protected void renderShadowMap(int shadowMapIndex) {
        shadowMapOccluders = getOccludersToRender(shadowMapIndex, shadowMapOccluders);
        Camera shadowCam = getShadowCam(shadowMapIndex);

        //saving light view projection matrix for this split
        lightViewProjectionsMatrices[shadowMapIndex].set(shadowCam.getViewProjectionMatrix());
        renderManager.setCamera(shadowCam, false);

        renderManager.getRenderer().setFrameBuffer(shadowFB[shadowMapIndex]);
        renderManager.getRenderer().clearBuffers(true, true, true);
        renderManager.setForcedRenderState(forcedRenderState);

        // render shadow casters to shadow map and disables the lightfilter
        LightFilter tmpLightFilter = renderManager.getLightFilter();
        renderManager.setLightFilter(NULL_LIGHT_FILTER);
        viewPort.getQueue().renderShadowQueue(shadowMapOccluders, renderManager, shadowCam, true);
        renderManager.setLightFilter(tmpLightFilter);
        renderManager.setForcedRenderState(null);
    }
responsible for displaying the frustum of the shadow cam for debug
purpose

@param shadowMapIndex the index of the shadow map
jme3-core/src/main/java/com/jme3/shadow/AbstractShadowRenderer.java