add some construction methods for more convenient use (#132) Co-authored-by: chengxin05 <chengxin05@baidu.com>

diff --git a/hugegraph-common/src/main/java/org/apache/hugegraph/config/HugeConfig.java b/hugegraph-common/src/main/java/org/apache/hugegraph/config/HugeConfig.java
index b765369..c48219f 100644
--- a/hugegraph-common/src/main/java/org/apache/hugegraph/config/HugeConfig.java
+++ b/hugegraph-common/src/main/java/org/apache/hugegraph/config/HugeConfig.java

@@ -55,6 +55,17 @@
         this.configPath = configFile;
     }
 
+    public HugeConfig(Map<String, Object> propertyMap) {
+        if (propertyMap == null) {
+            throw new ConfigException("The property map is null");
+        }
+
+        for (Map.Entry<String, Object> kv : propertyMap.entrySet()) {
+            this.addProperty(kv.getKey(), kv.getValue());
+        }
+        this.checkRequiredOptions();
+    }
+
     private void loadConfig(Configuration config) {
         if (config == null) {
             throw new ConfigException("The config object is null");

diff --git a/hugegraph-common/src/main/java/org/apache/hugegraph/event/EventHub.java b/hugegraph-common/src/main/java/org/apache/hugegraph/event/EventHub.java
index 0886e7e..5107fba 100644
--- a/hugegraph-common/src/main/java/org/apache/hugegraph/event/EventHub.java
+++ b/hugegraph-common/src/main/java/org/apache/hugegraph/event/EventHub.java

@@ -57,11 +57,14 @@
     }
 
     public EventHub(String name) {
-        LOG.debug("Create new EventHub: {}", name);
+        this(name, 1);
+    }
 
+    public EventHub(String name, int threadSize) {
+        LOG.debug("Create new EventHub {}", name);
         this.name = name;
         this.listeners = new ConcurrentHashMap<>();
-        EventHub.init(1);
+        EventHub.init(threadSize);
     }
 
     public static synchronized void init(int poolSize) {

diff --git a/hugegraph-common/src/main/java/org/apache/hugegraph/rest/RestResult.java b/hugegraph-common/src/main/java/org/apache/hugegraph/rest/RestResult.java
index 813aeff..82b7f39 100644
--- a/hugegraph-common/src/main/java/org/apache/hugegraph/rest/RestResult.java
+++ b/hugegraph-common/src/main/java/org/apache/hugegraph/rest/RestResult.java

@@ -38,9 +38,15 @@
     private final String content;
 
     public RestResult(Response response) {
-        this.status = response.getStatus();
-        this.headers = response.getHeaders();
-        this.content = response.readEntity(String.class);
+        this(response.getStatus(), response.readEntity(String.class),
+             response.getHeaders());
+    }
+
+    public RestResult(int status, String content,
+                      MultivaluedMap<String, Object> headers) {
+        this.status = status;
+        this.headers = headers;
+        this.content = content;
     }
 
     public int status() {