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。
public int getPort() {
        return port;
    }
    public URL setPort(int port) {
        return new URL(protocol, username, password, host, port, path, getParameters());
    }
    public int getPort(int defaultPort) {
        return port <= 0 ? defaultPort : port;
    }
    public String getAddress() {
        return port <= 0 ? host : host + ":" + port;
    }
    public URL setAddress(String address) {
        int i = address.lastIndexOf(':');
        String host;
        int port = this.port;
        if (i >= 0) {
            host = address.substring(0, i);
            port = Integer.parseInt(address.substring(i + 1));
        } else {
            host = address;
        }
        return new URL(protocol, username, password, host, port, path, getParameters());
    }
    public String getBackupAddress() {
        return getBackupAddress(0);
    }
    public String getBackupAddress(int defaultPort) {
        StringBuilder address = new StringBuilder(appendDefaultPort(getAddress(), defaultPort));
        String[] backups = getParameter(Constants.BACKUP_KEY, new String[0]);