使用 ObjectMapper类 必须引用3个jar包（jackson-databind，jackson-core，jackson-annotations）
缺少 jackson-core ，会报错 The type com.fasterxml.jackson.core.JsonParser cannot be resolved. It is indirectly referenced from required .class files
缺少 jackson-annotations ，会报错 Exception in thread "main" java.lang.NoClassDefFoundError: com/fasterxml/jackson/annotation/JsonAutoDetect