我是否应该使用复合主键?

There seems to only be 2nd class support for composite database keys in Java's JPA (via EmbeddedId or IdClass annotations). And when I read up on composite keys, regardless of language, people keep coming across as them being a bad thing. But I cannot understand why. Are composite keys still acceptable to use these days? If not, why not?There seems to only be 2nd class support for co