# Sending Data to the Liberator

Let’s take a look at an example of how a client application can use StreamLink to modify data on a Liberator server. In this case the application creates a new record data item. This pattern is used for issuing all StreamLink commands.

## 1. Get an instance of the StreamLink class

The application will issue a subscription request to StreamLink, so the first thing to do is implement a `SubscriptionListener` that receives the updates resulting from the subscription. In the pseudo code fragments below the record subscription listener implementation is called `MySubscriptionListener`. So, let’s get an instance of the StreamLink class using:

```java
StreamLink streamLink = StreamLinkFactory.create({
                           liberator_urls: "rttp://liberator1:8080",
                           username: "demouser",
                           password: "demopass"
                           });
```

In StreamLink, there are variants of the constructor that enable you to obtain configuration from a properties file. The `create()` method also lets you set less common configuration options by passing in an optional `StreamLinkConfiguration` object.

## 2. Set up the command listener

Next, we set up the command listener using:

```java
// Create an instance of a class that implements CommandListener.
myCommandListener = new MyCommandListener();
```

## 3. Create the fields

Create the fields that you want to publish. In JavaScript, you can represent these in object literal notation:

```java
fields = {"dBestBid": "1.2345", "dBestAsk": "1.2466"};
```

## 4. Command StreamLink to send the fields

Issue a "Publish To Subject" command to streamLink to send the fields. Assuming the application is already connected to the Liberator, StreamLink sends the command immediately:

```java
streamLink.publishToSubject("/MyRecord", fields, myCommandListener);
```

When the command has executed successfully, StreamLink calls the `onCommandOk()` method of `myCommandListener` (instantiation of `MyCommandListener`). If the command fails, for example because the user does not have permission to create record subjects on Liberator, StreamLink calls `onCommandError()` instead.