as far as i know, most compilers (not checked jdk8) will transform this iteration into something like this:

```java
for (String webjarId : webjarConfigs.keySet()) {
webjarConfigsString = (new StringBuilder(String.valueOf(webjarConfigsString))).append("// webjar config for ").append(webjarId).append("\n").toString();
webjarConfigsString = (new StringBuilder(String.valueOf(webjarConfigsString))).append(webjarConfigs.get(webjarId)).append("\n").toString();
}
```