{"id":3465,"date":"2019-06-20T11:46:52","date_gmt":"2019-06-20T11:46:52","guid":{"rendered":"http:\/\/softlect.in\/?p=3465"},"modified":"2019-06-20T12:04:28","modified_gmt":"2019-06-20T12:04:28","slug":"java-input-and-output","status":"publish","type":"post","link":"http:\/\/softlect.com\/index.php\/java-input-and-output\/","title":{"rendered":"Java Input and Output"},"content":{"rendered":"JAVA STREAMS<\/h1>\n
Streams provide the data transfer mechanism on top of sockets. To use a telephone structure, sockets are like the telephone connection and streams are like voice exchanges. When you speak to a friend on the telephone, you create an output stream; your voice is picked up on the receiving end by an input stream in this case, your friend’s ear. You simply write data in one end of a stream and the recipient reads it from the other end. You will find that it is typically easier to write to a stream than to read from it. The writer simply writes to the stream and puts the data in the stream. The reader, on the other hand, must be prepared to deal with slow writers without blocking an entire program waiting for data to arrive. The reader must also be able to detect the end of a stream. The java.io<\/em> package provides a large number of classes most are derived from the InputStream<\/strong> or OutputStream<\/strong> abstract classes. Stream classes are almost always paired there is usually a corresponding output stream for each input stream type. Figure 10-8 shows the stream classes in java.io<\/em>.<\/p>\n <\/p>\n
The Socket<\/strong> class provides two methods that let you associate a socket with a pair of streams; getOutputStream<\/em> and getInputStream.<\/em> The first method returns an OutputStream<\/strong> object, and the second returns an InputStream<\/strong> object. You can then extend these objects to support any of the specialized input\/output stream pairs we show in Figure 10-8.<\/p>\n <\/p>\n
The Java Output Stream Classes<\/p>\n
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Figure 10-9 shows the output stream class hierarchy. All the output stream classes are derived from the OutputStream<\/strong> abstract class. The two important classes are DataOutputStream<\/strong> and BufferedOutputStream. <\/strong>They are both filtering streams derived from FilterOutputStream. <\/strong><\/p>\n <\/p>\n
OutputStream is the abstract class that defines the basic output methods that all output stream classes must provide. You invoke write<\/strong> to write a single byte or an array or subarray of bytes. You invoke flush<\/strong> to force any buffered data to be sent. Finally, you invoke close<\/strong> to close the stream and free up the system resources it owns<\/p>\n\u00a0<\/strong><\/p>\nFilterOutputStream is the class that lets you chain together and filter output streams. The class simply overrides all methods of OutputStream<\/strong> with versions that pass all requests to the underlying output stream. Subclasses of FilterOut\u00adputStream<\/strong> may further override some of these methods as well as provide additional methods and fields.<\/p>\n\u00a0<\/strong><\/p>\n <\/p>\n
DataOutputStream is the class that implements a filtered stream enabling you to write Java primitive data types to an output stream in their binary represen\u00adtations. A recipient application uses a DataInputStream to read the data back into Java. You invoke the constructor DataOutputStream<\/strong> to create a data output stream filter; you must specify the OutputStream object to be filtered. You invoke size<\/strong> to obtain the number of bytes you wrote so far. You invoke write<\/strong> to write a single byte. You can write multiple bytes by specifying an offset within a buffer and the number of bytes to write. The class provides methods for writing all the basic Java types to a stream in their binary representation. These methods are self-explanatory except for writeUTF. You invoke writeUTF<\/strong> to write a Java string of Unicode characters using an ASCII compatible encoding scheme called UTF-8.<\/p>\n\u00a0<\/strong><\/p>\nBufferedOutputStream is the class that implements a buffered output stream filter. Instead of calling the stream for each byte you write, it stores the data in a buffer. It then writes the data to the output stream if the buffer reaches its capacity. You can explicitly flush a buffer’s contents by using flush<\/strong> or close<\/strong>. You invoke the constructor BufferedOutputStream<\/strong> to create a buffered stream filter; you must specify the OutputStream<\/strong> object to be filtered. The constructor provides a 512-byte default buffer that you can optionally override with a size you specify. You invoke write<\/strong> to write a single byte; you can write multiple bytes by specifying an offset within a buffer and the number of bytes to write. A buffered filter gives you better performance; it lets you write<\/strong> data to streams in chunks instead of writing it one byte at a time.<\/p>\n <\/p>\n
