Module java.base
Package java.io

Class ObjectInputStream

java.lang.Object
java.io.InputStream
java.io.ObjectInputStream
All Implemented Interfaces:
Closeable, DataInput, ObjectInput, ObjectStreamConstants, AutoCloseable
public class ObjectInputStream extends InputStream implements ObjectInput, ObjectStreamConstants
An ObjectInputStream deserializes primitive data and objects previously written using an ObjectOutputStream.

Warning: Deserialization of untrusted data is inherently dangerous and should be avoided. Untrusted data should be carefully validated according to the "Serialization and Deserialization" section of the Secure Coding Guidelines for Java SE. Serialization Filtering describes best practices for defensive use of serial filters.

ObjectOutputStream and ObjectInputStream can provide an application with persistent storage for graphs of objects when used with a FileOutputStream and FileInputStream respectively. ObjectInputStream is used to recover those objects previously serialized. Other uses include passing objects between hosts using a socket stream or for marshaling and unmarshaling arguments and parameters in a remote communication system.

ObjectInputStream ensures that the types of all objects in the graph created from the stream match the classes present in the Java Virtual Machine. Classes are loaded as required using the standard mechanisms.

Only objects that support the java.io.Serializable or java.io.Externalizable interface can be read from streams.

The method readObject is used to read an object from the stream. Java's safe casting should be used to get the desired type. In Java, strings and arrays are objects and are treated as objects during serialization. When read they need to be cast to the expected type.

Primitive data types can be read from the stream using the appropriate method on DataInput.

The default deserialization mechanism for objects restores the contents of each field to the value and type it had when it was written. Fields declared as transient or static are ignored by the deserialization process. References to other objects cause those objects to be read from the stream as necessary. Graphs of objects are restored correctly using a reference sharing mechanism. New objects are always allocated when deserializing, which prevents existing objects from being overwritten.

Reading an object is analogous to running the constructors of a new object. Memory is allocated for the object and initialized to zero (NULL). No-arg constructors are invoked for the non-serializable classes and then the fields of the serializable classes are restored from the stream starting with the serializable class closest to java.lang.object and finishing with the object's most specific class.

For example to read from a stream as written by the example in ObjectOutputStream: 

      FileInputStream fis = new FileInputStream("t.tmp");
      ObjectInputStream ois = new ObjectInputStream(fis);

      int i = ois.readInt();
      String today = (String) ois.readObject();
      Date date = (Date) ois.readObject();

      ois.close();

Classes control how they are serialized by implementing either the java.io.Serializable or java.io.Externalizable interfaces.

Implementing the Serializable interface allows object serialization to save and restore the entire state of the object and it allows classes to evolve between the time the stream is written and the time it is read. It automatically traverses references between objects, saving and restoring entire graphs.

Serializable classes that require special handling during the serialization and deserialization process should implement the following methods: 

 private void writeObject(java.io.ObjectOutputStream stream)
     throws IOException;
 private void readObject(java.io.ObjectInputStream stream)
     throws IOException, ClassNotFoundException;
 private void readObjectNoData()
     throws ObjectStreamException;

The readObject method is responsible for reading and restoring the state of the object for its particular class using data written to the stream by the corresponding writeObject method. The method does not need to concern itself with the state belonging to its superclasses or subclasses. State is restored by reading data from the ObjectInputStream for the individual fields and making assignments to the appropriate fields of the object. Reading primitive data types is supported by DataInput.

Any attempt to read object data which exceeds the boundaries of the custom data written by the corresponding writeObject method will cause an OptionalDataException to be thrown with an eof field value of true. Non-object reads which exceed the end of the allotted data will reflect the end of data in the same way that they would indicate the end of the stream: bytewise reads will return -1 as the byte read or number of bytes read, and primitive reads will throw EOFExceptions. If there is no corresponding writeObject method, then the end of default serialized data marks the end of the allotted data.

Primitive and object read calls issued from within a readExternal method behave in the same manner--if the stream is already positioned at the end of data written by the corresponding writeExternal method, object reads will throw OptionalDataExceptions with eof set to true, bytewise reads will return -1, and primitive reads will throw EOFExceptions. Note that this behavior does not hold for streams written with the old ObjectStreamConstants.PROTOCOL_VERSION_1 protocol, in which the end of data written by writeExternal methods is not demarcated, and hence cannot be detected.

