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§Java Configuration API Migration

The class play.Configuration was deprecated in favor of using Typesafe Config directly. So, instead of using play.Configuration you must now use com.typesafe.config.Config. For example:

Before:

import play.Configuration;
public class Foo {
    private final Configuration configuration;

    @javax.inject.Inject
    public Foo(Configuration configuration) {
        this.configuration = configuration;
    }
}

After:

import com.typesafe.config.Config;

public class Foo {
    private final Config config;

    @javax.inject.Inject
    public Foo(Config config) {
        this.config = config;
    }
}

§Config values should always be defined

The main difference between the Config and play.Configuration APIs is how to handle default values. Typesafe Config advocates that all configuration keys must be declared in your .conf files, including the default values.

Play itself is using reference.conf files to declare default values for all the possible configurations. To avoid the hassle of handling missing values, you can do the same if you are distributing a library. When the configuration is read, the application.conf files are layered on top of the reference.conf configuration. For example:

Before (configuration is play.Configuration):

// Here we have the default values inside the code, which is not the idiomatic way when using Typesafe Config.
Long timeout = configuration.getMilliseconds("my.service.timeout", 5000); // 5 seconds

After:

# This is declared in `conf/reference.conf`.
my.service.timeout = 5 seconds

And you can eventually override the value in your application.conf file:

# This will override the value declared in reference.conf
my.service.timeout = 10 seconds

This is especially useful when creating modules, since your module can provide reference values that are easy to override. Your Java code will then look like:

Long timeout = config.getDuration("my.service.timeout", TimeUnit.MILLISECONDS);

where config is your com.typesafe.config.Config instance.

§Manually checking values

If you don’t want or if you cannot have default values for some reason, you can use Config.hasPath or Config.hasPathOrNull to check if the value is configured before accessing it. This is a better option if the configuration is required but you can’t provide a reference (default) value:

import com.typesafe.config.Config;
import com.typesafe.config.ConfigException;

public class EmailServerConfig {

    private static final String SERVER_ADDRESS_KEY = "my.smtp.server.address";

    private final Config config;

    @javax.inject.Inject
    public EmailServerConfig(Config config) {
        this.config = config;
    }

    // The relevant code is here. First use `hasPath` to check if the configuration
    // exists and, if not, throw an exception.
    public String getSmtpAddress() {
        if (config.hasPath(SERVER_ADDRESS_KEY)) {
            return config.getString(SERVER_ADDRESS_KEY);
        } else {
            throw new ConfigException.Missing(SERVER_ADDRESS_KEY);
        }
    }
}

Next: Play 2.5