老系统使用的是Spring2.5.5，准备把老系统换到新的服务器上，安装好了新版的JDK11，却发现无法启动tomcat，查看tomcat/logs/catalina.out的日志：
Unexpected exception parsing XML document from class path resource [applicationContext-dao.xml]; nested exception is java.lang.IllegalStateException: Context namespace element 'annotation-config' and its parser class [org.springframework.context.annotation.AnnotationConfigBeanDefinitionParser] are only available on JDK 1.5 and higher Caused by: java.lang.IllegalStateException: Context namespace element 'annotation-config' and its parser class [org.springframework.context.annotation.AnnotationConfigBeanDefinitionParser] are only available on JDK 1.5 and higher
发现Spring居然监测到的JDK版本是1.5以下。
如果要换Spring的话，老系统不知道要改写什么东西，工程量比较大，找到网上一个解决方案（是解决1.8的JDK的，我稍加修改了下，解决1.8以上全部的JDK），总体思路是修改Spring判断JDK版本的类，重新编译并覆盖掉原来的。
在项目中，创建org.springframework.core这个package，然后新建一个类：JdkVersion.java，内容如下：
/*
* Copyright (c) 2021.
*
* 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.
*
*/
package org.springframework.core;
/**
* @author Terry E-mail: yaoxinghuo at 126 dot com
* @date 2021-6-25 14:19
* @description
*/
public class JdkVersion {
public static final int JAVA_13 = 0;
public static final int JAVA_14 = 1;
public static final int JAVA_15 = 2;
public static final int JAVA_16 = 3;
public static final int JAVA_17 = 4;
private static final String javaVersion = System.getProperty("java.version");
private static final int majorJavaVersion;
public static String getJavaVersion() {
return javaVersion;
}
public static int getMajorJavaVersion() {
return majorJavaVersion;
}
public static boolean isAtLeastJava14() {
return true;
}
public static boolean isAtLeastJava15() {
return getMajorJavaVersion() >= 2;
}
public static boolean isAtLeastJava16() {
return getMajorJavaVersion() >= 3;
}
static {
if (javaVersion.indexOf("1.7.") != -1) {
majorJavaVersion = 4;
} else if (javaVersion.indexOf("1.6.") != -1) {
majorJavaVersion = 3;
} else if (javaVersion.indexOf("1.5.") != -1) {
majorJavaVersion = 2;
} else {
majorJavaVersion = 5; //修改这里，监测JDK，都当成高版本1.8以上，相信也不可能找到再旧版的JDK了！
}
}
}
重新编译了一下，在 build/classes/org/springframework/core/JdkVersion.class 这里找到JdkVersion.class，然后用解压缩软件打开项目的lib目录里的spring-2.5.5.jar，把里面的org/springframework/core里的JdkVersion.class替换成我们编译出来的，再放回原来的lib下，就可以顺利启动Tomcat啦！
如果你懒得编译，我已经把编译修改好的spring.2.5.5.jar传到github上了，供有需要的下载：
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