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java.lang.NoSuchMethodError:com.lfsenior.cn.TestDemo.getParam(Ljava/lang/String;)Ljava/util/Map; com.lfsenior.TestWeb.doGet(TestWeb.java:19)javax.servlet.http.HttpServlet.service(HttpServlet.java:622) javax.servlet.http.HttpServlet.service(HttpServlet.java:729) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
在通过javap -c -verbose TestWeb.class >> demo3.java 命令反编译的时候我们可以看到如下结果
当采用增量更新的方式的时候，如果我们更改了某个类的参数类型，即使更改的时候采用了多态，即使用父类替换子类的方式，依旧会出现问题，因为当这个方法被在其他地方使用并编译的时候，使用的参数类型依旧是子类，所有就会报NoSuchMethodError的错误。解决办法，将所有应该改方法的类重新编译后更新即可
测试代码地址：
https://gitee.com/lfsenior/STU/tree/master/testdemo
https://gitee.com/lfsenior/STU/tree/master/testdemoweb
反编译源码：
Classfile /Users/lisongli/Desktop/dlpan/stuproject/stu/testdemoweb/target/classes/com/lfsenior/TestWeb.class
Last modified Oct 8, 2018; size 1034 bytes
MD5 checksum f5f61c26872770e358bbdd5ffdbe59e5
Compiled from "TestWeb.java"
public class com.lfsenior.TestWeb extends javax.servlet.http.HttpServlet
minor version: 0
major version: 51
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #8.#29 // javax/servlet/http/HttpServlet."<init>":()V
#2 = InterfaceMethodref #30.#31 // javax/servlet/http/HttpServletResponse.getWriter:()Ljava/io/PrintWriter;
#3 = String #32 // test
#4 = Methodref #33.#34 // com/lfsenior/cn/TestDemo.getParam:(Ljava/lang/Object;)Ljava/util/Map;
#5 = Methodref #35.#36 // java/lang/Object.toString:()Ljava/lang/String;
#6 = Methodref #37.#38 // java/io/PrintWriter.write:(Ljava/lang/String;)V
#7 = Class #39 // com/lfsenior/TestWeb
#8 = Class #40 // javax/servlet/http/HttpServlet
#9 = Utf8 <init>
#10 = Utf8 ()V
#11 = Utf8 Code
#12 = Utf8 LineNumberTable
#13 = Utf8 LocalVariableTable
#14 = Utf8 this
#15 = Utf8 Lcom/lfsenior/TestWeb;
#16 = Utf8 doGet
#17 = Utf8 (Ljavax/servlet/http/HttpServletRequest;Ljavax/servlet/http/HttpServletResponse;)V
#18 = Utf8 req
#19 = Utf8 Ljavax/servlet/http/HttpServletRequest;
#20 = Utf8 resp
#21 = Utf8 Ljavax/servlet/http/HttpServletResponse;
#22 = Utf8 writer
#23 = Utf8 Ljava/io/PrintWriter;
#24 = Utf8 Exceptions
#25 = Class #41 // javax/servlet/ServletException
#26 = Class #42 // java/io/IOException
#27 = Utf8 SourceFile
#28 = Utf8 TestWeb.java
#29 = NameAndType #9:#10 // "<init>":()V
#30 = Class #43 // javax/servlet/http/HttpServletResponse
#31 = NameAndType #44:#45 // getWriter:()Ljava/io/PrintWriter;
#32 = Utf8 test
#33 = Class #46 // com/lfsenior/cn/TestDemo
#34 = NameAndType #47:#48 // getParam:(Ljava/lang/Object;)Ljava/util/Map;
#35 = Class #49 // java/lang/Object
#36 = NameAndType #50:#51 // toString:()Ljava/lang/String;
#37 = Class #52 // java/io/PrintWriter
#38 = NameAndType #53:#54 // write:(Ljava/lang/String;)V
#39 = Utf8 com/lfsenior/TestWeb
#40 = Utf8 javax/servlet/http/HttpServlet
#41 = Utf8 javax/servlet/ServletException
#42 = Utf8 java/io/IOException
#43 = Utf8 javax/servlet/http/HttpServletResponse
#44 = Utf8 getWriter
#45 = Utf8 ()Ljava/io/PrintWriter;
#46 = Utf8 com/lfsenior/cn/TestDemo
#47 = Utf8 getParam
#48 = Utf8 (Ljava/lang/Object;)Ljava/util/Map;
#49 = Utf8 java/lang/Object
#50 = Utf8 toString
#51 = Utf8 ()Ljava/lang/String;
#52 = Utf8 java/io/PrintWriter
#53 = Utf8 write
#54 = Utf8 (Ljava/lang/String;)V
{
public com.lfsenior.TestWeb();
descriptor: ()V
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #1 // Method javax/servlet/http/HttpServlet."<init>":()V
4: return
LineNumberTable:
line 15: 0
LocalVariableTable:
Start Length Slot Name Signature
0 5 0 this Lcom/lfsenior/TestWeb;
protected void doGet(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse) throws javax.servlet.ServletException, java.io.IOException;
descriptor: (Ljavax/servlet/http/HttpServletRequest;Ljavax/servlet/http/HttpServletResponse;)V
flags: ACC_PROTECTED
Code:
stack=2, locals=4, args_size=3
0: aload_2
1: invokeinterface #2, 1 // InterfaceMethod javax/servlet/http/HttpServletResponse.getWriter:()Ljava/io/PrintWriter;
6: astore_3
7: aload_3
8: ldc #3 // String test
10: invokestatic #4 // Method com/lfsenior/cn/TestDemo.getParam:(Ljava/lang/Object;)Ljava/util/Map;
13: invokevirtual #5 // Method java/lang/Object.toString:()Ljava/lang/String;
16: invokevirtual #6 // Method java/io/PrintWriter.write:(Ljava/lang/String;)V
19: return
LineNumberTable:
line 18: 0
line 19: 7
line 20: 19
LocalVariableTable:
Start Length Slot Name Signature
0 20 0 this Lcom/lfsenior/TestWeb;
0 20 1 req Ljavax/servlet/http/HttpServletRequest;
0 20 2 resp Ljavax/servlet/http/HttpServletResponse;
7 13 3 writer Ljava/io/PrintWriter;
Exceptions:
throws javax.servlet.ServletException, java.io.IOException
}
SourceFile: "TestWeb.java"