Java tutorial
package bboss.org.apache.velocity.runtime.resource.loader; /* * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, * software distributed under the License is distributed on an * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * KIND, either express or implied. See the License for the * specific language governing permissions and limitations * under the License. */ import java.io.BufferedInputStream; import java.io.InputStream; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Timestamp; import javax.naming.InitialContext; import javax.naming.NamingException; import javax.sql.DataSource; import org.apache.commons.collections.ExtendedProperties; import bboss.org.apache.velocity.exception.ResourceNotFoundException; import bboss.org.apache.velocity.exception.VelocityException; import bboss.org.apache.velocity.runtime.resource.Resource; import bboss.org.apache.velocity.util.ExceptionUtils; import bboss.org.apache.velocity.util.StringUtils; /** * <P>This is a simple template file loader that loads templates * from a DataSource instead of plain files. * * <P>It can be configured with a datasource name, a table name, * id column (name), content column (the template body) and a * datetime column (for last modification info). * <br> * <br> * Example configuration snippet for velocity.properties: * <br> * <br> * resource.loader = file, ds <br> * <br> * ds.resource.loader.public.name = DataSource <br> * ds.resource.loader.description = Velocity DataSource Resource Loader <br> * ds.resource.loader.class = bboss.org.apache.velocity.runtime.resource.loader.DataSourceResourceLoader <br> * ds.resource.loader.resource.datasource = java:comp/env/jdbc/Velocity <br> * ds.resource.loader.resource.table = tb_velocity_template <br> * ds.resource.loader.resource.keycolumn = id_template <br> * ds.resource.loader.resource.templatecolumn = template_definition <br> * ds.resource.loader.resource.timestampcolumn = template_timestamp <br> * ds.resource.loader.cache = false <br> * ds.resource.loader.modificationCheckInterval = 60 <br> * <br> * <P>Optionally, the developer can instantiate the DataSourceResourceLoader and set the DataSource via code in * a manner similar to the following: * <BR> * <BR> * DataSourceResourceLoader ds = new DataSourceResourceLoader();<BR> * ds.setDataSource(DATASOURCE);<BR> * Velocity.setProperty("ds.resource.loader.instance",ds);<BR> * <P> The property <code>ds.resource.loader.class</code> should be left out, otherwise all the other * properties in velocity.properties would remain the same. * <BR> * <BR> * * Example WEB-INF/web.xml: <br> * <br> * <resource-ref> <br> * <description>Velocity template DataSource</description> <br> * <res-ref-name>jdbc/Velocity</res-ref-name> <br> * <res-type>javax.sql.DataSource</res-type> <br> * <res-auth>Container</res-auth> <br> * </resource-ref> <br> * <br> * <br> * and Tomcat 4 server.xml file: <br> * [...] <br> * <Context path="/exampleVelocity" docBase="exampleVelocity" debug="0"> <br> * [...] <br> * <ResourceParams name="jdbc/Velocity"> <br> * <parameter> <br> * <name>driverClassName</name> <br> * <value>org.hsql.jdbcDriver</value> <br> * </parameter> <br> * <parameter> <br> * <name>driverName</name> <br> * <value>jdbc:HypersonicSQL:database</value> <br> * </parameter> <br> * <parameter> <br> * <name>user</name> <br> * <value>database_username</value> <br> * </parameter> <br> * <parameter> <br> * <name>password</name> <br> * <value>database_password</value> <br> * </parameter> <br> * </ResourceParams> <br> * [...] <br> * </Context> <br> * [...] <br> * <br> * Example sql script:<br> * CREATE TABLE tb_velocity_template ( <br> * id_template varchar (40) NOT NULL , <br> * template_definition text (16) NOT NULL , <br> * template_timestamp datetime NOT NULL <br> * ) <br> * * @author <a href="mailto:wglass@forio.com">Will Glass-Husain</a> * @author <a href="mailto:matt@raibledesigns.com">Matt Raible</a> * @author <a href="mailto:david.kinnvall@alertir.com">David Kinnvall</a> * @author <a