The readObjectNoData method is responsible for initializing the state of the object for its particular class in the event that the serialization stream does not list the given class as a superclass of the object being deserialized. This may occur in cases where the receiving party uses a different version of the deserialized instance's class than the sending party, and the receiver's version extends classes that are not extended by the sender's version. This may also occur if the serialization stream has been tampered; hence, readObjectNoData is useful for initializing deserialized objects properly despite a "hostile" or incomplete source stream.

Serialization does not read or assign values to the fields of any object that does not implement the java.io.Serializable interface. Subclasses of Objects that are not serializable can be serializable. In this case the non-serializable class must have a no-arg constructor to allow its fields to be initialized. In this case it is the responsibility of the subclass to save and restore the state of the non-serializable class. It is frequently the case that the fields of that class are accessible (public, package, or protected) or that there are get and set methods that can be used to restore the state.

The contents of the stream can be filtered during deserialization. If a filter is set on an ObjectInputStream, the ObjectInputFilter can check that the classes, array lengths, number of references in the stream, depth, and number of bytes consumed from the input stream are allowed and if not, can terminate deserialization. A system-wide filter can be configured that is applied to each ObjectInputStream unless replaced using setObjectInputFilter.

Any exception that occurs while deserializing an object will be caught by the ObjectInputStream and abort the reading process.

Implementing the Externalizable interface allows the object to assume complete control over the contents and format of the object's serialized form. The methods of the Externalizable interface, writeExternal and readExternal, are called to save and restore the objects state. When implemented by a class they can write and read their own state using all of the methods of ObjectOutput and ObjectInput. It is the responsibility of the objects to handle any versioning that occurs.

Enum constants are deserialized differently than ordinary serializable or externalizable objects. The serialized form of an enum constant consists solely of its name; field values of the constant are not transmitted. To deserialize an enum constant, ObjectInputStream reads the constant name from the stream; the deserialized constant is then obtained by calling the static method Enum.valueOf(Class, String) with the enum constant's base type and the received constant name as arguments. Like other serializable or externalizable objects, enum constants can function as the targets of back references appearing subsequently in the serialization stream. The process by which enum constants are deserialized cannot be customized: any class-specific readObject, readObjectNoData, and readResolve methods defined by enum types are ignored during deserialization. Similarly, any serialPersistentFields or serialVersionUID field declarations are also ignored--all enum types have a fixed serialVersionUID of 0L.

Records are serialized differently than ordinary serializable or externalizable objects. During deserialization the record's canonical constructor is invoked to construct the record object. Certain serialization-related methods, such as readObject and writeObject, are ignored for serializable records. See Java Object Serialization Specification, Section 1.13, "Serialization of Records" for additional information.

Since:
1.1
See Also:
DataInput, ObjectOutputStream, Serializable, Java Object Serialization Specification, Section 3, "Object Input Classes"

  • Constructor Details

    • ObjectInputStream

      public ObjectInputStream​(InputStream in) throws IOException
      Creates an ObjectInputStream that reads from the specified InputStream. A serialization stream header is read from the stream and verified. This constructor will block until the corresponding ObjectOutputStream has written and flushed the header.

      The serialization filter is initialized to the value of the system-wide filter.

      If a security manager is installed, this constructor will check for the "enableSubclassImplementation" SerializablePermission when invoked directly or indirectly by the constructor of a subclass which overrides the ObjectInputStream.readFields or ObjectInputStream.readUnshared methods.

      Parameters:
      in - input stream to read from
      Throws:
      StreamCorruptedException - if the stream header is incorrect
      IOException - if an I/O error occurs while reading stream header
      SecurityException - if untrusted subclass illegally overrides security-sensitive methods
      NullPointerException - if in is null
      See Also:
      ObjectInputStream(), readFields(), ObjectOutputStream(OutputStream)

    • ObjectInputStream

      protected ObjectInputStream() throws IOException, SecurityException
      Provide a way for subclasses that are completely reimplementing ObjectInputStream to not have to allocate private data just used by this implementation of ObjectInputStream.

