什么是validationQuery？

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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
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"));    }}1
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创建“db.validation.properties”文件，并放置在classpath目录下

#hsqldborg.hsqldb.jdbcDriver=select 1 from INFORMATION_SCHEMA.SYSTEM_USERS#Oracleoracle.jdbc.driver.OracleDriver=select 1 from dual#DB2com.ibm.db2.jcc.DB2Driver=select 1 from sysibm.sysdummy1#mysqlcom.mysql.jdbc.Driver=select 1org.gjt.mm.mysql.Driver=select 1#microsoft sqlcom.microsoft.sqlserver.jdbc.SQLServerDriver=select 1#postgresqlorg.postgresql.Driver=select version();#ingrescom.ingres.jdbc.IngresDriver=select 1#derbyorg.apache.derby.jdbc.ClientDriver=values 1#H2org.h2.Driver=select 1

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