putMessage：采用wrap(ByteBuffer, int offset, int length)进行存储，并记录更新偏移位置offset
getMessage :采用get(ByteBuffer, int offset, int length)进行定向读取缓存数据。
Brief changelog
add a java class
Verifying this change
Follow this checklist to help us incorporate your contribution quickly and easily. Notice, it would be helpful if you could finish the following 5 checklist(the last one is not necessary)before request the community to review your PR.
[x] Make sure there is a Github issue filed for the change (usually before you start working on it). Trivial changes like typos do not require a Github issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
[x] Format the pull request title like [ISSUE #123] Fix UnknownException when host config not exist. Each commit in the pull request should have a meaningful subject line and body.
[x] Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
[x] Write necessary unit-test(over 80% coverage) to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add integration-test in test module.
[x] Run mvn -B clean apache-rat:check findbugs:findbugs checkstyle:checkstyle to make sure basic checks pass. Run mvn clean install -DskipITs to make sure unit-test pass. Run mvn clean test-compile failsafe:integration-test to make sure integration-test pass.
ISSUE https://github.com/rocketmq-baiji/rocketmq/issues/1
What is the purpose of the change
实现一个非持久化的broker
思路
考虑队列堆积等情况，我们采用堆外内存.
Brief changelog
add a java class
Verifying this change
Follow this checklist to help us incorporate your contribution quickly and easily. Notice,
it would be helpful if you could finish the following 5 checklist(the last one is not necessary)before request the community to review your PR.[ISSUE #123] Fix UnknownException when host config not exist. Each commit in the pull request should have a meaningful subject line and body.mvn -B clean apache-rat:check findbugs:findbugs checkstyle:checkstyleto make sure basic checks pass. Runmvn clean install -DskipITsto make sure unit-test pass. Runmvn clean test-compile failsafe:integration-testto make sure integration-test pass.