java Class文件结构解析常量池字节码

ClassFile {
    u4             magic;
    u2             minor_version;
    u2             major_version;
    u2             constant_pool_count;
    cp_info        constant_pool[constant_pool_count-1];
    u2             access_flags;
    u2             this_class;
    u2             super_class;
    u2             interfaces_count;
    u2             interfaces[interfaces_count];
    u2             fields_count;
    field_info     fields[fields_count];
    u2             methods_count;
    method_info    methods[methods_count];
    u2             attributes_count;
    attribute_info attributes[attributes_count];
}

// Check version numbers - we check this even with verifier off
  if (!is_supported_version(major_version, minor_version)) {
    if (name == NULL) {
      Exceptions::fthrow(
        THREAD_AND_LOCATION,
        vmSymbols::java_lang_UnsupportedClassVersionError(),
        "Unsupported major.minor version %u.%u",
        major_version,
        minor_version);
    } 

cp_info {
    u1 tag;  //表示常量的类型
    u1 info[];  //具体常量的内容结构 不同类型常量有不同的结构
}

/*常量类型*/
Constant Type    Value
CONSTANT_Class    7
CONSTANT_Fieldref    9
CONSTANT_Methodref    10
CONSTANT_InterfaceMethodref    11
CONSTANT_String    8
CONSTANT_Integer    3
CONSTANT_Float    4
CONSTANT_Long    5
CONSTANT_Double    6
CONSTANT_NameAndType    12
CONSTANT_Utf8    1
CONSTANT_MethodHandle    15
CONSTANT_MethodType    16
CONSTANT_InvokeDynamic    18

CONSTANT_Utf8_info {
    u1 tag;
    u2 length;  //字符串长度
    u1 bytes[length]; //字符串数据（utf-8编码）
}

attribute_info {
    u2 attribute_name_index;
    u4 attribute_length;
    u1 info[attribute_length];
}

//一部分Attribute Name
Attribute    Section    class file    Java SE
ConstantValue    §4.7.2    45.3    1.0.2
Code    §4.7.3    45.3    1.0.2
StackMapTable    §4.7.4    50.0    6
Exceptions    §4.7.5    45.3    1.0.2
InnerClasses    §4.7.6    45.3    1.1
//.......

Code_attribute {
    u2 attribute_name_index;
    u4 attribute_length;
    u2 max_stack;  //最大栈深度
    u2 max_locals;  //局部变量数量
    u4 code_length; //字节码内容长度
    u1 code[code_length];  //字节码内容
    u2 exception_table_length;  //异常处理表 由try,catch/finaly 产生
    {   u2 start_pc;
        u2 end_pc;
        u2 handler_pc;
        u2 catch_type;
    } exception_table[exception_table_length];
    u2 attributes_count;
    attribute_info attributes[attributes_count];
}

method_info {
    u2             access_flags;
    u2             name_index;
    u2             descriptor_index;
    u2             attributes_count;
//一定会包含一个code属性项
    attribute_info attributes[attributes_count];
}

field_info {
    u2             access_flags;
    u2             name_index;
    u2             descriptor_index;
    u2             attributes_count;
    attribute_info attributes[attributes_count];
}