com.google.apphosting.vmruntime

Class VmMetadataCache

java.lang.Object

com.google.apphosting.vmruntime.VmMetadataCache

public class VmMetadataCache
extends Object

A class to retrieve and cache the meta-data of a VM running in Google's Compute Engine.

Field Summary

Fields

Modifier and Type	Field and Description
static String	DEFAULT_META_DATA_SERVER The meta-data server's URL prefix.
static String	META_DATA_PATTERN

Constructor Summary

Constructors

Constructor and Description
VmMetadataCache()

Method Summary

Modifier and Type	Method and Description
String	getMetadata(String path) Returns the value of the VM's meta-data attribute, or null if retrieval has failed.
protected String	getMetadataFromServer(String path) Retrieves the specified path from the VM's meta-data server.
protected HttpURLConnection	openConnection(String path) Returns an HTTP URL connection to read the value of the specified attribute.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_META_DATA_SERVER

public static final String DEFAULT_META_DATA_SERVER

The meta-data server's URL prefix.

See Also:

Constant Field Values

META_DATA_PATTERN

public static final String META_DATA_PATTERN

See Also:

Constant Field Values

Constructor Detail

VmMetadataCache

public VmMetadataCache()

Method Detail

getMetadata

public String getMetadata(String path)

Returns the value of the VM's meta-data attribute, or null if retrieval has failed.

Parameters:

path - the meta-data attribute to be retrieved (e.g. "image", "attributes/sshKeys").

Returns:

the attribute's string value or null if retrieval has failed.

openConnection

protected HttpURLConnection openConnection(String path)
                                    throws IOException

Returns an HTTP URL connection to read the value of the specified attribute.

May be overridden in tests.

Parameters:

path - the meta-data attribute to be retrieved (e.g. "image", "attributes/sshKeys").

Returns:

the HTTP URL connection object.

Throws:

IOException - if the connection could not be opened.

getMetadataFromServer

protected String getMetadataFromServer(String path)
                                throws IOException

Retrieves the specified path from the VM's meta-data server.

Parameters:

path - a path in the meta-data server (e.g. "image").

Returns:

the meta-data's string value or null if the attribute is not found.

Throws:

IOException - if the connection to the meta-data server fails, or refused.