Java沙箱 - MaxCompute

MaxCompute MapReduce及UDF程式在分布式環境中運行時，受到Java沙箱的限制（MapReduce作業的主程式，例如MapReduce Main則不受此限制）。

Java沙箱限制說明

不允許直接存取本地檔案，只能通過MaxCompute MapReduce、Graph提供的介面間接訪問。包括：
- Resources選項指定的資源，包括檔案、Jar包和資源表等。
- 通過System.out和System.err輸出日誌資訊。可以通過MaxCompute用戶端的Log命令查看日誌資訊。
不允許直接存取Distributed File System，只能通過MaxCompute MapReduce、Graph訪問表的記錄。
不允許JNI調用限制。
不允許建立Java線程，不允許啟動子進程執行Linux命令。
不允許訪問網路，包括擷取本地IP地址等。
Java反射限制：suppressAccessChecks許可權被禁止，無法setAccessible某個私人的屬性或方法，以達到讀取私人屬性或調用私人方法的目的。

訪問本地檔案限制

在代碼中，直接使用下列方法訪問本地檔案會報access denied異常：

java.io.File

public boolean delete()
public void deleteOnExit()
public boolean exists()
public boolean canRead()
public boolean isFile()
public boolean isDirectory()
public boolean isHidden()
public long lastModified()
public long length()
public String[] list()
public String[] list(FilenameFilter filter)
public File[] listFiles()
public File[] listFiles(FilenameFilter filter)
public File[] listFiles(FileFilter filter)
public boolean canWrite()
public boolean createNewFile()
public static File createTempFile(String prefix, String suffix)
public static File createTempFile(String prefix,  String suffix,File directory)
public boolean mkdir()
public boolean mkdirs()
public boolean renameTo(File dest)
public boolean setLastModified(long time)
public boolean setReadOnly()

java.io.RandomAccessFile

RandomAccessFile(String name, String mode)
RandomAccessFile(File file, String mode)

java.io.FileInputStream

FileInputStream(FileDescriptor fdObj)
FileInputStream(String name)
FileInputStream(File file)

java.io.FileOutputStream

FileOutputStream(FileDescriptor fdObj)
FileOutputStream(File file)
FileOutputStream(String name)
FileOutputStream(String name, boolean append)

java.lang.Class

public ProtectionDomain getProtectionDomain()

java.lang.ClassLoader

ClassLoader()
ClassLoader(ClassLoader parent)

java.lang.Runtime

public Process exec(String command)
public Process exec(String command, String envp[])
public Process exec(String cmdarray[])
public Process exec(String cmdarray[], String envp[])
public void exit(int status)
public static void runFinalizersOnExit(boolean value)
public void addShutdownHook(Thread hook)
public boolean removeShutdownHook(Thread hook)
public void load(String lib)
public void loadLibrary(String lib)

java.lang.System

public static void exit(int status)
public static void runFinalizersOnExit(boolean value)
public static void load(String filename)
public static void loadLibrary( String libname)
public static Properties getProperties()
public static void setProperties(Properties props)
public static String getProperty(String key) // 只允許部分key可以訪問
public static String getProperty(String key, String def) // 只允許部分key可以訪問
public static String setProperty(String key, String value)
public static void setIn(InputStream in)
public static void setOut(PrintStream out)
public static void setErr(PrintStream err)
public static synchronized void setSecurityManager(SecurityManager s)

System.getProperty允許的key列表如下。

java.version
java.vendor
java.vendor.url
java.class.version
os.name
os.version
os.arch
file.separator
path.separator
line.separator
java.specification.version
java.specification.vendor
java.specification.name
java.vm.specification.version
java.vm.specification.vendor
java.vm.specification.name
java.vm.version
java.vm.vendor
java.vm.name
file.encoding
user.timezone

java.lang.Thread

Thread()
Thread(Runnable target)
Thread(String name)
Thread(Runnable target, String name)
Thread(ThreadGroup group, ...)
public final void checkAccess()
public void interrupt()
public final void suspend()
public final void resume()
public final void setPriority (int newPriority)
public final void setName(String name)
public final void setDaemon(boolean on)
public final void stop()
public final synchronized void stop(Throwable obj)
public static int enumerate(Thread tarray[])
public void setContextClassLoader(ClassLoader cl)

java.lang.ThreadGroup

ThreadGroup(String name)
ThreadGroup(ThreadGroup parent, String name)
public final void checkAccess()
public int enumerate(Thread list[])
public int enumerate(Thread list[], boolean recurse)
public int enumerate(ThreadGroup list[])
public int enumerate(ThreadGroup list[], boolean recurse)
public final ThreadGroup getParent()
public final void setDaemon(boolean daemon)
public final void setMaxPriority(int pri)
public final void suspend()
public final void resume()
public final void destroy()
public final void interrupt()
public final void stop()

java.lang.reflect.AccessibleObject

public static void setAccessible(...)
public void setAccessible(...)

java.net.InetAddress

public String getHostName()
public static InetAddress[] getAllByName(String host)
public static InetAddress getLocalHost()

java.net.DatagramSocket
```
public InetAddress getLocalAddress()
```
java.net.Socket
```
Socket(...)
```

java.net.ServerSocket

ServerSocket(...)
public Socket accept()
protected final void implAccept(Socket s)
public static synchronized void setSocketFactory(...)
public static synchronized void setSocketImplFactory(...)

java.net.DatagramSocket

DatagramSocket(...)
public synchronized void receive(DatagramPacket p)

java.net.MulticastSocket
```
MulticastSocket(...)
```

java.net.URL

URL(...)
public static synchronized void setURLStreamHandlerFactory(...)
java.net.URLConnection
public static synchronized void setContentHandlerFactory(...)
public static void setFileNameMap(FileNameMap map)

java.net.HttpURLConnection

public static void setFollowRedirects(boolean set)
java.net.URLClassLoader
URLClassLoader(...)

java.security.AccessControlContext

public AccessControlContext(AccessControlContext acc, DomainCombiner combiner)
public DomainCombiner getDomainCombiner()