XStream XML Codec

build.gradle

project(":xstreamist") {
  dependencies {
    implementation 'com.thoughtworks.xstream:xstream:1.4.14'
    implementation 'com.fasterxml.woodstox:woodstox-core:6.2.3'
    implementation 'xpp3:xpp3:1.1.4c'
  }
}

MyXmlMessage.java

package xstreamist;

@XStreamAlias("my-msg")
public class MyXmlMessage {
    // ...
};

XStreamist.java

package xstreamist;

import com.thoughtworks.xstream.XStream;
import com.thoughtworks.xstream.converters.SingleValueConverter;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
import com.thoughtworks.xstream.io.xml.CompactWriter;
import com.thoughtworks.xstream.io.xml.Xpp3Driver;
import org.apache.commons.io.output.StringBuilderWriter;

import javax.annotation.Nullable;
import java.io.Reader;
import java.io.StringReader;
import java.io.Writer;
import java.time.Duration;
import java.time.Instant;

public class XmlCodec {
  private static final ThreadLocal<XStream> xStream = ThreadLocal.withInitial(XmlCodec::createXStream);
  
  private static XStream createXStream() {
    final XStream xs = new XStream(new Xpp3Driver() {
      @Override
      public HierarchicalStreamWriter createWriter(final Writer out) {
        return new CompactWriter(out, getNameCoder());
      }
    });

    setupDefaultSecurity(xs);
    xs.allowTypesByWildcard(new String[]{"com.mycompany.**"});

    // http://x-stream.github.io/graphs.html
    xs.setMode(XStream.NO_REFERENCES);

    xs.processAnnotations(MyXmlMessage.class);
    xs.processAnnotations(MyAnotherXmlMessage.class);

    return xs;
  }
  
  static XStream xStream() {
    return xStream.get();
  }

  public static Object decode(String str) {
    return xStream().fromXML(new StringReader(str));
  }

  public static String encode(Object obj) {
    final StringBuilderWriter w = new StringBuilderWriter(256);
    xStream().toXML(obj, w);
    return w.toString();
  }
  
  public static final class InstantConverter implements SingleValueConverter {
    @Override public @Nullable String toString(final Object obj) { return obj == null ? null : String.valueOf(((Instant)obj).toEpochMilli()); }
    @Override public @Nullable Object fromString(final String str) { return str == null || str.isEmpty() ? null : Instant.ofEpochMilli(Long.parseLong(str)); }
    @Override public boolean canConvert(final Class type) { return Instant.class == type; }
  }

  public static final class DurationConverter implements SingleValueConverter {
    @Override public @Nullable String toString(final Object obj) { return obj == null ? null : String.valueOf(((Duration)obj).toMillis()); }
    @Override public @Nullable Object fromString(final String str) { return str == null || str.isEmpty() ? null : Duration.ofMillis(Long.parseLong(str)); }
    @Override public boolean canConvert(final Class type) { return Duration.class == type; }
  }
}