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。
private Exporter<T> exporter;
        public DestroyableExporter(Exporter<T> exporter) {
            this.exporter = exporter;
        }
        @Override
        public Invoker<T> getInvoker() {
            return exporter.getInvoker();
        }
        @Override
        public void unexport() {
            exporter.unexport();
        }
    }
    /**
     * Reexport: the exporter destroy problem in protocol
     * 1.Ensure that the exporter returned by registryprotocol can be normal destroyed
     * 2.No need to re-register to the registry after notify
     * 3.The invoker passed by the export method , would better to be the invoker of exporter
     */
    private class OverrideListener implements NotifyListener {