      The serialization filter is initialized to the value of the system-wide filter.

      If there is a security manager installed, this method first calls the security manager's checkPermission method with the SerializablePermission("enableSubclassImplementation") permission to ensure it's ok to enable subclassing.

      Throws:
      SecurityException - if a security manager exists and its checkPermission method denies enabling subclassing.
      IOException - if an I/O error occurs while creating this stream
      See Also:
      SecurityManager.checkPermission(java.security.Permission), SerializablePermission

  • Method Details

    • readObject

      public final Object readObject() throws IOException, ClassNotFoundException
      Read an object from the ObjectInputStream. The class of the object, the signature of the class, and the values of the non-transient and non-static fields of the class and all of its supertypes are read. Default deserializing for a class can be overridden using the writeObject and readObject methods. Objects referenced by this object are read transitively so that a complete equivalent graph of objects is reconstructed by readObject.

      The root object is completely restored when all of its fields and the objects it references are completely restored. At this point the object validation callbacks are executed in order based on their registered priorities. The callbacks are registered by objects (in the readObject special methods) as they are individually restored.

      The serialization filter, when not null, is invoked for each object (regular or class) read to reconstruct the root object. See setObjectInputFilter for details.

      Exceptions are thrown for problems with the InputStream and for classes that should not be deserialized. All exceptions are fatal to the InputStream and leave it in an indeterminate state; it is up to the caller to ignore or recover the stream state.

      Specified by:
      readObject in interface ObjectInput
      Returns:
      the object read from the stream
      Throws:
      ClassNotFoundException - Class of a serialized object cannot be found.
      InvalidClassException - Something is wrong with a class used by serialization.
      StreamCorruptedException - Control information in the stream is inconsistent.
      OptionalDataException - Primitive data was found in the stream instead of objects.
      IOException - Any of the usual Input/Output related exceptions.

    • readObjectOverride

      protected Object readObjectOverride() throws IOException, ClassNotFoundException
      This method is called by trusted subclasses of ObjectInputStream that constructed ObjectInputStream using the protected no-arg constructor. The subclass is expected to provide an override method with the modifier "final".
      Returns:
      the Object read from the stream.
      Throws:
      ClassNotFoundException - Class definition of a serialized object cannot be found.
      OptionalDataException - Primitive data was found in the stream instead of objects.
      IOException - if I/O errors occurred while reading from the underlying stream
      Since:
      1.2
      See Also:
      ObjectInputStream(), readObject()

    • readUnshared

      public Object readUnshared() throws IOException, ClassNotFoundException
      Reads an "unshared" object from the ObjectInputStream. This method is identical to readObject, except that it prevents subsequent calls to readObject and readUnshared from returning additional references to the deserialized instance obtained via this call. Specifically:
      • If readUnshared is called to deserialize a back-reference (the stream representation of an object which has been written previously to the stream), an ObjectStreamException will be thrown.
      • If readUnshared returns successfully, then any subsequent attempts to deserialize back-references to the stream handle deserialized by readUnshared will cause an ObjectStreamException to be thrown.
      Deserializing an object via readUnshared invalidates the stream handle associated with the returned object. Note that this in itself does not always guarantee that the reference returned by readUnshared is unique; the deserialized object may define a readResolve method which returns an object visible to other parties, or readUnshared may return a Class object or enum constant obtainable elsewhere in the stream or through external means. If the deserialized object defines a readResolve method and the invocation of that method returns an array, then readUnshared returns a shallow clone of that array; this guarantees that the returned array object is unique and cannot be obtained a second time from an invocation of readObject or readUnshared on the ObjectInputStream, even if the underlying data stream has been manipulated.

      The serialization filter, when not null, is invoked for each object (regular or class) read to reconstruct the root object. See setObjectInputFilter for details.

      ObjectInputStream subclasses which override this method can only be constructed in security contexts possessing the "enableSubclassImplementation" SerializablePermission; any attempt to instantiate such a subclass without this permission will cause a SecurityException to be thrown.

