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DBCP针对不同数据库的validationQuery
当你使用DBCP连接池时，你可以通过设置testOnBorrow和testOnReturn属性测试这个连接是否可用。不幸的是你还需要设置validationQuery才能起作用。那么问题来了如何设置validationQuery这个值呢？
什么是validationQuery？
validationQuery是用来验证数据库连接的查询语句，这个查询语句必须是至少返回一条数据的SELECT语句。每种数据库都有各自的验证语句，下表中收集了几种常见数据库的validationQuery。
DataBasevalidationQueryhsqldbselect 1 from INFORMATION_SCHEMA.SYSTEM_USERSOracleselect 1 from dualDB2select 1 from sysibm.sysdummy1MySqlselect 1Microsoft SqlServerselect1postgresqlselect version()ingresselect 1derbyvalues 1H2select 1
根据JDBC驱动获取validationQuery
如果你想支持多种数据库，你可以根据JDBC驱动来获取validationQuery，这里有个简单的类，根据JDBC驱动名称来获取validationQuery
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
public class ValidationQuery {
public String getValidationQuery(String driver) {
Properties properties = loadProperties();
return properties.getProperty(driver, "");
}
private Properties loadProperties() {
String propertyFilename = "db.validation.properties";
try {
Properties props = new Properties();
InputStream resourceAsStream = this.getClass().
getClassLoader().getResourceAsStream(propertyFilename);
props.load(resourceAsStream);
resourceAsStream.close();
return props;
} catch (IOException e) {
throw new RuntimeException("Cannot load properties file '" + propertyFilename + "'.", e);
}
}
//Example: Get validationQuery for hsqldb
public static void main(String[] args) {
System.out.println(new ValidationQuery().getValidationQuery("org.hsqldb.jdbcDriver"));
}
}
创建“db.validation.properties”文件，并放置在classpath目录下
#hsqldb
org.hsqldb.jdbcDriver=select 1 from INFORMATION_SCHEMA.SYSTEM_USERS
#Oracle
oracle.jdbc.driver.OracleDriver=select 1 from dual
#DB2
com.ibm.db2.jcc.DB2Driver=select 1 from sysibm.sysdummy1
#mysql
com.mysql.jdbc.Driver=select 1
org.gjt.mm.mysql.Driver=select 1
#microsoft sql
com.microsoft.sqlserver.jdbc.SQLServerDriver=select 1
#postgresql
org.postgresql.Driver=select version();
#ingres
com.ingres.jdbc.IngresDriver=select 1
#derby
org.apache.derby.jdbc.ClientDriver=values 1
#H2
org.h2.Driver=select 1