add:根据name（传入String）获取Identity；设置默认Identity（不带密码的）

src/main/java/security/KeyChain.java

@@ -98,6 +98,49 @@ public class KeyChain {
         }
     }
 
+    /**
+     * 设置默认的的网络身份，不带密码
+     * @param identity 身份对象
+     * @return boolean
+     * @author zhengqi wu
+     * @date 2021/6/12
+     **/
+    public void setDefaultIdentity(Identity identity) throws KeyChainException {
+        boolean res = false;
+        try {
+            res = this.identityManager.setDefaultIdentity(identity, true); // 操作修改到数据库中
+        }
+        catch (Exception e)
+        {
+            throw new KeyChainException("Set Default Identity Failed! " + e.getMessage());
+        }
+
+        if (!res)
+        {
+            throw new KeyChainException("Maybe the identity is null.");
+        }
+        this.currentIdentity = identity;
+    }
+
+    /**
+     * 以身份名称字符串名称获取身份对象，查询不到返回为空
+     * @param identityName 身份名称字符串
+     * @return Identity 身份对象
+     * @author zhengqi wu
+     * @date 2021/6/12
+     **/
+    public Identity getIdentityByName(String identityName) throws KeyChainException {
+        Identity res = null;
+        try {
+            res = this.identityManager.getIdentityByName(identityName);
+        }
+        catch (Exception e)
+        {
+            throw new KeyChainException("Get" + identityName + " failed! " + e.getMessage());
+        }
+        return res;
+    }
+
     /**
      * 为一个网络身份申请证书
      * @param identity