1、 错误内容：java.lang.NoSuchMethodError: com.Boot: method <init>()V not found
此提示内容指，com.Boot没有参数为空的构造函数。提示中指明了异常所在的类和对应的函数。
2、 java文档： 说的很清楚了，是类的变化不兼容导致的异常。通俗的说法是，调用方使用的类定义和加载的类定义不一样，加载的类实际上没有将要调用的方法。
/*** Thrown if an application tries to call a specified method of a* class (either static or instance), and that class no longer has a* definition of that method.* <p>* Normally, this error is caught by the compiler; this error can* only occur at run time if the definition of a class has* incompatibly changed.** @author unascribed* @since JDK1.0*/
public
class NoSuchMethodError extends IncompatibleClassChangeError {
3、 如何制造一个NoSuchMethodError：
这里提供两个java代码。放在com目录下。依次执行以下命令：
javac com/Boot.javajavac com/Cloud.javavim com/Boot.java 把Boot的无参构造函数注释掉，把有参构造函数的注释打开javac com/Boot.java 重新编译Boot的类文件，最终结果没有无参构造函数java com/Cloud 此处会出现NoSuchMethodError异常
方法提供方
package com;public class Boot{private String name;// public Boot (String name){// this.name = name;// } 注意这里的两个构造函数。public Boot (){}public void run(){System.out.println(name);}
}======================
调用方
package com;
import com.Boot;
public class Cloud{public Cloud (){}public static void main(String[] args){new Boot().run();}
}
4、原因说明
实际使用的类文件不配套导致的异常。即通常所说的jar包版本不一致导致此问题。
5、实际举例
Spring Boot 2.x 使用 feign 出现此错误。Spring Cloud 1.1调用的构造函数是 new SpringApplicationBuilder(new Object[0]) ，但Spring Boot 2.1 提供的构造函数只有一个
public SpringApplicationBuilder(Class... sources) {
this.application = this.createSpringApplication(sources);
}
java.lang.NoSuchMethodError: org.springframework.boot.builder.SpringApplicationBuilder.<init>([Ljava/lang/Object;)Vat org.springframework.cloud.bootstrap.BootstrapApplicationListener.bootstrapServiceContext(BootstrapApplicationListener.java:120)at org.springframework.cloud.bootstrap.BootstrapApplicationListener.onApplicationEvent(BootstrapApplicationListener.java:84)at org.springframework.cloud.bootstrap.BootstrapApplicationListener.onApplicationEvent(BootstrapApplicationListener.java:62)at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:127)at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:76)at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:53)at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:342)at org.springframework.boot.SpringApplication.run(SpringApplication.java:305)at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215)at org.springframework.boot.SpringApplication.run(SpringApplication.java:1204)at com.Application.main(Application.java:22)
`
6、解决方式：换依赖jar的版本
