try-with-resources fails but try works

Question

I'm trying to set up a service which listens to a RabbitMQ server and I've set up code using the RabbitMQ Sample code from Github, which includes the following try-with-resources block

try (Connection connection = factory.newConnection();
     Channel channel = connection.createChannel()) {
        // code here
}

When I use the same code and build and run this service using java -cp myJar.jar MyService, it just starts and ends immediately (and echo $? returns 0)

However, if I replace the block with the following, then it works fine with the same command, and I'm able to start a listener to a RabbitMQ instance

try {
     Connection connection = factory.newConnection();
     Channel channel = connection.createChannel());

     // code here
}

---

The same happens even when I create database connections

try (Connection connection = dataSource.getConnection()) {
    //code here
}

fails but

try {
    Connection connection = dataSource.getConnection();
    //code here
}  

works fine, and allows me to use the connection to make entries into the DB as well.

---

Why is this happening? I'm using OpenJDK 11.0.2 and this service is standalone, but the rest of the codebase is a JAX-RS driven Rest API if it helps.

Answer 1

当块退出时，try-with-resources构造关闭资源。基本的try块代码不会关闭任何内容。那是两者之间的区别。

当您使用try-与资源，你需要实际DO与资源的东西。

如果在要打开的资源需要“长期存在”的地方编写代码，则try-with-resources不是正确的构造（尽管通常，这意味着您正在编写的类本身应该是AutoClosable的）。