China on Friday appointed a naval commander with experience in the South China Sea as its minister of defense, filling a monthslong vacancy created by the unexplained disappearance of the previous minister, who appeared to have fallen in an investigation into possible corruption or other misdeeds. The appointment of the commander, Adm. Dong Jun, as defense minister was finalized by China’s Communist Party leader, Xi Jinping, after formal approval by lawmakers, the Xinhua news agency reported. Speculation spread earlier in the week that Admiral Dong would be named to that…