001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 018 package javax.servlet.jsp; 019 020 import java.io.IOException; 021 022 /** 023 * <p> 024 * The actions and template data in a JSP page is written using the 025 * JspWriter object that is referenced by the implicit variable out which 026 * is initialized automatically using methods in the PageContext object. 027 *<p> 028 * This abstract class emulates some of the functionality found in the 029 * java.io.BufferedWriter and java.io.PrintWriter classes, 030 * however it differs in that it throws java.io.IOException from the print 031 * methods while PrintWriter does not. 032 * <p><B>Buffering</B> 033 * <p> 034 * The initial JspWriter object is associated with the PrintWriter object 035 * of the ServletResponse in a way that depends on whether the page is or 036 * is not buffered. If the page is not buffered, output written to this 037 * JspWriter object will be written through to the PrintWriter directly, 038 * which will be created if necessary by invoking the getWriter() method 039 * on the response object. But if the page is buffered, the PrintWriter 040 * object will not be created until the buffer is flushed and 041 * operations like setContentType() are legal. Since this flexibility 042 * simplifies programming substantially, buffering is the default for JSP 043 * pages. 044 * <p> 045 * Buffering raises the issue of what to do when the buffer is 046 * exceeded. Two approaches can be taken: 047 * <ul> 048 * <li> 049 * Exceeding the buffer is not a fatal error; when the buffer is 050 * exceeded, just flush the output. 051 * <li> 052 * Exceeding the buffer is a fatal error; when the buffer is exceeded, 053 * raise an exception. 054 * </ul> 055 * <p> 056 * Both approaches are valid, and thus both are supported in the JSP 057 * technology. The behavior of a page is controlled by the autoFlush 058 * attribute, which defaults to true. In general, JSP pages that need to 059 * be sure that correct and complete data has been sent to their client 060 * may want to set autoFlush to false, with a typical case being that 061 * where the client is an application itself. On the other hand, JSP 062 * pages that send data that is meaningful even when partially 063 * constructed may want to set autoFlush to true; such as when the 064 * data is sent for immediate display through a browser. Each application 065 * will need to consider their specific needs. 066 * <p> 067 * An alternative considered was to make the buffer size unbounded; but, 068 * this had the disadvantage that runaway computations would consume an 069 * unbounded amount of resources. 070 * <p> 071 * The "out" implicit variable of a JSP implementation class is of this type. 072 * If the page directive selects autoflush="true" then all the I/O operations 073 * on this class shall automatically flush the contents of the buffer if an 074 * overflow condition would result if the current operation were performed 075 * without a flush. If autoflush="false" then all the I/O operations on this 076 * class shall throw an IOException if performing the current operation would 077 * result in a buffer overflow condition. 078 * 079 * @see java.io.Writer 080 * @see java.io.BufferedWriter 081 * @see java.io.PrintWriter 082 */ 083 084 abstract public class JspWriter extends java.io.Writer { 085 086 /** 087 * Constant indicating that the Writer is not buffering output. 088 */ 089 090 public static final int NO_BUFFER = 0; 091 092 /** 093 * Constant indicating that the Writer is buffered and is using the 094 * implementation default buffer size. 095 */ 096 097 public static final int DEFAULT_BUFFER = -1; 098 099 /** 100 * Constant indicating that the Writer is buffered and is unbounded; this 101 * is used in BodyContent. 102 */ 103 104 public static final int UNBOUNDED_BUFFER = -2; 105 106 /** 107 * Protected constructor. 108 * 109 * @param bufferSize the size of the buffer to be used by the JspWriter 110 * @param autoFlush whether the JspWriter should be autoflushing 111 */ 112 113 protected JspWriter(int bufferSize, boolean autoFlush) { 114 this.bufferSize = bufferSize; 115 this.autoFlush = autoFlush; 116 } 117 118 /** 119 * Write a line separator. The line separator string is defined by the 120 * system property <tt>line.separator</tt>, and is not necessarily a single 121 * newline ('\n') character. 122 * 123 * @exception IOException If an I/O error occurs 124 */ 125 126 abstract public void newLine() throws IOException; 127 128 /** 129 * Print a boolean value. The string produced by <code>{@link 130 * java.lang.String#valueOf(boolean)}</code> is written to the 131 * JspWriter's buffer or, if no buffer is used, directly to the 132 * underlying writer. 133 * 134 * @param b The <code>boolean</code> to be printed 135 * @throws java.io.IOException If an error occured while writing 136 */ 137 138 abstract public void print(boolean b) throws IOException; 139 140 /** 141 * Print a character. The character is written to the 142 * JspWriter's buffer or, if no buffer is used, directly to the 143 * underlying writer. 