Working on fetchers

Fetchers are the implementation of the search using online services. Some fetchers require API keys to get them working. To get the fetchers running in a JabRef development setup, the keys need to be placed in the respective environment variable. The following table lists the respective fetchers, where to get the key from and the environment variable where the key has to be placed.


Key Source

Environment Variable

Rate Limit


IEEE Xplore API portal


200 calls/day




Depending on the current network

SAO/NASA Astrophysics Data System



5000 calls/day

Springer Nature

Springer Nature API Portal


5000 calls/day

Zentralblatt Math



Depending on the current network

"Depending on the current network" means that it depends whether your request is routed through a network having paid access. For instance, some universities have subscriptions to MathSciNet.

On Windows, you have to log-off and log-on to let IntelliJ know about the environment variable change. Execute the gradle task "processResources" in the group "others" within IntelliJ to ensure the values have been correctly written. Now, the fetcher tests should run without issues.

Fulltext Fetchers

  • all fulltext fetchers run in parallel

  • the result with the highest priority wins

  • InterruptedException | ExecutionException | CancellationException are ignored

Trust Levels

  • SOURCE (highest): definitive URL for a particular paper

  • PUBLISHER: any publisher library

  • PREPRINT: any preprint library that might include non final publications of a paper

  • META_SEARCH: meta search engines

  • UNKNOWN (lowest): anything else not fitting the above categories

Current trust levels

All fetchers are contained in the package org.jabref.logic.importer.fetcher. Here we list the trust levels of some of them:

  • DOI: SOURCE, as the DOI is always forwarded to the correct publisher page for the paper

  • ScienceDirect: Publisher

  • Springer: Publisher

  • ACS: Publisher

  • IEEE: Publisher

  • Google Scholar: META_SEARCH, because it is a search engine

  • Arxiv: PREPRINT, because preprints are published there

  • OpenAccessDOI: META_SEARCH


  • A DOI uniquely identifies a paper. Per definition, a DOI leads to the right paper. Everything else is good guessing.

  • We assume the DOI resolution surely points to the correct paper and that publisher fetches may have errors: For instance, a title of a paper may lead to different publications of it. One the conference version, the other the journal version. --> the PDF could be chosen randomly

Code was first introduced at PR#3882.

Background on embedding the keys in JabRef

The keys are placed into the file.


In build.gradle, these variables are filled:

"springerNatureAPIKey": System.getenv('SpringerNatureAPIKey')

The BuildInfo class reads from that file.

new BuildInfo().springerNatureAPIKey

When executing ./gradlew run, gradle executes processResources and populates build/ accordingly. However, when working directly in the IDE, Eclipse keeps reading from src/main/resources. In IntelliJ, the task JabRef Main is executing ./gradlew processResources before running JabRef from the IDE to ensure the is properly populated.