      Returns:
      reference to deserialized object
      Throws:
      ClassNotFoundException - if class of an object to deserialize cannot be found
      StreamCorruptedException - if control information in the stream is inconsistent
      ObjectStreamException - if object to deserialize has already appeared in stream
      OptionalDataException - if primitive data is next in stream
      IOException - if an I/O error occurs during deserialization
      Since:
      1.4

    • defaultReadObject

      public void defaultReadObject() throws IOException, ClassNotFoundException
      Read the non-static and non-transient fields of the current class from this stream. This may only be called from the readObject method of the class being deserialized. It will throw the NotActiveException if it is called otherwise.
      Throws:
      ClassNotFoundException - if the class of a serialized object could not be found.
      IOException - if an I/O error occurs.
      NotActiveException - if the stream is not currently reading objects.

    • readFields

      public ObjectInputStream.GetField readFields() throws IOException, ClassNotFoundException
      Reads the persistent fields from the stream and makes them available by name.
      Returns:
      the GetField object representing the persistent fields of the object being deserialized
      Throws:
      ClassNotFoundException - if the class of a serialized object could not be found.
      IOException - if an I/O error occurs.
      NotActiveException - if the stream is not currently reading objects.
      Since:
      1.2

    • registerValidation

      public void registerValidation​(ObjectInputValidation obj, int prio) throws NotActiveException, InvalidObjectException
      Register an object to be validated before the graph is returned. While similar to resolveObject these validations are called after the entire graph has been reconstituted. Typically, a readObject method will register the object with the stream so that when all of the objects are restored a final set of validations can be performed.
      Parameters:
      obj - the object to receive the validation callback.
      prio - controls the order of callbacks;zero is a good default. Use higher numbers to be called back earlier, lower numbers for later callbacks. Within a priority, callbacks are processed in no particular order.
      Throws:
      NotActiveException - The stream is not currently reading objects so it is invalid to register a callback.
      InvalidObjectException - The validation object is null.

    • resolveClass

      protected Class<?> resolveClass​(ObjectStreamClass desc) throws IOException, ClassNotFoundException
      Load the local class equivalent of the specified stream class description. Subclasses may implement this method to allow classes to be fetched from an alternate source.

      The corresponding method in ObjectOutputStream is annotateClass. This method will be invoked only once for each unique class in the stream. This method can be implemented by subclasses to use an alternate loading mechanism but must return a Class object. Once returned, if the class is not an array class, its serialVersionUID is compared to the serialVersionUID of the serialized class, and if there is a mismatch, the deserialization fails and an InvalidClassException is thrown.

      The default implementation of this method in ObjectInputStream returns the result of calling 

           Class.forName(desc.getName(), false, loader)
      where loader is the first class loader on the current thread's stack (starting from the currently executing method) that is neither the platform class loader nor its ancestor; otherwise, loader is the platform class loader. If this call results in a ClassNotFoundException and the name of the passed ObjectStreamClass instance is the Java language keyword for a primitive type or void, then the Class object representing that primitive type or void will be returned (e.g., an ObjectStreamClass with the name "int" will be resolved to Integer.TYPE). Otherwise, the ClassNotFoundException will be thrown to the caller of this method.
      Parameters:
      desc - an instance of class ObjectStreamClass
      Returns:
      a Class object corresponding to desc
      Throws:
      IOException - any of the usual Input/Output exceptions.
      ClassNotFoundException - if class of a serialized object cannot be found.

    • resolveProxyClass

      protected Class<?> resolveProxyClass​(String[] interfaces) throws IOException, ClassNotFoundException
      Returns a proxy class that implements the interfaces named in a proxy class descriptor; subclasses may implement this method to read custom data from the stream along with the descriptors for dynamic proxy classes, allowing them to use an alternate loading mechanism for the interfaces and the proxy class.

      This method is called exactly once for each unique proxy class descriptor in the stream.

      The corresponding method in ObjectOutputStream is annotateProxyClass. For a given subclass of ObjectInputStream that overrides this method, the annotateProxyClass method in the corresponding subclass of ObjectOutputStream must write any data or objects read by this method.

