Sure, here's a Java program that converts a string into an InputStream:

import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;

public class StringToInputStreamConverter {
    public static void main(String[] args) {
        String str = "Hello, world!";
        
        InputStream inputStream = new ByteArrayInputStream(str.getBytes(StandardCharsets.UTF_8));
        
        // Do something with the input stream
        // ...
    }
}

In this program, we first create a string variable called str.

We then use the getBytes method of the String class to convert the string to a byte array, using the StandardCharsets.UTF_8 encoding. We create a new ByteArrayInputStream object with the byte array as input.

Finally, we have an InputStream object that we can use to read the data from the string. In this example, we simply create the input stream and don't do anything with it, but you can use it to read the data and process it as needed.

Note that the getBytes method can throw an UnsupportedEncodingException if the specified encoding is not supported, so you should handle this exception in your code if there's a possibility that the encoding might not be supported.