Provides the implementation of the Zip file system provider. The Zip file system provider treats the contents of a Zip or JAR file as a file system.

Accessing a Zip File System

The FileSystems newFileSystem static factory methods can be used to:

• Create a Zip file system
• Open an existing file as a Zip file system

The Zip file system provider does not support opening an existing Zip file that contains entries with "." or ".." in its name elements.

URI Scheme Used to Identify the Zip File System

The URI scheme that identifies the ZIP file system is jar.

POSIX file attributes

A Zip file system supports a file attribute view named "zip" that defines the following file attribute:

Supported attributes

Name	Type
permissions	Set<PosixFilePermission>

The "permissions" attribute is the set of access permissions that are optionally stored for entries in a Zip file. The value of the attribute is null for entries that do not have access permissions. Zip file systems do not enforce access permissions.

The "permissions" attribute may be read and set using the Files.getAttribute and Files.setAttribute methods. The following example uses these methods to read and set the attribute:

 
     Set<PosixFilePermission> perms = Files.getAttribute(entry, "zip:permissions");
     if (perms == null) {
         perms = PosixFilePermissions.fromString("rw-rw-rw-");
         Files.setAttribute(entry, "zip:permissions", perms);
     }
  

In addition to the "zip" view, a Zip file system optionally supports the PosixFileAttributeView ("posix"). This view extends the "basic" view with type safe access to the owner, group-owner, and permissions attributes. The "posix" view is only supported when the Zip file system is created with the provider property "enablePosixFileAttributes" set to "true". The following creates a file system with this property and reads the access permissions of a file:

 
     var env = Map.of("enablePosixFileAttributes", "true");
     try (FileSystem fs = FileSystems.newFileSystem(file, env) {
         Path entry = fs.getPath("entry");
         Set<PosixFilePermission> perms = Files.getPosixFilePermissions(entry);
     }
  

The file owner and group owner attributes are not persisted, meaning they are not stored in the zip file. The "defaultOwner" and "defaultGroup" provider properties (listed below) can be used to configure the default values for these attributes. If these properties are not set then the file owner defaults to the owner of the zip file, and the group owner defaults to the zip file's group owner (or the file owner on platforms that don't support a group owner).

The "permissions" attribute is not optional in the "posix" view so a default set of permissions are used for entries that do not have access permissions stored in the Zip file. The default set of permissions are

• OWNER_READ
• OWNER_WRITE
• GROUP_READ

The default permissions can be configured with the "defaultPermissions" property described below.

Zip File System Properties

The following properties may be specified when creating a Zip file system:

Configurable properties that may be specified when creating a new Zip file system

Property Name	Data Type	Default Value	Description
create	String or Boolean	false	If the value is true, the Zip file system provider creates a new Zip or JAR file if it does not exist.
encoding	String	UTF-8	The value indicates the encoding scheme for the names of the entries in the Zip or JAR file.
enablePosixFileAttributes	String or Boolean	false	If the value is true, the Zip file system will support the PosixFileAttributeView.
defaultOwner	UserPrincipal or String	null/unset	Override the default owner for entries in the Zip file system. The value can be a UserPrincipal or a String value that is used as the UserPrincipal's name.
defaultGroup	GroupPrincipal or String	null/unset	Override the default group for entries in the Zip file system. The value can be a GroupPrincipal or a String value that is used as the GroupPrincipal's name.
defaultPermissions	Set<PosixFilePermission> or String	null/unset	Override the default Set of permissions for entries in the Zip file system. The value can be a Set<PosixFilePermission> or a String that is parsed by PosixFilePermissions::fromString
compressionMethod	String	"DEFLATED"	The value representing the compression method to use when writing entries to the Zip file system. If the value is "STORED", the Zip file system provider will not compress entries when writing to the Zip file system. If the value is "DEFLATED" or the property is not set, the Zip file system provider will use data compression when writing entries to the Zip file system. If the value is not "STORED" or "DEFLATED", an IllegalArgumentException will be thrown when the Zip filesystem is created.
releaseVersion	String or Integer	null/unset	A value representing the version entry to use when accessing a multi-release JAR. If the JAR is not a multi-release JAR, the value will be ignored and the JAR will be considered un-versioned. The value must be either the string "runtime" or represent a valid Java SE Platform version number, such as 9 or 14, in order to determine the version entry. If the value is null or the property is not set, then the JAR will be treated as an un-versioned JAR. If the value is "runtime", the version entry will be determined by invoking Runtime.Version.feature(). If the value does not represent a valid Java SE Platform version number, an IllegalArgumentException will be thrown.

Examples:

Construct a new Zip file system that is identified by a URI. If the Zip file does not exist, it will be created:

 

     URI uri = URI.create("jar:file:/home/luckydog/tennisTeam.zip");
     Map<String, String> env = Map.of("create", "true");
     FileSystem zipfs = FileSystems.newFileSystem(uri, env);
 
 

Construct a new Zip file system that is identified by specifying a path and using automatic file type detection. Iterate from the root of the JAR displaying each found entry:

 

     FileSystem zipfs = FileSystems.newFileSystem(Path.of("helloworld.jar"));
     Path rootDir = zipfs.getPath("/");
     Files.walk(rootDir)
            .forEach(System.out::println);