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Lightweight FOLIO module development library for Vert.x that supports OpenAPI


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Copyright (C) 2021-2023 The Open Library Foundation

This software is distributed under the terms of the Apache License, Version 2.0. See the file "LICENSE" for more information.


folio-vertx-lib is a library for developing FOLIO modules based on Vert.x. This is a library, not a framework, with utilities such as:

  • OpenAPI support
  • Tenant API 2.0 support
  • PostgreSQL utilities
  • CQL support

Main Verticle

The Vert.x OpenAPI unlike many OpenAPI implementations does not generate any code for you. Everything happens at run-time. Only requests are validated, not responses.

Place your OpenAPI specification and auxiliary files somewhere in resources, such as resources/openapi.

In the following example, we will use OpenAPI spec books-1.0.yaml. The code snippets shown are from: MainVerticle , BookService and BookStorage.

Unlike RMB, you define MainVerticle yourself - no fancy initializers - you decide.


public class MainVerticle extends AbstractVerticle {
  public void start(Promise<Void> promise) {
    TenantPgPool.setModule("mod-mymodule"); // PostgreSQL - schema separation

    final int port = Integer.parseInt( // listening port
        Config.getSysConf("http.port", "port", "8081", config()));

    MyApi myApi = new MyApi(); // your API, construct the way you like
    // routes for your stuff, tenant API and health
    RouterCreator [] routerCreators = {
        new Tenant2Api(myApi),
        new HealthApi(),
    HttpServerOptions so = new HttpServerOptions()
    // combine all routes and start server
    RouterCreator.mountAll(vertx, routerCreators, "mod-mymodule")
        .compose(router ->

Your API

Your API must implement RouterCreator and, optionally, TenantInitHooks if your implementation has storage and that storage must be prepared for a tenant.

With the API there is a corresponding OpenAPI specification.

The RouterCreator interface has just one method createRouter where you return a Router for your implementation. Normally that's created for you by the OpenAPI library, but you can also define it yourself.

For an OpenAPI based implementation it could look as follows:

public MyApi implements RouterCreator, TenantInitHooks {
  public Future<Router> createRouter(Vertx vertx) {
    return RouterBuilder.create(vertx, "openapi/myapi-1.0.yaml")
        .map(routerBuilder -> {
          handlers(vertx, routerBuilder);
          return routerBuilder.createRouter();

  private void handlers(Vertx vertx, RouterBuilder routerBuilder) {
        .operation("postTitles") // operationId in spec
        .handler(ctx -> {
          // doesn't do anything at the moment!
        .handler(ctx -> getTitles(vertx, ctx)
            .onFailure(cause -> {

To support tenant init, your module should implement preInit and postInit.

These methods takes tenant ID and tenant attributes object.

The preInit job should be "fast" and is a way for the module to check if the operation can be started.. ("pre-check"). The postInit should perform the actual migration.

The Tenant2Api implementation deals with purge (removes schema with cascade). Your implementation should only consider upgrade/downgrade. On purge, preInit is called, but postInit is not.


The PostgreSQL support is minimal. There's just enough to perform tenant separation and most environment variables that are also recognized by RMB such as DB_HOST, DB_PORT, DB_USERNAME, DB_PASSWORD, DB_DATABASE, DB_MAXPOOLSIZE, DB_SERVER_PEM.

The class TenantPgPool is a small extension to the PgPool interface. The key method is TenantPgPool.pool for constructing a pool for the current tenant. From that point, rest is plain Vert.x pg client. However, the schema should be used when referring to tables, etc. Use the getSchema method for that.

The TenantPgPool.setModule must be called before first use as is done in MainVerticle example earlier.

To illustrate these things, consider a module that prepares a table in tenant init.

  public Future<Void> postInit(Vertx vertx, String tenant, JsonObject tenantAttributes) {
    if (!tenantAttributes.containsKey("module_to")) {
      return Future.succeededFuture(); // doing nothing for disable
    TenantPgPool pool = TenantPgPool.pool(vertx, tenant);
    return pool.query(
            "CREATE TABLE IF NOT EXISTS " + pool.getSchema() + ".mytable "
                + "(id UUID PRIMARY key, title text)")


For CQL support all fields recognized must be explicitly defined. Undefined CQL fields are rejected.

Example definition:

    PgCqlDefinition pgCqlDefinition = PgCqlDefinition.create();
    pgCqlDefinition.addField("cql.allRecords", new PgCqlFieldAlwaysMatches());
    pgCqlDefinition.addField("id", new PgCqlFieldUuid());
    pgCqlDefinition.addField("title", new PgCqlFieldText().withFullText());

This definition can then be used in a handler to get books:

 private Future<Void> getBooks(Vertx vertx, RoutingContext ctx) {
    RequestParameters params = ctx.get(ValidationHandler.REQUEST_CONTEXT_KEY);
    String tenant = params.headerParameter(XOkapiHeaders.TENANT).getString();
    RequestParameter query = params.queryParameter("query");
    PgCqlQuery pgCqlQuery = pgCqlDefinition.parse(query == null ? null : query.getString());

    TenantPgPool pool = TenantPgPool.pool(vertx, tenant);
    String sql = "SELECT * FROM " + pool.getSchema() + ".mytable";
    String where = pgCqlQuery.getWhereClause();
    if (where != null) {
      sql = sql + " WHERE " + where;
    String orderBy = pgCqlQuery.getOrderByClause();
    if (orderBy != null) {
      sql = sql + " ORDER BY " + orderBy;
    return pool.query(sql).execute().onSuccess(rows -> {
      RowIterator<Row> iterator = rows.iterator();
      JsonArray books = new JsonArray();
      while (iterator.hasNext()) {
        Row row =;
        books.add(new JsonObject()
            .put("id", row.getUUID("id").toString())
            .put("title", row.getString("title"))
      ctx.response().putHeader("Content-Type", "application/json");
      JsonObject result = new JsonObject().put("books", books);

CQL queries of the form FIELD="" have a special meaning; they find all records where the named field is NOT NULL. (This behaviour is the same as in the old RAML Module Builder.) To search for records where the field is present but empty, the double-equal operator can be used: FIELD=="".

Additional information

Issue tracker

See project VERTXLIB at the FOLIO issue tracker.

Code of Conduct

Refer to the Wiki FOLIO Code of Conduct.

API documentation

API descriptions:

Generated API documentation.

Code analysis

SonarQube analysis

Download and configuration

The built artifacts for this module are available. See configuration for repository access.