Here are the class\u2019s Methods descriptions for OutputStream, FilterOutputStream, DataOutputStream, and the BufferedOutputStream:<\/p>\n
<\/p>\n
\n\n\nClass OutputStream<\/strong><\/td>\n<\/tr>\n\nOutputStream<\/a><\/strong>()<\/td>\n| <\/td>\n<\/tr>\n | \nVoid close<\/a><\/strong>()<\/td>\n| Closes this output stream and releases any system resources associated with this stream.<\/td>\n<\/tr>\n | \nVoid flush<\/a><\/strong>()<\/td>\n| Flushes this output stream and forces any buffered output bytes to be written out.<\/td>\n<\/tr>\n | \nVoid write<\/a><\/strong>(byte[]\u00a0b)<\/td>\n| Writes b.length bytes from the specified byte array to this output stream.<\/td>\n<\/tr>\n | \nVoid write<\/a><\/strong>(byte[]\u00a0b, int\u00a0off, int\u00a0len)<\/td>\n| Writes len bytes from the specified byte array starting at offset off to this output stream.<\/td>\n<\/tr>\n | \nabstract \u00a0void write<\/a><\/strong>(int\u00a0b)<\/td>\n| Writes the specified byte to this output stream.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n <\/p>\n Listing 10-7: The OutputStream Class<\/p>\n \u00a0<\/strong><\/p>\n\u00a0<\/strong><\/p>\n\n\n\nClass FilterOutputStream<\/strong><\/td>\n<\/tr>\n\nFilterOutputStream<\/a><\/strong>(OutputStream<\/a>\u00a0out)<\/td>\n| Creates an output stream filter built on top of the specified underlying output stream.<\/td>\n<\/tr>\n | \nVoid close<\/a><\/strong>()<\/td>\n| Closes this output stream and releases any system resources associated with the stream<\/td>\n<\/tr>\n | \nVoid flush<\/a><\/strong>()<\/td>\n| Flushes this output stream and forces any buffered output bytes to be written out to the stream.<\/td>\n<\/tr>\n | \nVoid write<\/a><\/strong>(byte[]\u00a0b)<\/td>\n| Writes b.length bytes to this output stream.<\/td>\n<\/tr>\n | \nVoid write<\/a><\/strong>(byte[]\u00a0b, int\u00a0off, int\u00a0len)<\/td>\n| Writes len bytes from the specified byte array starting at offset off to this output stream.<\/td>\n<\/tr>\n | \nVoid write<\/a><\/strong>(int\u00a0b)<\/td>\n| Writes the specified byte to this output stream.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \u00a0<\/strong><\/p>\n\u00a0<\/strong><\/p>\nListing 10-8: The FilterOutputStream Class<\/p>\n \u00a0<\/strong><\/p>\n\n\n\nClass DataOutputStream<\/strong><\/td>\n<\/tr>\n\nDataOutputStream<\/a><\/strong>(OutputStream<\/a>\u00a0out)<\/td>\n| Creates a new data output stream to write data to the specified underlying output stream.<\/td>\n<\/tr>\n | \nVoid flush<\/a><\/strong>()<\/td>\n| Flushes this data output stream.<\/td>\n<\/tr>\n | \nInt size<\/a><\/strong>()<\/td>\n| Returns the current value of the counter written, the number of bytes written to this data output stream so far.<\/td>\n<\/tr>\n | \nVoid write<\/a><\/strong>(byte[]\u00a0b, int\u00a0off, int\u00a0len)<\/td>\n| Writes len bytes from the specified byte array starting at offset off to the underlying output stream.<\/td>\n<\/tr>\n | \nVoid write<\/a><\/strong>(int\u00a0b)<\/td>\n| Writes the specified byte (the low eight bits of the argument b) to the underlying output stream.<\/td>\n<\/tr>\n | \nVoid writeBoolean<\/a><\/strong>(boolean\u00a0v)<\/td>\n| Writes a boolean to the underlying output stream as a 1-byte value.<\/td>\n<\/tr>\n | \nVoid writeByte<\/a><\/strong>(int\u00a0v)<\/td>\n| Writes out a byte to the underlying output stream as a 1-byte value.<\/td>\n<\/tr>\n | \nVoid writeBytes<\/a><\/strong>(String<\/a>\u00a0s)<\/td>\n| Writes out the string to the underlying output stream as a sequence of bytes.<\/td>\n<\/tr>\n | \nVoid writeChar<\/a><\/strong>(int\u00a0v)<\/td>\n| Writes a char to the underlying output stream as a 2-byte value, high byte first.<\/td>\n<\/tr>\n | \nVoid writeChars<\/a><\/strong>(String<\/a>\u00a0s)<\/td>\n| Writes a string to the underlying output stream as a sequence of characters.<\/td>\n<\/tr>\n | \nVoid writeDouble<\/a><\/strong>(double\u00a0v)<\/td>\n| Converts the double argument to a long using the doubleToLongBits method in class Double, and then writes that long value to the underlying output stream as an 8-byte quantity, high byte first.<\/td>\n<\/tr>\n | \nVoid writeFloat<\/a><\/strong>(float\u00a0v)<\/td>\n| Converts the float argument to an int using the floatToIntBits method in class Float, and then writes that int value to the underlying output stream as a 4-byte quantity, high byte first.<\/td>\n<\/tr>\n | \nVoid writeInt<\/a><\/strong>(int\u00a0v)<\/td>\n| Writes an int to the underlying output stream as four bytes, high byte first.<\/td>\n<\/tr>\n | \nVoid writeLong<\/a><\/strong>(long\u00a0v)<\/td>\n| Writes a long to the underlying output stream as eight bytes, high byte first.<\/td>\n<\/tr>\n | \nVoid writeShort<\/a><\/strong>(int\u00a0v)<\/td>\n| Writes a short to the underlying output stream as two bytes, high byte first.<\/td>\n<\/tr>\n | \nVoid writeUTF<\/a><\/strong>(String<\/a>\u00a0str)<\/td>\n| Writes a string to the underlying output stream using Java modified UTF-8 encoding in a machine-independent manner.