The boundary effect on the diffusiophoresis of a colloidal particle is investigated theoretically by considering a soft spherical particle at an arbitrary position in a spherical cavity. The particle, which comprises a rigid core and an ion-penetrable layer, simulates biocolloids and particles covered by an artificial membrane layer. The diffusiophoretic behavior of the particle is governed by two types of DLP, the electrophoresis arising from the difference in the diffusivities of ionic species and diffusioosmotic flow. The influences of the thickness of the double layer, the size of the cavity, and the nature and the position of the particle on its diffusiophoretic behavior are discussed. We show that the presence of a boundary can have a profound influence on the behavior of a particle. The effect of electrophoresis can also lead to interesting diffusiophoretic behavior.