href="mailto:paulo.gaspar@krankikom.de">Paulo Gaspar</a> * @author <a href="mailto:lachiewicz@plusnet.pl">Sylwester Lachiewicz</a> * @author <a href="mailto:henning@apache.org">Henning P. Schmiedehausen</a> * @version $Id: DataSourceResourceLoader.java 991660 2010-09-01 19:13:46Z nbubna $ * @since 1.5 */ public class DataSourceResourceLoader extends ResourceLoader { private String dataSourceName; private String tableName; private String keyColumn; private String templateColumn; private String timestampColumn; private InitialContext ctx; private DataSource dataSource; /** * @see bboss.org.apache.velocity.runtime.resource.loader.ResourceLoader#init(org.apache.commons.collections.ExtendedProperties) */ public void init(ExtendedProperties configuration) { dataSourceName = StringUtils.nullTrim(configuration.getString("resource.datasource")); tableName = StringUtils.nullTrim(configuration.getString("resource.table")); keyColumn = StringUtils.nullTrim(configuration.getString("resource.keycolumn")); templateColumn = StringUtils.nullTrim(configuration.getString("resource.templatecolumn")); timestampColumn = StringUtils.nullTrim(configuration.getString("resource.timestampcolumn")); if (dataSource != null) { if (log.isDebugEnabled()) { log.debug("DataSourceResourceLoader: using dataSource instance with table \"" + tableName + "\""); log.debug("DataSourceResourceLoader: using columns \"" + keyColumn + "\", \"" + templateColumn + "\" and \"" + timestampColumn + "\""); } log.trace("DataSourceResourceLoader initialized."); } else if (dataSourceName != null) { if (log.isDebugEnabled()) { log.debug("DataSourceResourceLoader: using \"" + dataSourceName + "\" datasource with table \"" + tableName + "\""); log.debug("DataSourceResourceLoader: using columns \"" + keyColumn + "\", \"" + templateColumn + "\" and \"" + timestampColumn + "\""); } log.trace("DataSourceResourceLoader initialized."); } else { String msg = "DataSourceResourceLoader not properly initialized. No DataSource was identified."; log.error(msg); throw new RuntimeException(msg); } } /** * Set the DataSource used by this resource loader. Call this as an alternative to * specifying the data source name via properties. * @param dataSource The data source for this ResourceLoader. */ public void setDataSource(final DataSource dataSource) { this.dataSource = dataSource; } /** * @see bboss.org.apache.velocity.runtime.resource.loader.ResourceLoader#isSourceModified(bboss.org.apache.velocity.runtime.resource.Resource) */ public boolean isSourceModified(final Resource resource) { return (resource.getLastModified() != readLastModified(resource, "checking timestamp")); } /** * @see bboss.org.apache.velocity.runtime.resource.loader.ResourceLoader#getLastModified(bboss.org.apache.velocity.runtime.resource.Resource) */ public long getLastModified(final Resource resource) { return readLastModified(resource, "getting timestamp"); } /** * Get an InputStream so that the Runtime can build a * template with it. * * @param name name of template * @return InputStream containing template * @throws ResourceNotFoundException */ public synchronized InputStream getResourceStream(final String name) throws ResourceNotFoundException { if (org.apache.commons.lang.StringUtils.isEmpty(name)) { throw new ResourceNotFoundException("DataSourceResourceLoader: Template name was empty or null"); } Connection conn = null; ResultSet rs = null; PreparedStatement ps = null; try { conn = openDbConnection(); ps = getStatement(conn, templateColumn, name); rs = ps.executeQuery(); if (rs.next()) { InputStream stream = rs.getBinaryStream(templateColumn); if (stream == null) { throw new ResourceNotFoundException( "DataSourceResourceLoader: " + "template column for '" + name + "' is null"); } return new BufferedInputStream(stream); } else { throw new ResourceNotFoundException( "DataSourceResourceLoader: " + "could not find resource '" + name + "'"); } } catch (SQLException sqle) { String msg = "DataSourceResourceLoader: database problem while getting resource '" + name + "': "; log.error(msg, sqle); throw new ResourceNotFoundException(msg); } catch (NamingException ne) { String msg = "DataSourceResourceLoader: database problem while getting resource '" + name + "': "; log.error(msg, ne); throw new ResourceNotFoundException(msg); } finally { closeResultSet(rs); closeStatement(ps); closeDbConnection(conn); } } /** * Fetches the last modification time of the resource * * @param resource Resource object we are finding timestamp of * @param operation string for logging, indicating caller's intention * * @return timestamp as long */ private long readLastModified(final Resource resource, final String operation) { long timeStamp = 0; /* get the template name from the resource */ String name = resource.getName(); if (name == null || name.length() == 0) { String msg = "DataSourceResourceLoader: Template name was empty or null"; log.error(msg); throw new NullPointerException(msg); } else { Connection conn = null; ResultSet rs = null; PreparedStatement ps = null; try { conn = openDbConnection(); ps = getStatement(conn, timestampColumn, name); rs = ps.executeQuery(); if (rs.next()) { Timestamp ts = rs.getTimestamp(timestampColumn); timeStamp = ts != null ? ts.getTime() : 0; } else { String msg = "DataSourceResourceLoader: could not find resource " + name + " while " + operation; log.error(msg); throw new ResourceNotFoundException(msg); } } catch (SQLException sqle) { String msg = "DataSourceResourceLoader: database problem while " + operation + " of '" + name + "': "; log.error(msg, sqle); throw ExceptionUtils.createRuntimeException(msg, sqle); } catch (NamingException ne) { String msg = "DataSourceResourceLoader: database problem while " + operation + " of '" + name + "': "; log.error(msg, ne); throw ExceptionUtils.createRuntimeException(msg, ne); } finally { closeResultSet(rs); closeStatement(ps); closeDbConnection(conn); } } return timeStamp; } /** * Gets connection to the datasource specified through the configuration * parameters. * * @return connection */ private Connection openDbConnection() throws NamingException, SQLException { if (dataSource != null) { return dataSource.getConnection(); } if (ctx == null) { ctx = new InitialContext(); } dataSource = (DataSource) ctx.lookup(dataSourceName); return dataSource.getConnection(); } /** * Closes connection to the datasource */ private void closeDbConnection(final Connection conn) { if (conn != null) { try { conn.close(); } catch (RuntimeException re) { throw re; } catch (Exception e) { String msg = "DataSourceResourceLoader: problem when closing connection"; log.error(msg, e); throw new VelocityException(msg, e); } } } /** * Closes the result set. */ private void closeResultSet(final ResultSet rs) { if (rs != null) { try { rs.close(); } catch (RuntimeException re) { throw re; } catch (Exception e) { String msg = "DataSourceResourceLoader: problem when closing result set"; log.error(msg, e); throw new VelocityException(msg, e); } } } /** * Closes the PreparedStatement. */ private void closeStatement(PreparedStatement ps) { if (ps != null) { try { ps.close(); } catch (RuntimeException re) { throw re; } catch (Exception e) { String msg = "DataSourceResourceLoader: problem when closing PreparedStatement "; log.error(msg, e); throw new VelocityException(msg, e); } } } /** * Creates the following PreparedStatement query : * <br> * SELECT <i>columnNames</i> FROM <i>tableName</i> WHERE <i>keyColumn</i> * = '<i>templateName</i>' * <br> * where <i>keyColumn</i> is a class member set in init() * * @param conn connection to datasource * @param columnNames columns to fetch from datasource * @param templateName name of template to fetch * @return PreparedStatement */ private PreparedStatement getStatement(final Connection conn, final String columnNames, final String templateName) throws SQLException { PreparedStatement ps = conn .prepareStatement("SELECT " + columnNames + " FROM " + tableName + " WHERE " + keyColumn + " = ?"); ps.setString(1, templateName); return ps; } }