HttpUtility。UrlEncode意外输出

您应该只编码查询字符串的值,而不是整个URI:

var uri = "http://jira-test.myServer.de/rest/api/2/search?jql=" +
          HttpUtility.UrlEncode("labels = \"F&E\"");

// Result: http://jira-test.myServer.de/rest/api/2/search?jql=labels+%3d+%22F%26E%22

正确的构造方法:

// Construct query string using HttpValueCollection, which handles escaping:
var queryString = HttpUtility.ParseQueryString(string.Empty);
queryString.Add("jql", "labels = \"F&E\"");

// Combine base URI with query string through UriBuilder:
var uriBuilder = new UriBuilder("http://jira-test.myServer.de/rest/api/2/search");
uriBuilder.Query = queryString.ToString();

// Get string representation:
string uri = uriBuilder.ToString();

// Result: http://jira-test.myserver.de:80/rest/api/2/search?jql=labels+%3d+%22F%26E%22