To get the response body from a ServletResponse object in Spring Boot, you can use the following method:

1. First, you will need to get the ServletResponse object as an instance of HttpServletResponse. You can do this by casting the ServletResponse object to HttpServletResponse.

HttpServletResponse httpResponse = (HttpServletResponse) servletResponse;

2. Next, you can use the getOutputStream() method of the HttpServletResponse object to get an instance of ServletOutputStream.

ServletOutputStream outputStream = httpResponse.getOutputStream();

3. You can then use the toByteArray() method of the ServletOutputStream to get the response body as a byte array.

byte[] responseBody = outputStream.toByteArray();

4. If you want to convert the response body to a string, you can use the new String(byte[]) constructor to create a string from the byte array.

String responseBodyString = new String(responseBody);