[Solved]-This server requires an execution environment of JavaSE-1.8, but no valid JRE was found. Caution is advised-eclipse

install an openjdk 11 jre and rather select that as the execution environment.

that is window -> preference -> java -> installed jre's

although chances are you've already got that one installed so just select it from the execution environment.

unless there's a good reason why you're wanting to use an alternate jre.

sorry for my bad english. to resolve it, go to

window -> preference -> java -> compiler

and change the value of compiler compliance level to 1.8 it work for me.