      The default implementation of this method in ObjectInputStream returns the result of calling Proxy.getProxyClass with the list of Class objects for the interfaces that are named in the interfaces parameter. The Class object for each interface name i is the value returned by calling 

           Class.forName(i, false, loader)
      where loader is the first class loader on the current thread's stack (starting from the currently executing method) that is neither the platform class loader nor its ancestor; otherwise, loader is the platform class loader. Unless any of the resolved interfaces are non-public, this same value of loader is also the class loader passed to Proxy.getProxyClass; if non-public interfaces are present, their class loader is passed instead (if more than one non-public interface class loader is encountered, an IllegalAccessError is thrown). If Proxy.getProxyClass throws an IllegalArgumentException, resolveProxyClass will throw a ClassNotFoundException containing the IllegalArgumentException.
      Parameters:
      interfaces - the list of interface names that were deserialized in the proxy class descriptor
      Returns:
      a proxy class for the specified interfaces
      Throws:
      IOException - any exception thrown by the underlying InputStream
      ClassNotFoundException - if the proxy class or any of the named interfaces could not be found
      Since:
      1.3
      See Also:
      ObjectOutputStream.annotateProxyClass(Class)

    • resolveObject

      protected Object resolveObject​(Object obj) throws IOException
      This method will allow trusted subclasses of ObjectInputStream to substitute one object for another during deserialization. Replacing objects is disabled until enableResolveObject is called. The enableResolveObject method checks that the stream requesting to resolve object can be trusted. Every reference to serializable objects is passed to resolveObject. To insure that the private state of objects is not unintentionally exposed only trusted streams may use resolveObject.

      This method is called after an object has been read but before it is returned from readObject. The default resolveObject method just returns the same object.

      When a subclass is replacing objects it must insure that the substituted object is compatible with every field where the reference will be stored. Objects whose type is not a subclass of the type of the field or array element abort the serialization by raising an exception and the object is not be stored.

      This method is called only once when each object is first encountered. All subsequent references to the object will be redirected to the new object.

      Parameters:
      obj - object to be substituted
      Returns:
      the substituted object
      Throws:
      IOException - Any of the usual Input/Output exceptions.

    • enableResolveObject

      protected boolean enableResolveObject​(boolean enable) throws SecurityException
      Enables the stream to do replacement of objects read from the stream. When enabled, the resolveObject(java.lang.Object) method is called for every object being deserialized.

      If object replacement is currently not enabled, and enable is true, and there is a security manager installed, this method first calls the security manager's checkPermission method with the SerializablePermission("enableSubstitution") permission to ensure that the caller is permitted to enable the stream to do replacement of objects read from the stream.

      Parameters:
      enable - true for enabling use of resolveObject for every object being deserialized
      Returns:
      the previous setting before this method was invoked
      Throws:
      SecurityException - if a security manager exists and its checkPermission method denies enabling the stream to do replacement of objects read from the stream.
      See Also:
      SecurityManager.checkPermission(java.security.Permission), SerializablePermission

    • readStreamHeader

      protected void readStreamHeader() throws IOException, StreamCorruptedException
      The readStreamHeader method is provided to allow subclasses to read and verify their own stream headers. It reads and verifies the magic number and version number.
      Throws:
      IOException - if there are I/O errors while reading from the underlying InputStream
      StreamCorruptedException - if control information in the stream is inconsistent

    • readClassDescriptor

      protected ObjectStreamClass readClassDescriptor() throws IOException, ClassNotFoundException
      Read a class descriptor from the serialization stream. This method is called when the ObjectInputStream expects a class descriptor as the next item in the serialization stream. Subclasses of ObjectInputStream may override this method to read in class descriptors that have been written in non-standard formats (by subclasses of ObjectOutputStream which have overridden the writeClassDescriptor method). By default, this method reads class descriptors according to the format defined in the Object Serialization specification.
      Returns:
      the class descriptor read
      Throws:
      IOException - If an I/O error has occurred.
      ClassNotFoundException - If the Class of a serialized object used in the class descriptor representation cannot be found
      Since:
      1.3
      See Also:
      ObjectOutputStream.writeClassDescriptor(java.io.ObjectStreamClass)

    • read

      public int read() throws IOException
      Reads a byte of data. This method will block if no input is available.
      Specified by:
      read in interface ObjectInput
      Specified by:
      read in class InputStream
      Returns:
      the byte read, or -1 if the end of the stream is reached.
      Throws:
      IOException - If an I/O error has occurred.

