Java CPU and PSU Releases Explained

Starting with the release of Java SE 7 Update 71 (Java SE 7u71) in October 2014, Oracle will release a Critical Patch Update (CPU) at the same time as a corresponding Patch Set Update (PSU) for Java SE 7.

自从Java SE 7u71在2014年10月发行后，Oracle会在发行Java SE 7的PSU版的同时发布对应的核心补丁更新（CPU）版。

1. 什么是PSU/CPU？
CPU: Critical Patch Update
Oracle对于其产品每个季度发行一次的安全补丁包，通常是为了修复产品中的安全隐患。
PSU: Patch Set Updates
Oracle对于其产品每个季度发行一次的补丁包，包含了bug的修复。Oracle选取被用户下载数量多的，并且被验证过具有较低风险的补丁放入到每个季度的PSU中。在每个PSU中不但包含Bug的修复而且还包含了最新的CPU。

可以将CPU版（奇数版）理解为稳定版，PSU版（偶数版）理解为尝鲜版。

Which Java version should I choose: the CPU or the PSU?

Oracle strongly recommends that all Java SE users upgrade to the latest CPU release available for a release family. Most users should choose the CPU release.
Users should only use the corresponding PSU release if they are being impacted by one of the additional bugs fixed in that version as noted in the release notes.

The subsequent CPU release will contain all of the fixes from the current PSU. For this reason, organizations should test the current PSU in their environment in anticipation of these fixes being included in the next CPU.

What is the difference between a Java CPU and PSU release?

Java SE Critical Patch Updates (CPU) contain fixes to security vulnerabilities and critical bug fixes. Oracle strongly recommends that all Java SE users upgrade to the latest CPU releases as they are made available. Java SE CPU releases are odd numbered versions (i.e. 7u71, 7u65 – see more on Java SE version numbering schemes here).

Java SE Patch Set Updates (PSU) contain all of fixes in the corresponding CPU, as well as additional non-critical fixes. Java PSU releases should only be used if you are being impacted by one of the additional bugs fixed in that version. The release notes call out the additional fixes available in Java SE PSU releases.

Is the cadence of CPU releases changing?

As before, Java SE CPU releases are scheduled for release on the Tuesday closest to the 17th day of January, April, July and October under the normal Oracle Critical Patch Update schedule.

Starting in October 2014 with the release of Java SE 7u71 (CPU) and Java SE 7u72 (PSU), Oracle plans to additionally release a corresponding PSU release along with each CPU release for Java SE 7. PSU releases provide organizations and developers with access to non-critical fixes in addition to the critical fixes contained in the corresponding CPU.

总结，如同网上说：

奇数版本为BUG修正并全部通过检验的版本，官方强烈推荐使用这个版本。

偶数版本包含了奇数版本所有的内容，以及未被验证的BUG修复，Oracle官方表示：除非你深受BUG困扰，否则不推荐您使用这个版本。