Java8编译的WAR在Java6环境运行未抛major minor异常，是否正常？

Absolutely, this is a totally normal scenario—here's why:

• Your compiled bytecode is likely Java 6 compatible
  Even though you used Java 8 to compile the code, you probably configured your build tool (Ant, Maven, Gradle, etc.) to generate Java 6-compatible bytecode. For example, with Ant, you might have set the source and target attributes to 1.6 in the <javac> task. The Created-By entry in your manifest.mf only records which JDK was used for compilation—it doesn't dictate the actual bytecode version that the JRE executes.

• Tomcat 7.0.29 supports Java 6+
  Tomcat 7's minimum required JRE is Java 6, so it can happily load and run bytecode targeted at Java 6. The "unsupported major/minor version" error only pops up when the JRE encounters bytecode that was compiled for a newer Java version than it can handle.

• How to confirm this
  You can verify the actual bytecode version of your class files using the javap tool. Run this command on one of your compiled classes:

  javap -verbose YourClass | grep "major version"
  

  If the output shows major version: 50, that means the bytecode is Java 6 compatible (Java 6 = 50, Java 8 = 52). This is the real determinant of whether the JRE can run the code, not the manifest entry.

内容的提问来源于stack exchange，提问作者Soham Banerjee