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javamongodbmongodb-java

Compile error when using Block<Document> to print collection using Java MongoDB 4.0.4 driver

When using Java MongoDB Driver 4.0.4, OpenJDK 11 and following the example on MongoDB docs, seeing a compile error when using findIterable.forEach(printBlock);

Also looks like com.mongodb.Block http://mongodb.github.io/mongo-java-driver/4.0/driver/tutorials/aggregation/ is not deprecated.

public String testLocal() {
  MongoClient mongoClient = MongoClients.create("mongodb://localhost:27017");
  MongoDatabase database = mongoClient.getDatabase("cord");
  MongoCollection<Document> collection1 = database.getCollection("papers");

  FindIterable<Document> findIterable = collection1.find(new Document());
  findIterable.forEach(printBlock);

}

public Block<Document> printBlock = new Block<Document>() {
  @Override
  public void apply(final Document document) {
    System.out.println(document.toJson());
  }
};

Error:

[ERROR] /Projects/cord/src/main/java/com/engg/java/cord/services/PrimaryService_Local.java:
[24,30] incompatible types: com.mongodb.Block<org.bson.Document> cannot be converted
 to java.util.function.Consumer<? super org.bson.Document>
Solution

  • The documentation obviously is outdated. If you look at the javadocs for FindIterable (http://mongodb.github.io/mongo-java-driver/4.0/apidocs/mongodb-driver-sync/com/mongodb/client/FindIterable.html) you'll see that forEach is inherited from java.lang.Iterable which takes a Consumer as a parameter, not a Block.

    Thus, replace your printBlock declaration with:

    public Consumer<Document> printBlock = document -> System.out.println(document.toJson());

    ... and all shall be fine.