J'ai récemment commencé à créer une JVM, et maintenant j'ai beaucoup d'opportunités de voir à quoi ressemblent les fichiers de classe réels.
Je pourrais utiliser javap, mais je voulais un outil qui rendrait le fichier de classe entier hiérarchique et le sortirait, donc pour la pratique, j'ai créé un outil qui génère la structure du fichier de classe au format JSON.
https://github.com/chgzm/cls2json Basé sur la spécification Java SE 11 Edition.
Si vous générez un fichier de classe à partir de Hello.java comme indiqué ci-dessous et que vous le transmettez à l'outil, JSON sera généré.
Hello.java
public class Hello {
public static void main(String[] args) {
System.out.println("Hello, World.");
}
}
$ javac Hello.java
$ ./cls2json Hello.class
{"magic":"0xcafebabe","minor_version":0,"major_version":55,"constant_pool_count":29,"constant_pool":["null",{"tag":10,"class_index":6,"name_and_type_index":15},{"tag":9,"class_index":16,"name_and_type_index":17},{"tag":8,"string_index":18},{"tag":10,"class_index":19,"name_and_type_index":20},{"tag":7,"name_index":21},{"tag":7,"name_index":22},{"tag":1,"length":6,"bytes":"<init>"},{"tag":1,"length":3,"bytes":"()V"},{"tag":1,"length":4,"bytes":"Code"},{"tag":1,"length":15,"bytes":"LineNumberTable"},{"tag":1,"length":4,"bytes":"main"},{"tag":1,"length":22,"bytes":"([Ljava/lang/String;)V"},{"tag":1,"length":10,"bytes":"SourceFile"},{"tag":1,"length":10,"bytes":"Hello.java"},{"tag":12,"name_index":7,"descriptor_index":8},{"tag":7,"name_index":23},{"tag":12,"name_index":24,"descriptor_index":25},{"tag":1,"length":13,"bytes":"Hello, World."},{"tag":7,"name_index":26},{"tag":12,"name_index":27,"descriptor_index":28},{"tag":1,"length":5,"bytes":"Hello"},{"tag":1,"length":16,"bytes":"java/lang/Object"},{"tag":1,"length":16,"bytes":"java/lang/System"},{"tag":1,"length":3,"bytes":"out"},{"tag":1,"length":21,"bytes":"Ljava/io/PrintStream;"},{"tag":1,"length":19,"bytes":"java/io/PrintStream"},{"tag":1,"length":7,"bytes":"println"},{"tag":1,"length":21,"bytes":"(Ljava/lang/String;)V"}],"access_Flags":"0x33","this_class":5,"super_class":6,"interfaces_count":0,"interfaces":[],"fields_count":0,"fields":[],"methods_count":2,"methods":[{"access_flags":1,"name_index":7,"descriptor_index":8,"attributes_count":1,"attributes":[{"attribute_name_index":9,"attribute_length":29,"max_stack":1,"max_locals":1,"code_length":5,"code":[42,183,0,1,177],"exception_table_length":0,"exception_table":[],"attributes_count":1,"attributes":[{"attribute_name_index":10,"attribute_length":6,"line_number_table_length":1,"line_number_table":[{"start_pc":0,"line_number":1}]}]}]}, {"access_flags":9,"name_index":11,"descriptor_index":12,"attributes_count":1,"attributes":[{"attribute_name_index":9,"attribute_length":37,"max_stack":2,"max_locals":1,"code_length":9,"code":[178,0,2,18,3,182,0,4,177],"exception_table_length":0,"exception_table":[],"attributes_count":1,"attributes":[{"attribute_name_index":10,"attribute_length":10,"line_number_table_length":2,"line_number_table":[{"start_pc":0,"line_number":3},{"start_pc":8,"line_number":4}]}]}]}],"attributes_count":1,"attributes":[{"attribute_name_index":13,"attribute_length":2,"source_file_index":14}]}
Vous pouvez voir la structure hiérarchique en la formatant avec jq.
