问题：启动tomcat报找不到JAVA_HOME或者JRE_HOME环境变量的问题

一、错误来源

在非linux系统上(即外部)启动tomcat时显示的错误

二、报错原文

Neither the JAVA_HOME nor the JRE_HOME environment variable is defined
At least one of these environment variable is needed to run this program

三、错误译文

JAVA_HOME和JRE_HOME环境变量都没有定义
运行这个程序至少需要这些环境变量中的一个

四、错误思索

我明明在/etc/profile这个文件里面添加了java和tomcat的环境变量啊，为什么还出错，而在服务器上启动tomcat就不报这个错误

五、粗略分析错误原因

在服务器上启动tomcat不报错是因为启动tomcat时区/etc/profile文件里面找到了java和tomcat的环境变量，所以顺利启动，而在外部启动tomcat时，tomcat程序首先调用startup.sh脚本文件，startup.sh又去调用catalina.sh这个脚本文件，而catalina.sh脚本文件又会去setclasspath.sh这个脚本文件里面寻找tomcat变量环境，这是因为setclasspath.sh文件就是tomcat变量环境脚本，这是因为这个脚本默认是没有在脚本开头申请java和jdk的变量环境刘静的，因此报错，setclasspath.sh的路径是：
/usr/local/tomcat/bin/setclasspath.sh
（因为我的tomcat是装在/usr/local路径下了，所以我的是这个，你们要按照你们的安装路径在查找）

六、查看setclasspath.sh脚本文件，精确分析原因

setclasspath.sh脚本原文以及中文解释如下:

#!/bin/sh
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# -----------------------------------------------------------------------------
#  Set CLASSPATH and Java options
#
#  $Id: setclasspath.sh 795037 2009-07-17 10:52:16Z markt $
# -----------------------------------------------------------------------------
# Make sure prerequisite environment variables are set
#因为setclasspath.sh脚本是被catalina.sh调用，所以可以继承catalina.sh中的变量申明
if [ -z "$JAVA_HOME" -a -z "$JRE_HOME" ]; then
#判断用户有没有提前做$JAVA_HOME和$JRE_HOME全局变量声明，如果都没进行申明
  # Bugzilla 37284 (reviewed).
  if $darwin; then
  #要理解这个判断，先看下startup.sh和shutdown.sh就会明白
  #这个是win仿真unix不用管下面两个语句
    if [ -d "/System/Library/Frameworks/JavaVM.framework/Versions/CurrentJDK/Home" ]; then
      export JAVA_HOME="/System/Library/Frameworks/JavaVM.framework/Versions/CurrentJDK/Home"
    fi
  else
  #其他环境没有申明，那么系统自己想办法找这两个变量的路径
    JAVA_PATH=`which java 2>/dev/null`
#此语句可以把java命令位置找出来
    if [ "x$JAVA_PATH" != "x" ]; then
#如果能找出java路径，则可以定位到java命令的路径，经过作者验证不是java的装路径
#所以通过此处就可以看出，老鸟们为什么都要自己指定这两个变量了
      JAVA_PATH=`dirname $JAVA_PATH 2>/dev/null`
      JRE_HOME=`dirname $JAVA_PATH 2>/dev/null`
    fi
    if [ "x$JRE_HOME" = "x" ]; then
#如果找不到java路径，那么就看有没有/usr/bin/java这个执行文件，有的话就它了，没有就算了
      # XXX: Should we try other locations?
      if [ -x /usr/bin/java ]; then
        JRE_HOME=/usr
      fi
    fi
  fi

