使用Java MongoDB 4.0.4 驱动使用Block<Document> 打印collection 时编译报错

Question

使用 Java MongoDB Driver 4.0.4, OpenJDK 11 and following the example on MongoDB docs 时，使用 findIterable.forEach(printBlock);

时出现编译错误

看起来 com.mongodb.Block http://mongodb.github.io/mongo-java-driver/4.0/driver/tutorials/aggregation/ 也没有被弃用。

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());
  }
};

错误：

[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>

Answer 1

文档显然已经过时了。如果您查看 FindIterable 的 javadoc (http://mongodb.github.io/mongo-java-driver/4.0/apidocs/mongodb-driver-sync/com/mongodb/client/FindIterable.html) 你会看到 forEach 是从 java.lang.Iterable 继承而来的，它采用 Consumer 作为参数，而不是 Block.

因此，将您的 printBlock 声明替换为：

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

...一切都会好起来的。

Answer 2

在 mtj 和 Mongodb 支持的帮助下，添加工作代码块..

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((Consumer<Document>)  d -> System.out.println( d.toJson())); 
}

或

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

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);
}

或参考https://jira.mongodb.org/browse/DOCS-13638

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);
}

Consumer<Document> printBlock = new Consumer<Document>() {
  public void accept(final Document doc) {
    System.out.println(doc.toJson());
  };
};

使用Java MongoDB 4.0.4 驱动使用Block<Document> 打印collection 时编译报错

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

java

mongodb

mongodb-java