1 简介
Class文件是一组以字节为基础单位的二进制流。
JVM的数据入口就是我们平时代码编译后的Class文件，那么要搞懂JVM的原理之前，就要了解Class文件里边都是什么，才能更好的理解JVM原理。
内容比较多，希望看到的小伙伴也能自己动手，边看边解析一个自己的Class文件，光看不操作其实等于白看，因为过两天你就忘了。
2 准备工作
一个Class文件 、NotePad++文本文件查看
Class文件，用文本工具打开，是一堆乱码，因为它本身是二进制流的。
用NotePad++的插件有个HEX插件，就是以16进制的方式显示。
javap -verbose .class 反编译看看Class文件信息
1 kuku@DESKTOP-KQS9B3J MINGW64 ~/Desktop
2 $ javap -verbose BscDictService.class
3 Classfile /C:/Users/kuku/Desktop/BscDictService.class
4 Last modified 2022-6-9; size 1727 bytes
5 MD5 checksum 87ad0a7a75e3755bdbb266ee5e77a998
6 Compiled from "BscDictService.java"
7 public interface com.goldjet.appservice.customs.application.bsc.BscDictService extends com.bitsun.core.framwork.application.IApplicationService
8 minor version: 0
9 major version: 52
10 flags: ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
11 Constant pool:
12 #1 = Class #31 // com/goldjet/appservice/customs/application/bsc/BscDictService
13 #2 = Class #32 // java/lang/Object
14 #3 = Class #33 // com/bitsun/core/framwork/application/IApplicationService
15 #4 = Utf8 save
16 #5 = Utf8 (Lcom/goldjet/appservice/customs/dto/req/bcs/BscDictReqDto;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
17 #6 = Utf8 MethodParameters
18 #7 = Utf8 reqDto
19 #8 = Utf8 deleteByIds
20 #9 = Utf8 (Ljava/lang/String;)Ljava/lang/Void;
21 #10 = Utf8 ids
22 #11 = Utf8 doPager
23 #12 = Utf8 (Ljava/util/Map;)Lcom/bitsun/core/common/persistence/Pager;
24 #13 = Utf8 params
25 #14 = Utf8 Signature
26 #15 = Utf8 (Ljava/util/Map<Ljava/lang/String;Ljava/lang/Object;>;)Lcom/bitsun/core/common/persistence/Pager<Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;>;
27 #16 = Utf8 selectOne
28 #17 = Utf8 (Ljava/lang/Long;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
29 #18 = Utf8 id
30 #19 = Utf8 (Ljava/util/Map;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
31 #20 = Utf8 (Ljava/util/Map<Ljava/lang/String;Ljava/lang/Object;>;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
32 #21 = Utf8 updateProps
33 #22 = Utf8 (Ljava/lang/Long;Ljava/util/Map;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
34 #23 = Utf8 (Ljava/lang/Long;Ljava/util/Map<Ljava/lang/String;Ljava/lang/Object;>;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
35 #24 = Utf8 (Ljava/lang/Long;Lcom/goldjet/appservice/customs/dto/req/bcs/BscDictReqDto;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
36 #25 = Utf8 selectDictItemByDictCode
37 #26 = Utf8 (Ljava/lang/String;)Ljava/util/List;
38 #27 = Utf8 dictCode
39 #28 = Utf8 (Ljava/lang/String;)Ljava/util/List<Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictItemResDto;>;
40 #29 = Utf8 SourceFile
41 #30 = Utf8 BscDictService.java
42 #31 = Utf8 com/goldjet/appservice/customs/application/bsc/BscDictService
43 #32 = Utf8 java/lang/Object
44 #33 = Utf8 com/bitsun/core/framwork/application/IApplicationService
45 {
46 public abstract com.goldjet.appservice.customs.dto.res.bcs.BscDictResDto save(com.goldjet.appservice.customs.dto.req.bcs.BscDictReqDto);
47 descriptor: (Lcom/goldjet/appservice/customs/dto/req/bcs/BscDictReqDto;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
48 flags: ACC_PUBLIC, ACC_ABSTRACT
49 MethodParameters:
50 Name Flags
51 reqDto
52