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \u00a0<\/strong><\/p>\nListing 10-9: The DataOutputStream Class<\/p>\n \u00a0<\/strong><\/p>\n\u00a0<\/strong><\/p>\n\n\n\nClass BufferedOutputStream<\/strong><\/td>\n<\/tr>\n\nBufferedOutputStream<\/a><\/strong>(OutputStream<\/a>\u00a0out)<\/td>\n| Creates a new buffered output stream to write data to the specified underlying output stream with a default 512-byte buffer size.<\/td>\n<\/tr>\n | \nBufferedOutputStream<\/a><\/strong>(OutputStream<\/a>\u00a0out, int\u00a0size)<\/td>\n| Creates a new buffered output stream to write data to the specified underlying output stream with the specified buffer size.<\/td>\n<\/tr>\n | \nVoid flush<\/a><\/strong>()<\/td>\n| Flushes this buffered output stream.<\/td>\n<\/tr>\n | \nVoid write<\/a><\/strong>(byte[]\u00a0b, int\u00a0off, int\u00a0len)<\/td>\n| Writes len bytes from the specified byte array starting at offset off to this buffered output stream.<\/td>\n<\/tr>\n | \nVoid write<\/a><\/strong>(int\u00a0b)<\/td>\n| Writes the specified byte to this buffered output stream.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \u00a0<\/strong><\/p>\nListing 10-10: The BufferedOutputStream Class<\/p>\n \u00a0<\/strong><\/p>\nThe Java InputStream Class<\/p>\n \u00a0<\/strong><\/p>\nFigure 10-10 shows the input stream class hierarchy. All the input stream classes are derived from the InputStream<\/strong> abstract class. The two classes that interest us the most are DataInputStream<\/strong> and BufferedInputStream.<\/strong> They are both filtering streams derived from FilterInputStream.<\/strong><\/p>\n <\/p>\n InputStream is the abstract class that defines the basic input methods that all <\/strong>input stream classes must provide. You invoke read<\/strong> to read the next byte from the stream. If you pass read an array, it will fill it as much as possible with data from the stream and then return the number of bytes it actually read. You can <\/strong>also specify an offset to start reading from, as well as the number of bytes you want to read. You invoke available<\/strong> to obtain the number of bytes that are already in the stream. You invoke skip<\/strong> to skip over the next number of bytes within a stream. You invoke mark<\/strong> to mark the current position within a stream; you can specify the number of bytes to be read before the mark position is invalidated. You can subsequently invoke reset<\/strong> to reposition the stream to the marked position. You invoke markSupported<\/strong> to check if the stream supports marking; it will return true if it does. Finally, you invoke close<\/strong> to close the stream and free up the system resources it consumes.<\/p>\n <\/p>\n FilterInputStream is the class that simply overrides all methods of InputStream<\/strong> with versions that pass all requests to the underlying input stream. Subclasses of FilterInputStream<\/strong> may further override some of these methods as well as provide additional methods and fields.<\/p>\n <\/p>\n DataInputStream Is the class that implements a filtered stream that lets you read Java primitive data types from an input stream. You invoke the constructor DataInpntStream<\/strong> to create a data input stream filter; you must specify the InputStream object to be filtered. You invoke read<\/strong> to read a single byte. You can read multiple bytes by specifying a buffer and the number of bytes to read. The method will block until some input is available; it will then return the number of bytes actually read. You invoke readFully<\/strong> to read data into an array of bytes; it will block until all the data is available. The class also provides methods for reading all the basic Java types from a stream in their binary representation. These methods are self-explanatory, except for two readLine and readUTF. The readLine<\/strong> method reads characters from a stream until it encounters a newline or a carriage return. The readUTF<\/strong> method reads a Java string of Unicode text encoded in the UTF-8 format.<\/p>\n <\/p>\n BufferedInputStream is the class that implements a buffered input stream filter. It reads in data and stores it in a buffer. When you request data, it is usually available in the buffer. The idea is to block data fetches and avoid dipping into the stream for each byte you request. You invoke the constructor Buffered\u00adInputStream<\/strong> to create a new buffered input stream filter; you must pass it the InputStream object to be filtered and an optional buffer size the default is 512 bytes. You invoke read<\/strong> to read a single byte, or you can read multiple bytes by specifying an offset within a buffer and the number of bytes to read. Again, the reason we’re doing all this is to improve stream performance by reading in chunks of data instead of reading in one byte at a time.<\/p>\n <\/p>\n <\/p>\n <\/p>\n Here are the class declarations for InputStream, FilterInputStream, DataInputStream<\/strong> and BufferedlnputStream:<\/strong><\/p>\n\u00a0<\/strong><\/p>\n | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |