Ich habe vor kurzem angefangen, eine JVM zu erstellen, und jetzt habe ich viele Möglichkeiten zu sehen, wie die tatsächlichen Klassendateien aussehen.
Ich könnte javap verwenden, aber ich wollte ein Tool, das die gesamte Klassendatei hierarchisch macht und ausgibt. In der Praxis habe ich ein Tool erstellt, das die Struktur der Klassendatei als JSON ausgibt.
https://github.com/chgzm/cls2json Basierend auf der Java SE 11 Edition-Spezifikation.
Wenn Sie eine Klassendatei aus "Hello.java" wie unten gezeigt generieren und dem Tool zuführen, wird JSON ausgegeben.
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}]}
Sie können die hierarchische Struktur sehen, indem Sie sie mit jq formatieren.
$ ./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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