Use replaceAll() return value

The replaceAll() method returns the result. It does not modify the current string.

backend/src/main/java/io/metersphere/api/dto/definition/request/sampler/MsHTTPSamplerProxy.java

@@ -465,7 +465,7 @@ public class MsHTTPSamplerProxy extends MsTestElement {
                     url = "http://" + url;
                 }
                 if (StringUtils.isNotEmpty(this.getPort()) && this.getPort().startsWith("${")) {
-                    url.replaceAll(this.getPort(), "10990");
+                    url = url.replaceAll(this.getPort(), "10990");
                 }
                 if (url == null) {
                     MSException.throwException("请重新选择环境");