    • read

      public int read​(byte[] buf, int off, int len) throws IOException
      Reads into an array of bytes. This method will block until some input is available. Consider using java.io.DataInputStream.readFully to read exactly 'length' bytes.
      Specified by:
      read in interface ObjectInput
      Overrides:
      read in class InputStream
      Parameters:
      buf - the buffer into which the data is read
      off - the start offset in the destination array buf
      len - the maximum number of bytes read
      Returns:
      the actual number of bytes read, -1 is returned when the end of the stream is reached.
      Throws:
      NullPointerException - if buf is null.
      IndexOutOfBoundsException - if off is negative, len is negative, or len is greater than buf.length - off.
      IOException - If an I/O error has occurred.
      See Also:
      DataInputStream.readFully(byte[],int,int)

    • available

      public int available() throws IOException
      Returns the number of bytes that can be read without blocking.
      Specified by:
      available in interface ObjectInput
      Overrides:
      available in class InputStream
      Returns:
      the number of available bytes.
      Throws:
      IOException - if there are I/O errors while reading from the underlying InputStream

    • close

      public void close() throws IOException
      Closes the input stream. Must be called to release any resources associated with the stream.
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Specified by:
      close in interface ObjectInput
      Overrides:
      close in class InputStream
      Throws:
      IOException - If an I/O error has occurred.

    • readBoolean

      public boolean readBoolean() throws IOException
      Reads in a boolean.
      Specified by:
      readBoolean in interface DataInput
      Returns:
      the boolean read.
      Throws:
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • readByte

      public byte readByte() throws IOException
      Reads an 8 bit byte.
      Specified by:
      readByte in interface DataInput
      Returns:
      the 8 bit byte read.
      Throws:
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • readUnsignedByte

      public int readUnsignedByte() throws IOException
      Reads an unsigned 8 bit byte.
      Specified by:
      readUnsignedByte in interface DataInput
      Returns:
      the 8 bit byte read.
      Throws:
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • readChar

      public char readChar() throws IOException
      Reads a 16 bit char.
      Specified by:
      readChar in interface DataInput
      Returns:
      the 16 bit char read.
      Throws:
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • readShort

      public short readShort() throws IOException
      Reads a 16 bit short.
      Specified by:
      readShort in interface DataInput
      Returns:
      the 16 bit short read.
      Throws:
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • readUnsignedShort

      public int readUnsignedShort() throws IOException
      Reads an unsigned 16 bit short.
      Specified by:
      readUnsignedShort in interface DataInput
      Returns:
      the 16 bit short read.
      Throws:
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • readInt

      public int readInt() throws IOException
      Reads a 32 bit int.
      Specified by:
      readInt in interface DataInput
      Returns:
      the 32 bit integer read.
      Throws:
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • readLong

      public long readLong() throws IOException
      Reads a 64 bit long.
      Specified by:
      readLong in interface DataInput
      Returns:
      the read 64 bit long.
      Throws:
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • readFloat

      public float readFloat() throws IOException
      Reads a 32 bit float.
      Specified by:
      readFloat in interface DataInput
      Returns:
      the 32 bit float read.
      Throws:
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • readDouble

      public double readDouble() throws IOException
      Reads a 64 bit double.
      Specified by:
      readDouble in interface DataInput
      Returns:
      the 64 bit double read.
      Throws:
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • readFully

      public void readFully​(byte[] buf) throws IOException
      Reads bytes, blocking until all bytes are read.
      Specified by:
      readFully in interface DataInput
      Parameters:
      buf - the buffer into which the data is read
      Throws:
      NullPointerException - If buf is null.
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • readFully

      public void readFully​(byte[] buf, int off, int len) throws IOException
      Reads bytes, blocking until all bytes are read.
      Specified by:
      readFully in interface DataInput
      Parameters:
      buf - the buffer into which the data is read
      off - the start offset into the data array buf
      len - the maximum number of bytes to read
      Throws:
      NullPointerException - If buf is null.
      IndexOutOfBoundsException - If off is negative, len is negative, or len is greater than buf.length - off.
      EOFException - If end of file is reached.
      IOException - If other I/O error has occurred.

