improve WallFilter

src/main/java/com/alibaba/druid/wall/WallConfig.java

@@ -51,6 +51,7 @@ public class WallConfig implements WallConfigMBean {
 
     private boolean             commentAllow               = false;
     private boolean             strictSyntaxCheck          = true;
+    private boolean             constArithmeticAllow       = false;
 
     private boolean             describeAllow              = false;
 
@@ -366,6 +367,14 @@ public class WallConfig implements WallConfigMBean {
         this.strictSyntaxCheck = strictSyntaxCheck;
     }
 
+    public boolean isConstArithmeticAllow() {
+        return constArithmeticAllow;
+    }
+
+    public void setConstArithmeticAllow(boolean constArithmeticAllow) {
+        this.constArithmeticAllow = constArithmeticAllow;
+    }
+
     public Set<String> getDenyFunctions() {
         return denyFunctions;
     }