3. Java Class Files#

Although, the previously introduced ABI implementations to Objective-C and Swift inspect executable files, this “ABI-like” module operates directly on Java class files. The general structure of the Java class file won’t be discussed here and is fairly well documented on Oracle’s documentation platform [1] .

Example usage of the provided API#

from umbrella.java import JavaClassFile

with open("/path/to/file.class", "rb") as fp:
    file = JavaClassFile(fp)

    # get the plain class name
    simple_name = file.get_simple_name()

    # iterator over all defined methods
    for method in file.jclass.methods:
        # retrieve the method's name
        name = file.get_constant_value(method.name_index)

    # iterate over all defined fields
    for field in file.jclass.fields:
        name = file.get_constant_value(field.name_index)
        access_flags: List[str] = field.access_flags.flags

    # list all class attributes
    for attribute in file.jclass.attributes:
        tag = attribute.name
        # based on the tag, each attribute should be handled differently
        ...

3.1. Structs#

Constant Pool: An overview of all used structs that occur in the constant pool.
Access Flags: A list of all defined access flags for different types of constants or attributes.
Attribute Structs: All defined attribute structs (except StackFrameMap).

class umbrella.java.ClassFile[source]#

Main structure to store all class-related data

magic: bytes = b'\xca\xfe\xba\xbe'#: The magic item supplies the magic number identifying the class file format; it has the value 0xCAFEBABE.

minor_version: uint16_t#: The values of the minor_version and major_version items represent the minor and major version numbers of this class file. These numbers together determine the class file format version. When a class file has a major version number of M and a minor version number of m, the format version of its class file is denoted as M.m. Consequently, class file format versions can be ordered lexicographically, for example, 1.5 < 2.0 < 2.1.

major_version: uint16_t#: The major version, as described above.

constant_pool: ConstantPool#: The constant pool for this class file.

access_flags: AccessFlags#: The value of the access_flags item is a mask of flags used to denote access permissions to and properties of this class or interface

this_class: uint16_t#: The value of the this_class item must be a valid index into the constant_pool table. The constant_pool entry at that index must be a CONSTANT_Class_info structure representing the class or interface defined by this class file.

super_class: uint16_t#: For a class, the value of the super_class item either must be zero or must be a valid index into the constant_pool table. If the value of the super_class item is nonzero, the constant_pool entry at that index must be a CONSTANT_Class_info structure representing the direct superclass of the class defined by this class file.

num_interfaces: uint16_t#: The value of the interfaces_count item gives the number of direct superinterfaces of this class or interface type.

interfaces: t.List[uint16_t]#: Each value in the interfaces array must be a valid index into the constant_pool table.

num_fields: uint16_t#: The value of the fields_count item gives the number of field_info structures in the fields table. The field_info structures represent all fields, both class variables and instance variables, declared by this class or interface type.

fields: t.List[attribute.FieldInfo]#: Each value in the fields table must be a field_info structure giving a complete description of a field in this class or interface

num_methods: uint16_t#: The value of the methods_count item gives the number of method_info structures in the methods table.

methods: t.List[attribute.MethodInfo]#: Each value in the methods table must be a method_info structure giving a complete description of a method in this class or interface.

num_attributes: uint16_t#: The value of the attributes_count item gives the number of attributes in the attributes table of this class.

attributes: t.List[attribute.AttributeInfo]#: Each value of the attributes table must be an AttributeInfo structure.

get_name() → str[source]#

get_super_class_name() → str | None[source]#

get_constant(index: int)[source]#

get_interface_names() → List[str][source]#

class umbrella.java.JavaClassFile(_JavaClassFile__stream: str)[source]#

property jclass: ClassFile#: The underlying java class file

get_simple_name() → str[source]#

Returns only the class name.

Returns:: the simple name of the underlying class
Return type:: str

get_package_name() → str[source]#

Generates the package name for the underlying class.

Returns:: the package name (e.g. "com.example.foo")
Return type:: str

get_source_name() → str | None[source]#

Returns the source code file name (if present)

Returns:: the source code file name
Return type:: t.Optional[str]

get_attribute(kind: str) → AttributeInfo | None[source]#

Tries to retrieve the first attribute with the given kind.

Parameters:: kind (str) – the attribute info tag (string)
Returns:: the first occurrence of the given attribute kind
Return type:: t.Optional[AttributeInfo]

get_constant_value(index: int) → str | int | float | Any[source]#

Returns the value associated to a constant entry.

Parameters:: index (int) – the constant pool relative index (starts with 1)
Returns:: the value or info object of no “value” field is defined
Return type:: t.Union[str, int, float, t.Any]

Footnotes