144 * 145 * @param c The <code>char</code> to be printed 146 * @throws java.io.IOException If an error occured while writing 147 */ 148 149 abstract public void print(char c) throws IOException; 150 151 /** 152 * Print an integer. The string produced by <code>{@link 153 * java.lang.String#valueOf(int)}</code> is written to the 154 * JspWriter's buffer or, if no buffer is used, directly to the 155 * underlying writer. 156 * 157 * @param i The <code>int</code> to be printed 158 * @see java.lang.Integer#toString(int) 159 * @throws java.io.IOException If an error occured while writing 160 */ 161 162 abstract public void print(int i) throws IOException; 163 164 /** 165 * Print a long integer. The string produced by <code>{@link 166 * java.lang.String#valueOf(long)}</code> is written to the 167 * JspWriter's buffer or, if no buffer is used, directly to the 168 * underlying writer. 169 * 170 * @param l The <code>long</code> to be printed 171 * @see java.lang.Long#toString(long) 172 * @throws java.io.IOException If an error occured while writing 173 */ 174 175 abstract public void print(long l) throws IOException; 176 177 /** 178 * Print a floating-point number. The string produced by <code>{@link 179 * java.lang.String#valueOf(float)}</code> is written to the 180 * JspWriter's buffer or, if no buffer is used, directly to the 181 * underlying writer. 182 * 183 * @param f The <code>float</code> to be printed 184 * @see java.lang.Float#toString(float) 185 * @throws java.io.IOException If an error occured while writing 186 */ 187 188 abstract public void print(float f) throws IOException; 189 190 /** 191 * Print a double-precision floating-point number. The string produced by 192 * <code>{@link java.lang.String#valueOf(double)}</code> is written to 193 * the JspWriter's buffer or, if no buffer is used, directly to the 194 * underlying writer. 195 * 196 * @param d The <code>double</code> to be printed 197 * @see java.lang.Double#toString(double) 198 * @throws java.io.IOException If an error occured while writing 199 */ 200 201 abstract public void print(double d) throws IOException; 202 203 /** 204 * Print an array of characters. The characters are written to the 205 * JspWriter's buffer or, if no buffer is used, directly to the 206 * underlying writer. 207 * 208 * @param s The array of chars to be printed 209 * 210 * @throws NullPointerException If <code>s</code> is <code>null</code> 211 * @throws java.io.IOException If an error occured while writing 212 */ 213 214 abstract public void print(char s[]) throws IOException; 215 216 /** 217 * Print a string. If the argument is <code>null</code> then the string 218 * <code>"null"</code> is printed. Otherwise, the string's characters are 219 * written to the JspWriter's buffer or, if no buffer is used, directly 220 * to the underlying writer. 221 * 222 * @param s The <code>String</code> to be printed 223 * @throws java.io.IOException If an error occured while writing 224 */ 225 226 abstract public void print(String s) throws IOException; 227 228 /** 229 * Print an object. The string produced by the <code>{@link 230 * java.lang.String#valueOf(Object)}</code> method is written to the 231 * JspWriter's buffer or, if no buffer is used, directly to the 232 * underlying writer. 233 * 234 * @param obj The <code>Object</code> to be printed 235 * @see java.lang.Object#toString() 236 * @throws java.io.IOException If an error occured while writing 237 */ 238 239 abstract public void print(Object obj) throws IOException; 240 241 /** 242 * Terminate the current line by writing the line separator string. The 243 * line separator string is defined by the system property 244 * <code>line.separator</code>, and is not necessarily a single newline 245 * character (<code>'\n'</code>). 246 * @throws java.io.IOException If an error occured while writing 247 */ 248 249 abstract public void println() throws IOException; 250 251 /** 252 * Print a boolean value and then terminate the line. This method behaves 253 * as though it invokes <code>{@link #print(boolean)}</code> and then 254 * <code>{@link #println()}</code>. 255 * 256 * @param x the boolean to write 257 * @throws java.io.IOException If an error occured while writing 258 */ 259 260 abstract public void println(boolean x) throws IOException; 261 262 /** 263 * Print a character and then terminate the line. This method behaves as 264 * though it invokes <code>{@link #print(char)}</code> and then <code>{@link 265 * #println()}</code>. 266 * 267 * @param x the char to write 268 * @throws java.io.IOException If an error occured while writing 269 */ 270 271 abstract public void println(char x) throws IOException; 272 273 /** 274 * Print an integer and then terminate the line. This method behaves as 275 * though it invokes <code>{@link #print(int)}</code> and then <code>{@link 276 * #println()}</code>. 277 * 278 * @param x the int to write 279 * @throws java.io.IOException If an error occured while writing 280 */ 281 282 abstract public void println(int x) throws IOException; 283 284 /** 285 * Print a long integer and then terminate the line. This method behaves 286 * as though it invokes <code>{@link #print(long)}</code> and then 287 * <code>{@link #println()}</code>. 