Ubuntu16.04安裝Jdk1.8和Tomcat8問題處理

Ubuntu16.04上原本安裝有jdk1.7版本，現在打算安裝一個1.8版本，並安裝Tomcat8，但是安裝以後發現啟動Tomcat時，始終報錯：

org.apache.catalina.startup.VersionLoggerListener.log Server version:        Apache Tomcat/8.0.32 (Ubuntu)
org.apache.catalina.startup.VersionLoggerListener.log Server built:          May 28 2018
 
 17:21:29 UTC
org.apache.catalina.startup.VersionLoggerListener.log Server number:         8.0.32.0
org.apache.catalina.startup.VersionLoggerListener.log OS Name:               Linux
org.apache.catalina.startup.VersionLoggerListener.log OS Version:            4.4.0-128-generic
org.apache.catalina.startup
 
.VersionLoggerListener.log Architecture:          amd64
org.apache.catalina.startup.VersionLoggerListener.log Java Home:             /usr/lib/jvm/java-7-oracle/jre
org.apache.catalina.startup.VersionLoggerListener.log JVM Version:           1.7.0_80-b15
org.apache.catalina.startup.VersionLoggerListener.log
 
 JVM Vendor:            Oracle Corporation
org.apache.catalina.startup.VersionLoggerListener.log CATALINA_BASE:         /var/lib/tomcat8
org.apache.catalina.startup.VersionLoggerListener.log CATALINA_HOME:         /usr/share/tomcat8
org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.util.logging.config.file=/var/lib/tomcat8/conf/logging.properties
org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager
org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.awt.headless=true
org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Xmx128m
org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -XX:+UseConcMarkSweepGC
org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.endorsed.dirs=/usr/share/tomcat8/endorsed
org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Dcatalina.base=/var/lib/tomcat8
org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Dcatalina.home=/usr/share/tomcat8
org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.io.tmpdir=/tmp/tomcat8-tomcat8-tmp
org.apache.coyote.AbstractProtocol.init Initializing ProtocolHandler ["http-nio-8080"]
org.apache.tomcat.util.net.NioSelectorPool.getSharedSelector Using a shared selector for servlet write/read
org.apache.catalina.startup.Catalina.load Initialization processed in 628 ms
org.apache.catalina.core.StandardService.startInternal Starting service Catalina
org.apache.catalina.core.StandardEngine.startInternal Starting Servlet Engine: Apache Tomcat/8.0.32 (Ubuntu)
[localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDescriptor Deploying configuration descriptor /etc/tomcat8/Catalina/localhost/examples.xml
[localhost-startStop-1] org.apache.catalina.core.ContainerBase.addChildInternal ContainerBase.addChild: start: 
 org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/examples]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:725)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:701)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717)
    at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:585)
    at org.apache.catalina.startup.HostConfig$DeployDescriptor.run(HostConfig.java:1794)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
    at java.util.concurrent.FutureTask.run(FutureTask.java:262)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NoSuchMethodError: java.util.concurrent.ConcurrentHashMap.keySet()Ljava/util/concurrent/ConcurrentHashMap$KeySetView;
    at org.apache.catalina.core.StandardContext.findParameters(StandardContext.java:3585)
    at org.apache.catalina.core.StandardContext.mergeParameters(StandardContext.java:5418)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5247)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)

從中可以看出Tomcat8使用的仍然是jdk1.7, 為何如此呢?
可能jdk1.7這個版本和Tomcat8版本不一致導致這個錯誤，需要更新到1.8試一下。
通過檢視/etc/init.d/tomcat8 檔案可以看到：

find_jdks()
{
    for java_version in 9 8 7
    do
        for jvmdir in /usr/lib/jvm/java-${java_version}-openjdk-* \
                      /usr/lib/jvm/jdk-${java_version}-oracle-* \
                      /usr/lib/jvm/jre-${java_version}-oracle-* \
                      /usr/lib/jvm/java-${java_version}-oracle
        do
            if [ -d "${jvmdir}" ]
            then
                JDK_DIRS="${JDK_DIRS} ${jvmdir}"
            fi
        done
    done

    # Add the paths for the JVMs packaged by the older versions of java-package (<< 0.52 as in Wheezy and Trusty)
    JDK_DIRS="${JDK_DIRS} /usr/lib/jvm/j2re1.7-oracle /usr/lib/jvm/j2sdk1.7-oracle"
}

預設按照這些路徑來查詢jdk，如果你安裝時不是按照這個路徑安裝的，那就找不到。

# tar xzvf jdk-8u171-linux-x64.tar.gz  -C /usr/lib/jvm/
# mv jdk1.8.0_171 java-8-oracle

然後修改環境變數，再次執行tomcat8： service tomcat8 restart
這次找到的是tomcat8，而且不再報錯。

jdk是下載包檔案安裝，
tomcat8是通過源安裝：
sudo apt-get install tomcat8 tomcat8-docs tomcat8-examples tomcat8-admin
沒有錯誤後，看通過 127.0.0.1:8080 檢視啟動是否正常。