2.7.0版本getContextPath方法：
```
protected String getContextPath(URL url) {
        String contextPath = url.getPath();
        return contextPath.endsWith("/") ? contextPath.substring(0,contextPath.length()-1) : contextPath;
    }
```
无法将方法置入web容器中，退回2.6.5版本的方法：
```
protected String getContextPath(URL url) {
        int pos = url.getPath().lastIndexOf("/");
        return pos > 0 ? url.getPath().substring(0, pos) : "";
    }
```
使用正常，两个方法应该不等价的。
}
            protocol = url.substring(0, i);
            url = url.substring(i + 3);
        } else {
            
            i = url.indexOf(":/");
            if (i >= 0) {
                if (i == 0) {
                    throw new IllegalStateException("url missing protocol: \"" + url + "\"");
                }
                protocol = url.substring(0, i);
                url = url.substring(i + 1);
            }
        }
        i = url.indexOf("/");
        if (i >= 0) {
            path = url.substring(i + 1);
            url = url.substring(0, i);
        }
        i = url.lastIndexOf("@");
        if (i >= 0) {
            username = url.substring(0, i);
            int j = username.indexOf(":");
            if (j >= 0) {
                password = username.substring(j + 1);
                username = username.substring(0, j);
            }
            url = url.substring(i + 1);
        }
        i = url.lastIndexOf(":");