288 * 289 * @param x the long to write 290 * @throws java.io.IOException If an error occured while writing 291 */ 292 293 abstract public void println(long x) throws IOException; 294 295 /** 296 * Print a floating-point number and then terminate the line. This method 297 * behaves as though it invokes <code>{@link #print(float)}</code> and then 298 * <code>{@link #println()}</code>. 299 * 300 * @param x the float to write 301 * @throws java.io.IOException If an error occured while writing 302 */ 303 304 abstract public void println(float x) throws IOException; 305 306 /** 307 * Print a double-precision floating-point number and then terminate the 308 * line. This method behaves as though it invokes <code>{@link 309 * #print(double)}</code> and then <code>{@link #println()}</code>. 310 * 311 * @param x the double to write 312 * @throws java.io.IOException If an error occured while writing 313 */ 314 315 abstract public void println(double x) throws IOException; 316 317 /** 318 * Print an array of characters and then terminate the line. This method 319 * behaves as though it invokes <code>print(char[])</code> and then 320 * <code>println()</code>. 321 * 322 * @param x the char[] to write 323 * @throws java.io.IOException If an error occured while writing 324 */ 325 326 abstract public void println(char x[]) throws IOException; 327 328 /** 329 * Print a String and then terminate the line. This method behaves as 330 * though it invokes <code>{@link #print(String)}</code> and then 331 * <code>{@link #println()}</code>. 332 * 333 * @param x the String to write 334 * @throws java.io.IOException If an error occured while writing 335 */ 336 337 abstract public void println(String x) throws IOException; 338 339 /** 340 * Print an Object and then terminate the line. This method behaves as 341 * though it invokes <code>{@link #print(Object)}</code> and then 342 * <code>{@link #println()}</code>. 343 * 344 * @param x the Object to write 345 * @throws java.io.IOException If an error occured while writing 346 */ 347 348 abstract public void println(Object x) throws IOException; 349 350 351 /** 352 * Clear the contents of the buffer. If the buffer has been already 353 * been flushed then the clear operation shall throw an IOException 354 * to signal the fact that some data has already been irrevocably 355 * written to the client response stream. 356 * 357 * @throws IOException If an I/O error occurs 358 */ 359 360 abstract public void clear() throws IOException; 361 362 /** 363 * Clears the current contents of the buffer. Unlike clear(), this 364 * method will not throw an IOException if the buffer has already been 365 * flushed. It merely clears the current content of the buffer and 366 * returns. 367 * 368 * @throws IOException If an I/O error occurs 369 */ 370 371 abstract public void clearBuffer() throws IOException; 372 373 /** 374 * Flush the stream. If the stream has saved any characters from the 375 * various write() methods in a buffer, write them immediately to their 376 * intended destination. Then, if that destination is another character or 377 * byte stream, flush it. Thus one flush() invocation will flush all the 378 * buffers in a chain of Writers and OutputStreams. 379 * <p> 380 * The method may be invoked indirectly if the buffer size is exceeded. 381 * <p> 382 * Once a stream has been closed, 383 * further write() or flush() invocations will cause an IOException to be 384 * thrown. 385 * 386 * @exception IOException If an I/O error occurs 387 */ 388 389 abstract public void flush() throws IOException; 390 391 /** 392 * Close the stream, flushing it first. 393 * <p> 394 * This method needs not be invoked explicitly for the initial JspWriter 395 * as the code generated by the JSP container will automatically 396 * include a call to close(). 397 * <p> 398 * Closing a previously-closed stream, unlike flush(), has no effect. 399 * 400 * @exception IOException If an I/O error occurs 401 */ 402 403 abstract public void close() throws IOException; 404 405 /** 406 * This method returns the size of the buffer used by the JspWriter. 407 * 408 * @return the size of the buffer in bytes, or 0 is unbuffered. 409 */ 410 411 public int getBufferSize() { return bufferSize; } 412 413 /** 414 * This method returns the number of unused bytes in the buffer. 415 * 416 * @return the number of bytes unused in the buffer 417 */ 418 419 abstract public int getRemaining(); 420 421 /** 422 * This method indicates whether the JspWriter is autoFlushing. 423 * 424 * @return if this JspWriter is auto flushing or throwing IOExceptions 425 * on buffer overflow conditions 426 */ 427 428 public boolean isAutoFlush() { return autoFlush; } 429 430 /* 431 * fields 432 */ 433 434 /** 435 * The size of the buffer used by the JspWriter. 436 */ 437 protected int bufferSize; 438 439 /** 440 * Whether the JspWriter is autoflushing. 441 */ 442 protected boolean autoFlush; 443 }