$ ./cls2json Hello.class | jq
{
"magic": "0xcafebabe",
"minor_version": 0,
"major_version": 55,
"constant_pool_count": 29,
"constant_pool": [
"null",
{
"tag": 10,
"class_index": 6,
"name_and_type_index": 15
},
{
"tag": 9,
"class_index": 16,
"name_and_type_index": 17
},
{
"tag": 8,
"string_index": 18
},
{
"tag": 10,
"class_index": 19,
"name_and_type_index": 20
},
{
"tag": 7,
"name_index": 21
},
{
"tag": 7,
"name_index": 22
},
{
"tag": 1,
"length": 6,
"bytes": "<init>"
},
{
"tag": 1,
"length": 3,
"bytes": "()V"
},
{
"tag": 1,
"length": 4,
"bytes": "Code"
},
{
"tag": 1,
"length": 15,
"bytes": "LineNumberTable"
},
{
"tag": 1,
"length": 4,
"bytes": "main"
},
{
"tag": 1,
"length": 22,
"bytes": "([Ljava/lang/String;)V"
},
{
"tag": 1,
"length": 10,
"bytes": "SourceFile"
},
{
"tag": 1,
"length": 10,
"bytes": "Hello.java"
},
{
"tag": 12,
"name_index": 7,
"descriptor_index": 8
},
{
"tag": 7,
"name_index": 23
},
{
"tag": 12,
"name_index": 24,
"descriptor_index": 25
},
{
"tag": 1,
"length": 13,
"bytes": "Hello, World."
},
{
"tag": 7,
"name_index": 26
},
{
"tag": 12,
"name_index": 27,
"descriptor_index": 28
},
{
"tag": 1,
"length": 5,
"bytes": "Hello"
},
{
"tag": 1,
"length": 16,
"bytes": "java/lang/Object"
},
{
"tag": 1,
"length": 16,
"bytes": "java/lang/System"
},
{
"tag": 1,
"length": 3,
"bytes": "out"
},
{
"tag": 1,
"length": 21,
"bytes": "Ljava/io/PrintStream;"
},
{
"tag": 1,
"length": 19,
"bytes": "java/io/PrintStream"
},
{
"tag": 1,
"length": 7,
"bytes": "println"
},
{
"tag": 1,
"length": 21,
"bytes": "(Ljava/lang/String;)V"
}
],
"access_Flags": "0x33",
"this_class": 5,
"super_class": 6,
"interfaces_count": 0,
"interfaces": [],
"fields_count": 0,
"fields": [],
"methods_count": 2,
"methods": [
{
"access_flags": 1,
"name_index": 7,
"descriptor_index": 8,
"attributes_count": 1,
"attributes": [
{
"attribute_name_index": 9,
"attribute_length": 29,
"max_stack": 1,
"max_locals": 1,
"code_length": 5,
"code": [
42,
183,
0,
1,
177
],
"exception_table_length": 0,
"exception_table": [],
"attributes_count": 1,
"attributes": [
{
"attribute_name_index": 10,
"attribute_length": 6,
"line_number_table_length": 1,
"line_number_table": [
{
"start_pc": 0,
"line_number": 1
}
]
}
]
}
]
},
{
"access_flags": 9,
"name_index": 11,
"descriptor_index": 12,
"attributes_count": 1,
"attributes": [
{
"attribute_name_index": 9,
"attribute_length": 37,
"max_stack": 2,
"max_locals": 1,
"code_length": 9,
"code": [
178,
0,
2,
18,
3,
182,
0,
4,
177
],
"exception_table_length": 0,
"exception_table": [],
"attributes_count": 1,
"attributes": [
{
"attribute_name_index": 10,
"attribute_length": 10,
"line_number_table_length": 2,
"line_number_table": [
{
"start_pc": 0,
"line_number": 3
},
{
"start_pc": 8,
"line_number": 4
}
]
}
]
}
]
}
],
"attributes_count": 1,
"attributes": [
{
"attribute_name_index": 13,
"attribute_length": 2,
"source_file_index": 14
}
]
}
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