@NodeEntity
public class WebPage {
    @GraphId
    private Long nodeId;

    private String url;

    @Relationship(type = "LINKED_TO", direction = Relationship.OUTGOING)
    private Set<Link> outgoingLinks = new HashSet<>();

    public WebPage() {}

    public String getUrl() {
        return url;
    }

    public WebPage setUrl(String url) {
        this.url = url;
        return this;
    }

    @Relationship(type = "LINKED_TO", direction = Relationship.OUTGOING)
    public Set<Link> getOutgoingLinks() {
        return outgoingLinks;
    }

    @Relationship(type = "LINKED_TO", direction = Relationship.OUTGOING)
    public void setOutgoingLinks(Set<Link> outgoingLinks) {
        this.outgoingLinks = outgoingLinks;
    }


    public void addOutgoingLink(WebPage linkedWebPage, String anchor) {
        Link outgoingLink = new Link(this, linkedWebPage, anchor);
        outgoingLinks.remove(outgoingLink);
        outgoingLinks.add(outgoingLink);
    }
}

@RelationshipEntity(type = "LINKED_TO")
public class Link {
    @GraphId
    Long id;

    @StartNode
    private WebPage sourceWebPage;
    @EndNode
    private WebPage linkWebPage;

    @Property
    private String anchor;

    public Link() {}

    public Link(WebPage sourceWebPage, WebPage linkWebPage, String anchor) {
        this.sourceWebPage = sourceWebPage;
        this.linkWebPage = linkWebPage;
        this.anchor = anchor;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((linkWebPage == null) ? 0 : linkWebPage.hashCode());
        result = prime * result + ((sourceWebPage == null) ? 0 : sourceWebPage.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Link other = (Link) obj;
        if (linkWebPage == null) {
            if (other.linkWebPage != null)
                return false;
        } else if (!linkWebPage.equals(other.linkWebPage))
            return false;
        if (sourceWebPage == null) {
            if (other.sourceWebPage != null)
                return false;
        } else if (!sourceWebPage.equals(other.sourceWebPage))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "Link [sourceWebPage=" + sourceWebPage + ", linkWebPage=" + linkWebPage
                        + ", anchor=" + anchor + "]";
    }

}

@Repository
public interface WebPageRepository extends GraphRepository<WebPage>{
    WebPage findByUrl(@Param("url") String url);
}

@Test
public void test() {
    WebPage sourceWebPage = webPageRepository.findByUrl("http://www.test.com/");
    if (sourceWebPage == null) {
        sourceWebPage = new WebPage().setUrl("http://www.test.com/");
    }
    WebPage linkedWebPage = webPageRepository.findByUrl("http://www.example.com/");
    if (linkedWebPage == null) {
        linkedWebPage = new WebPage().setUrl("http://www.example.com/");
    }

    String anchor = "test";
    sourceWebPage.addOutgoingLink(linkedWebPage, anchor);
    webPageRepository.save(sourceWebPage);
}

public void addOutgoingLink(WebPage linkedWebPage, String anchor) {
    Link outgoingLink = new Link(this, linkedWebPage, anchor);
    outgoingLinks.remove(outgoingLink);
    outgoingLinks.add(outgoingLink);
}