  if [ -z "$JAVA_HOME" -a -z "$JRE_HOME" ]; then
  #再验证一边，有没有这两个变量，没有不好意思，我不执行了，退出
  #这个exit 1 不但是结束setclasspath.sh，会彻底退出catalina.sh脚本的
  #对于在脚本中引用脚本的童鞋们，就需要注意了，小心使用exit。 
    echo "Neither the JAVA_HOME nor the JRE_HOME environment variable is defined"
    echo "At least one of these environment variable is needed to run this program"
    exit 1
  fi
fi
if [ -z "$JAVA_HOME" -a "$1" = "debug" ]; then
  echo "JAVA_HOME should point to a JDK in order to run in debug mode."
  exit 1
fi
if [ -z "$JRE_HOME" ]; then
  JRE_HOME="$JAVA_HOME"
fi
# If we're running under jdb, we need a full jdk.
if [ "$1" = "debug" ] ; then
  if [ "$os400" = "true" ]; then
    if [ ! -x "$JAVA_HOME"/bin/java -o ! -x "$JAVA_HOME"/bin/javac ]; then
      echo "The JAVA_HOME environment variable is not defined correctly"
      echo "This environment variable is needed to run this program"
      echo "NB: JAVA_HOME should point to a JDK not a JRE"
      exit 1
    fi
  else
    if [ ! -x "$JAVA_HOME"/bin/java -o ! -x "$JAVA_HOME"/bin/jdb -o ! -x "$JAVA_HOME"/bin/javac ]; then
      echo "The JAVA_HOME environment variable is not defined correctly"
      echo "This environment variable is needed to run this program"
      echo "NB: JAVA_HOME should point to a JDK not a JRE"
      exit 1
    fi
  fi
fi
#上段的代码都是在确认$JAVA_HOME和$JRE_HOME变量的申明情况及后续的解决过程
if [ -z "$BASEDIR" ]; then
#对"$BASEDIR变量的检查，木有的话就退出
  echo "The BASEDIR environment variable is not defined"
  echo "This environment variable is needed to run this program"
  exit 1
fi
if [ ! -x "$BASEDIR"/bin/setclasspath.sh ]; then
#确认"$BASEDIR"/bin/setclasspath.sh有木有，木有还是退出
  if $os400; then
    # -x will Only work on the os400 if the files are:
    # 1. owned by the user
    # 2. owned by the PRIMARY group of the user
    # this will not work if the user belongs in secondary groups
    eval
#eval不清楚嘛意思
  else 
    echo "The BASEDIR environment variable is not defined correctly"
    echo "This environment variable is needed to run this program"
    exit 1
  fi
fi
# Don't override the endorsed dir if the user has set it previously
#这个是确认JAVA_ENDORSED_DIRS的位置
if [ -z "$JAVA_ENDORSED_DIRS" ]; then
  # Set the default -Djava.endorsed.dirs argument
  JAVA_ENDORSED_DIRS="$BASEDIR"/endorsed
fi
# OSX hack to CLASSPATH
JIKESPATH=
if [ `uname -s` = "Darwin" ]; then
  OSXHACK="/System/Library/Frameworks/JavaVM.framework/Versions/CurrentJDK/Classes"
  if [ -d "$OSXHACK" ]; then
    for i in "$OSXHACK"/*.jar; do
      JIKESPATH="$JIKESPATH":"$i"
    done
  fi
fi
# Set standard commands for invoking Java.
#这句是响当当的重要，确定了$_RUNJAVA的值
_RUNJAVA="$JRE_HOME"/bin/java
if [ "$os400" != "true" ]; then
  _RUNJDB="$JAVA_HOME"/bin/jdb
fi

说明：通过对这个脚本的分析，我们可以看到，这个脚本就做了一件事情，检查各种变量是否赋值，验证tomcat启动停止需要涉及到的文件，保障tomcat顺利启动停止。而我们报错就是因为它在全文搜索了半天结果一直找不到JRE_HOME和JAVA_HOME这两个变量到底在哪。

七、解决方案
在setclasspath.sh脚本文件的所有没有注释的行的开头加入截图中的两行即可：

最后重启tomcat就解决了问题。

转载于:https://blog.51cto.com/zpf666/2336199