0049.htm

JspServlet教程专栏 对javaservlet讲述的非常详细

160 log = new PrintWriter(new FileWriter(logFile, true), true);
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161 }
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162 catch (IOException e) {
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163 System.err.println(&quot;无法打开日志文件: &quot; + logFile);
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164 log = new PrintWriter(System.err);
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165 }
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166 loadDrivers(dbProps);
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167 createPools(dbProps);
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168 }
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169
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170 /**
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171 * 装载和注册所有JDBC驱动程序
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172 *
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173 * @param props 属性
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174 */
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175 private void loadDrivers(Properties props) {
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176 String driverClasses = props.getProperty(&quot;drivers&quot;);
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177 StringTokenizer st = new StringTokenizer(driverClasses);
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178 while (st.hasMoreElements()) {
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179 String driverClassName = st.nextToken().trim();
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180 try {
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181 Driver driver = (Driver)
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182 Class.forName(driverClassName).newInstance();
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183 DriverManager.registerDriver(driver);
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184 drivers.addElement(driver);
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185 log(&quot;成功注册JDBC驱动程序&quot; + driverClassName);
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186 }
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187 catch (Exception e) {
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188 log(&quot;无法注册JDBC驱动程序: &quot; +
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189 driverClassName + &quot;, 错误: &quot; + e);
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190 }
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191 }
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192 }
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193
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194 /**
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195 * 将文本信息写入日志文件
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196 */
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197 private void log(String msg) {
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198 log.println(new Date() + &quot;: &quot; + msg);
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199 }
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200
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201 /**
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202 * 将文本信息与异常写入日志文件
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203 */
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204 private void log(Throwable e, String msg) {
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205 log.println(new Date() + &quot;: &quot; + msg);
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206 e.printStackTrace(log);
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207 }
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208
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209 /**
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210 * 此内部类定义了一个连接池.它能够根据要求创建新连接,直到预定的最
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211 * 大连接数为止.在返回连接给客户程序之前,它能够验证连接的有效性.
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212 */
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213 class DBConnectionPool {
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214 private int checkedOut;
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215 private Vector freeConnections = new Vector();
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216 private int maxConn;
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217 private String name;
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218 private String password;
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219 private String URL;
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220 private String user;
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221
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222 /**
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223 * 创建新的连接池
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224 *
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225 * @param name 连接池名字
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226 * @param URL 数据库的JDBC URL
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227 * @param user 数据库帐号,或 null
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228 * @param password 密码,或 null
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229 * @param maxConn 此连接池允许建立的最大连接数
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230 */
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231 public DBConnectionPool(String name, String URL, String user, String password,
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232 int maxConn) {
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233 this.name = name;
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234 this.URL = URL;
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235 this.user = user;
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236 this.password = password;
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237 this.maxConn = maxConn;
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238 }
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239
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240 /**
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241 * 将不再使用的连接返回给连接池
<br>
242 *
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243 * @param con 客户程序释放的连接
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244 */
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245 public synchronized void freeConnection(Connection con) {
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246 // 将指定连接加入到向量末尾
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247 freeConnections.addElement(con);
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248 checkedOut--;
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249 notifyAll();
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250 }
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251
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252 /**
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253 * 从连接池获得一个可用连接.如没有空闲的连接且当前连接数小于最大连接
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254 * 数限制,则创建新连接.如原来登记为可用的连接不再有效,则从向量删除之,
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255 * 然后递归调用自己以尝试新的可用连接.
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256 */
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257 public synchronized Connection getConnection() {
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258 Connection con = null;
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259 if (freeConnections.size() &gt; 0) {
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260 // 获取向量中第一个可用连接
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261 con = (Connection) freeConnections.firstElement();
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262 freeConnections.removeElementAt(0);
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263 try {
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264 if (con.isClosed()) {
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265 log(&quot;从连接池&quot; + name+&quot;删除一个无效连接&quot;);
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266 // 递归调用自己,尝试再次获取可用连接
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267 con = getConnection();
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268 }
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269 }
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270 catch (SQLException e) {
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271 log(&quot;从连接池&quot; + name+&quot;删除一个无效连接&quot;);
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272 // 递归调用自己,尝试再次获取可用连接
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273 con = getConnection();
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274 }
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275 }
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276 else if (maxConn == 0 || checkedOut &lt; maxConn) {
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277 con = newConnection();
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278 }
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279 if (con != null) {
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280 checkedOut++;
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281 }
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282 return con;
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283 }
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284
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285 /**
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286 * 从连接池获取可用连接.可以指定客户程序能够等待的最长时间
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287 * 参见前一个getConnection()方法.
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288 *
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289 * @param timeout 以毫秒计的等待时间限制
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290 */
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291 public synchronized Connection getConnection(long timeout) {
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292 long startTime = new Date().getTime();
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293 Connection con;
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294 while ((con = getConnection()) == null) {
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295 try {
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296 wait(timeout);
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297 }
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298 catch (InterruptedException e) {}
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299 if ((new Date().getTime() - startTime) &gt;= timeout) {
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300 // wait()返回的原因是超时
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301 return null;
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302 }
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303 }
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304 return con;
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305 }
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306
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307 /**
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308 * 关闭所有连接
<br>
309 */
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310 public synchronized void release() {
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311 Enumeration allConnections = freeConnections.elements();
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312 while (allConnections.hasMoreElements()) {
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313 Connection con = (Connection) allConnections.nextElement();
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314 try {
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315 con.close();
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316 log(&quot;关闭连接池&quot; + name+&quot;中的一个连接&quot;);
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317 }
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318 catch (SQLException e) {
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319 log(e, &quot;无法关闭连接池&quot; + name+&quot;中的连接&quot;);
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320 }
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321 }
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322 freeConnections.removeAllElements();
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323 }
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324
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325 /**
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326 * 创建新的连接
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327 */
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328 private Connection newConnection() {
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329 Connection con = null;
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330 try {
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331 if (user == null) {
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332 con = DriverManager.getConnection(URL);
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333 }
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334 else {
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335 con = DriverManager.getConnection(URL, user, password);
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336 }
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337 log(&quot;连接池&quot; + name+&quot;创建一个新的连接&quot;);
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338 }
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339 catch (SQLException e) {
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340 log(e, &quot;无法创建下列URL的连接: &quot; + URL);
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341 return null;
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342 }
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343 return con;
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344 }
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345 }
<br>
346 }
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