    • skipBytes

      public int skipBytes​(int len) throws IOException
      Skips bytes.
      Specified by:
      skipBytes in interface DataInput
      Parameters:
      len - the number of bytes to be skipped
      Returns:
      the actual number of bytes skipped.
      Throws:
      IOException - If an I/O error has occurred.

    • readLine

      @Deprecated public String readLine() throws IOException
      Deprecated.
      This method does not properly convert bytes to characters. see DataInputStream for the details and alternatives.
      Reads in a line that has been terminated by a \n, \r, \r\n or EOF.
      Specified by:
      readLine in interface DataInput
      Returns:
      a String copy of the line.
      Throws:
      IOException - if there are I/O errors while reading from the underlying InputStream

    • readUTF

      public String readUTF() throws IOException
      Reads a String in modified UTF-8 format.
      Specified by:
      readUTF in interface DataInput
      Returns:
      the String.
      Throws:
      IOException - if there are I/O errors while reading from the underlying InputStream
      UTFDataFormatException - if read bytes do not represent a valid modified UTF-8 encoding of a string

    • getObjectInputFilter

      public final ObjectInputFilter getObjectInputFilter()
      Returns the serialization filter for this stream. The serialization filter is the most recent filter set in setObjectInputFilter or the initial system-wide filter from ObjectInputFilter.Config.getSerialFilter.
      Returns:
      the serialization filter for the stream; may be null
      Since:
      9

    • setObjectInputFilter

      public final void setObjectInputFilter​(ObjectInputFilter filter)
      Set the serialization filter for the stream. The filter's checkInput method is called for each class and reference in the stream. The filter can check any or all of the class, the array length, the number of references, the depth of the graph, and the size of the input stream. The depth is the number of nested readObject calls starting with the reading of the root of the graph being deserialized and the current object being deserialized. The number of references is the cumulative number of objects and references to objects already read from the stream including the current object being read. The filter is invoked only when reading objects from the stream and for not primitives.

      If the filter returns Status.REJECTED, null or throws a RuntimeException, the active readObject or readUnshared throws InvalidClassException, otherwise deserialization continues uninterrupted.

      The serialization filter is initialized to the value of ObjectInputFilter.Config.getSerialFilter when the ObjectInputStream is constructed and can be set to a custom filter only once. The filter must be set before reading any objects from the stream; for example, by calling readObject() or readUnshared().

      Implementation Requirements:
      The filter, when not null, is invoked during readObject and readUnshared for each object (regular or class) in the stream. Strings are treated as primitives and do not invoke the filter. The filter is called for:
      • each object reference previously deserialized from the stream (class is null, arrayLength is -1),
      • each regular class (class is not null, arrayLength is -1),
      • each interface of a dynamic proxy and the dynamic proxy class itself (class is not null, arrayLength is -1),
      • each array is filtered using the array type and length of the array (class is the array type, arrayLength is the requested length),
      • each object replaced by its class' readResolve method is filtered using the replacement object's class, if not null, and if it is an array, the arrayLength, otherwise -1,
      • and each object replaced by resolveObject is filtered using the replacement object's class, if not null, and if it is an array, the arrayLength, otherwise -1.
      When the checkInput method is invoked it is given access to the current class, the array length, the current number of references already read from the stream, the depth of nested calls to readObject or readUnshared, and the implementation dependent number of bytes consumed from the input stream.

      Each call to readObject or readUnshared increases the depth by 1 before reading an object and decreases by 1 before returning normally or exceptionally. The depth starts at 1 and increases for each nested object and decrements when each nested call returns. The count of references in the stream starts at 1 and is increased before reading an object.

      Parameters:
      filter - the filter, may be null
      Throws:
      SecurityException - if there is security manager and the SerializablePermission("serialFilter") is not granted
      IllegalStateException - if the current filter is not null and is not the system-wide filter, or if an object has been read
      Since:
      9