fix read policy (#414)

Author: WeiXinChan

src/main/java/com/alipay/oceanbase/rpc/ObTableClient.java

@@ -2754,15 +2754,15 @@ public ObTableClientType getClientType(RunningMode runningMode) {
         }
     }
 
-    public void setReadConsistency(ObReadConsistency readConsistency) throws IllegalArgumentException {
+    public void setReadConsistency(ObReadConsistency readConsistency) {
         tableRoute.setReadConsistency(readConsistency);
     }
 
     public String getReadConsistency() {
         return tableRoute.getReadConsistency().name();
     }
 
-    public void setRoutePolicy(ObRoutePolicy policy) throws IllegalArgumentException {
+    public void setRoutePolicy(ObRoutePolicy policy) {
         tableRoute.setRoutePolicy(policy);
     }
 

src/main/java/com/alipay/oceanbase/rpc/location/model/TableRoute.java

@@ -158,7 +158,7 @@ public ObReadConsistency getReadConsistency() {
      * Set read consistency level.
      * @param readConsistency read consistency level
      */
-    public void setReadConsistency(ObReadConsistency readConsistency) throws IllegalArgumentException {
+    public void setReadConsistency(ObReadConsistency readConsistency) {
         this.consistencyLevel = readConsistency;
     }
 

src/main/java/com/alipay/oceanbase/rpc/location/model/partition/ObPartitionLocation.java

@@ -104,26 +104,38 @@ private ReplicaLocation getReadReplicaNoLdc(ObRoutePolicy routePolicy) {
 
     private ReplicaLocation getReadReplicaByRoutePolicy(ObRoutePolicy routePolicy)
                                                                                   throws IllegalArgumentException {
+        // 路由策略优先：FOLLOWER_FIRST 优先选择 follower，FOLLOWER_ONLY 只能选择 follower
+        // 在满足路由策略的前提下，按就近原则选择（同机房 -> 同 region -> 其他 region）
+
+        // 优先在同机房找 follower
         for (ReplicaLocation r : sameIdc) {
-            if (r.isValid()) {
+            if (r.isValid() && !r.isLeader()) {
                 return r;
             }
         }
+        
+        // 如果同机房没有 follower，在同 region 找 follower
         for (ReplicaLocation r : sameRegion) {
-            if (r.isValid()) {
+            if (r.isValid() && !r.isLeader()) {
                 return r;
             }
         }
+        
+        // 如果同 region 没有 follower，在其他 region 找 follower
         for (ReplicaLocation r : otherRegion) {
-            if (r.isValid()) {
+            if (r.isValid() && !r.isLeader()) {
                 return r;
             }
         }
-
+        
+        // 如果都没有找到 follower
         if (routePolicy == ObRoutePolicy.FOLLOWER_ONLY) {
+            // FOLLOWER_ONLY 必须选择 follower，没有就抛出异常
             throw new IllegalArgumentException("No follower replica found for route policy: "
-                                               + routePolicy);
+                                                + routePolicy);
         }
+
+        // 如果都没有找到，返回 leader（兜底）
         return leader;
     }