For example, departments (equivalent to our undergraduate courses) can take the exam directly, but generally speaking, junior college students are not advised to take this route, because it takes at least four years to prepare for the exam and the time and money costs are a bit high. When they graduate, they will take out an undergraduate degree, which is not high enough for their junior college degree, so it is generally recommended to take an examination of Japanese universities (that is, graduate students).
For example, in a big college (equivalent to our graduate students), junior college students need to pass the "pre-examination", that is, submit materials to the school 1-2 months in advance before they want to register, and conduct a "qualification examination" to judge whether the students have the same level as undergraduates through the materials. Only those who pass the qualification examination can take the university exam like ordinary candidates.
Both of the above tests can be transferred through a language school that has studied in Japan for some time. Some language schools with exam counseling have these two kinds of exam counseling, such as Chiyoda Language Institute, Tokyo International Culture, ISI Language School and so on, and the quality is not bad.