URDF model not appearing in Rviz nor Gazebo

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i have been trying to open in gazebo and rviz a URDF file of a double pendulum that i have designed in solidworks and exported the URDF code using the URDF exporter. i am facing problems in visualizing my project in gazebo and rviz. The environments appear to be empty although the panels on the left indicate that all the link exist along with their properties. i can conclude from the position and orientation of the coordinate frames of each link that the scale of the robot is very small and in rviz a message appears indicating that the links have NO geometry.

Kindly check the URDF code below:

    <?xml version="1.0" encoding="utf-8"?>
<!-- This URDF was automatically created by SolidWorks to URDF Exporter! Originally created by Stephen Brawner (brawner@gmail.com) 
     Commit Version: 1.5.1-0-g916b5db  Build Version: 1.5.7152.31018
     For more information, please see http://wiki.ros.org/sw_urdf_exporter -->
<robot
  name="base_2links">
  <link
    name="base_link">
    <inertial>
      <origin
        xyz="-0.016 0.0034506 0.074794"
        rpy="0 0 0" />
      <mass
        value="0.027215" />
      <inertia
        ixx="2.0815E-06"
        ixy="3.1439E-22"
        ixz="-2.2393E-22"
        iyy="1.2394E-05"
        iyz="-1.2756E-22"
        izz="1.2544E-05" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://base_2links/meshes/base_link.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="0.79216 0.81961 0.93333 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://base_2links/meshes/base_link.STL" />
      </geometry>
    </collision>
  </link>
  <link
    name="link1">
    <inertial>
      <origin
        xyz="-0.00035493 0.020275 -0.012885"
        rpy="0 0 0" />
      <mass
        value="0.014265" />
      <inertia
        ixx="4.1101E-06"
        ixy="5.9474E-08"
        ixz="1.4157E-23"
        iyy="7.1379E-07"
        iyz="-1.3929E-23"
        izz="4.2611E-06" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://base_2links/meshes/link1.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="0.75294 0.75294 0.75294 1" />
      </material>
    </visual>
    <collision>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://base_2links/meshes/link1.STL" />
      </geometry>
    </collision>
  </link>
  <joint
    name="joint1"
    type="continuous">
    <origin
      xyz="-0.016 -0.062794 0.013249"
      rpy="1.5708 0.017504 -3.1416" />
    <parent
      link="base_link" />
    <child
      link="link1" />
    <axis
      xyz="0 0 1" />
  </joint>
  <link
    name="link2">
    <inertial>
      <origin
        xyz="0.014984 0.013663 -0.0038295"
        rpy="0 0 0" />
      <mass
        value="0.014265" />
      <inertia
        ixx="2.2556E-06"
        ixy="-1.692E-06"
        ixz="4.6898E-22"
        iyy="2.5683E-06"
        iyz="5.9919E-22"
        izz="4.2611E-06" />
    </inertial>
    <visual>
      <origin
        xyz="0 0 0"
        rpy="0 0 0" />
      <geometry>
        <mesh
          filename="package://base_2links/meshes/link2.STL" />
      </geometry>
      <material
        name="">
        <color
          rgba="0.75294 0.75294 0.75294 1" /> ...