
public static <B extends Builder<B>> B newBuilder() {
    return new Builder<B>().asBuilder();
}

public static class Builder<B extends Builder<B>> extends org.apache.logging.log4j.core.layout.AbstractStringLayout.Builder<B> implements org.apache.logging.log4j.core.util.Builder<CustomJsonLayout> {
    Builder() {
        this.setCharset(StandardCharsets.UTF_8);
    }

    public CustomJsonLayout build() {
        return new CustomJsonLayout(this.getCharset());
    }
}
}