53 public abstract java.lang.Void deleteByIds(java.lang.String);
54 descriptor: (Ljava/lang/String;)Ljava/lang/Void;
55 flags: ACC_PUBLIC, ACC_ABSTRACT
56 MethodParameters:
57 Name Flags
58 ids
59
60 public abstract com.bitsun.core.common.persistence.Pager<com.goldjet.appservice.customs.dto.res.bcs.BscDictResDto> doPager(java.util.Map<java.lang.String, java.lang.Object>);
61 descriptor: (Ljava/util/Map;)Lcom/bitsun/core/common/persistence/Pager;
62 flags: ACC_PUBLIC, ACC_ABSTRACT
63 MethodParameters:
64 Name Flags
65 params
66 Signature: #15 // (Ljava/util/Map<Ljava/lang/String;Ljava/lang/Object;>;)Lcom/bitsun/core/common/persistence/Pager<Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;>;
67
68 public abstract com.goldjet.appservice.customs.dto.res.bcs.BscDictResDto selectOne(java.lang.Long);
69 descriptor: (Ljava/lang/Long;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
70 flags: ACC_PUBLIC, ACC_ABSTRACT
71 MethodParameters:
72 Name Flags
73 id
74
75 public abstract com.goldjet.appservice.customs.dto.res.bcs.BscDictResDto selectOne(java.util.Map<java.lang.String, java.lang.Object>);
76 descriptor: (Ljava/util/Map;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
77 flags: ACC_PUBLIC, ACC_ABSTRACT
78 MethodParameters:
79 Name Flags
80 params
81 Signature: #20 // (Ljava/util/Map<Ljava/lang/String;Ljava/lang/Object;>;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
82
83 public abstract com.goldjet.appservice.customs.dto.res.bcs.BscDictResDto updateProps(java.lang.Long, java.util.Map<java.lang.String, java.lang.Object>);
84 descriptor: (Ljava/lang/Long;Ljava/util/Map;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
85 flags: ACC_PUBLIC, ACC_ABSTRACT
86 MethodParameters:
87 Name Flags
88 id
89 params
90 Signature: #23 // (Ljava/lang/Long;Ljava/util/Map<Ljava/lang/String;Ljava/lang/Object;>;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
91
92 public abstract com.goldjet.appservice.customs.dto.res.bcs.BscDictResDto updateProps(java.lang.Long, com.goldjet.appservice.customs.dto.req.bcs.BscDictReqDto);
93 descriptor: (Ljava/lang/Long;Lcom/goldjet/appservice/customs/dto/req/bcs/BscDictReqDto;)Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictResDto;
94 flags: ACC_PUBLIC, ACC_ABSTRACT
95 MethodParameters:
96 Name Flags
97 id
98 reqDto
99
100 public abstract java.util.List<com.goldjet.appservice.customs.dto.res.bcs.BscDictItemResDto> selectDictItemByDictCode(java.lang.String);
101 descriptor: (Ljava/lang/String;)Ljava/util/List;
102 flags: ACC_PUBLIC, ACC_ABSTRACT
103 MethodParameters:
104 Name Flags
105 dictCode
106 Signature: #28 // (Ljava/lang/String;)Ljava/util/List<Lcom/goldjet/appservice/customs/dto/res/bcs/BscDictItemResDto;>;
107 }
108 SourceFile: "BscDictService.java"
View Code
3 文件结构
Class文件是一组以8位字节为基础单位的二进制流，内容是以《Java虚拟机规范》规定的一种固定的格式存储数据。存储数据用到了两个数据类型：“无符号数”和“表”。
无符号数：无符号数是基本数据类型，以u1、u2、u4、u8来分别代表1个字节、2个字节、4个字节和8个字节的无符号数，无符号数可以用来描述数字、索引引用、数量表或者按照UTF-8编码构成字符串值。
表：由多个无符号数或者其他表作为数据项构成的复合数据类型，以“_info”结尾，用户描述有层次关系的复合结构的数据。
下图是《Java虚拟机规范》规定的Class文件的固定格式，所有Class文件均按照一下格式存储内容。(注意：每个class文件内容都是按照以下列表按列表中从上到下顺序组成，如果某些类型不涉及可以为空)
4 文件结构分析
4.1 魔数
标签：appservice,Ljava,dto,Utf8,customs,goldjet,详解,JVM,Class From： https://www.cnblogs.com/kukuxjx/p/17107692.html