[转帖]使用JAYDEBEAPI同时连接两个不同数据库（ORACLE+MYSQL）的问题

jaydebeapi 同时连接两种数据库

在使用jaydebeapi只连接一种数据库时，是没问题的，但是如果需要同时连接两种数据库，比如同时连接oracle和mysql

例如以下测试代码：

1.  
   import jaydebeapi ##使用jdbc驱动连接数据库
2.  
   import pandas as pd
3.  
    
4.  
   dirver='oracle.jdbc.driver.OracleDriver'
5.  
   jarFile='D:\\WORK\\PYScript\\BiDataMonitor\\jdbc\\64\\ojdbc14.jar'
6.  
   addr_='xxx.xxx.xxx.xxx'+':'+'1521'+'/'+'xxx'
7.  
   url='jdbc:oracle:thin:@'+addr_
8.  
   print('url',url)
9.  
   DBUser='用户名'
10.  
    DBPwd='密码'
11.  
    conn=jaydebeapi.connect(dirver,[url,DBUser,DBPwd],jarFile) ##使用jdbc驱动连接数据库
12.  
    sql_str="select 'oracle' from dual"
13.  
    df=pd.read_sql_query(sql_str,conn)
14.  
    print(df)
15.  
    conn.close()
16.  
     
17.  
     
18.  
    dirver='com.mysql.jdbc.Driver'
19.  
    jarFile='D:\\WORK\\PYScript\\BiDataMonitor\\jdbc\\64\\mysql-connector-java-5.1.30.jar'
20.  
    addr_='xxx.xxx.xxx.xxx'+':'+'3306'+'/'+'xxx'
21.  
    url='jdbc:mysql://'+addr_
22.  
    print('url',url)
23.  
    DBUserMySql='用户名'
24.  
    DBPwdMySql='密码'
25.  
    conn2=jaydebeapi.connect(dirver,[url,DBUserMySql,DBPwdMySql],jarFile)
26.  
    sql_str="select 'mysql' from dual"
27.  
    df=pd.read_sql_query(sql_str,conn2)
28.  
    print(df)
29.  
    conn2.close()

在连接第二种数据库时，就会报错误：

1.  
   Py4JJavaError: An error occurred while calling z:java.sql.DriverManager.getConnection.
2.  
   : java.sql.SQLException: No suitable driver found for jdbc:mysql://10.1.164.5:3306/vvm
3.  
   at java.sql.DriverManager.getConnection(Unknown Source)
4.  
   at java.sql.DriverManager.getConnection(Unknown Source)
5.  
   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
6.  
   at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
7.  
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
8.  
   at java.lang.reflect.Method.invoke(Unknown Source)
9.  
   at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:244)
10.  
    at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:357)
11.  
    at py4j.Gateway.invoke(Gateway.java:282)
12.  
    at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132)
13.  
    at py4j.commands.CallCommand.execute(CallCommand.java:79)
14.  
    at py4j.GatewayConnection.run(GatewayConnection.java:214)
15.  
    at java.lang.Thread.run(Unknown Source)

错误信息中显示，找不到渠道，而实际上并不是驱动或者jar包的问题。

要分析和解决这个问题，还需要从jaydebeapi的源码中分析，打开jaydebeapi源码（下载地址：https://pypi.python.org/pypi/JayDeBeApi3），从报错信息中我们可以得到，是在...jaydebeapi\__init__.py", line 68

jaydebeapi.connect方法源码如下：

1.  
   # DB-API 2.0 Module Interface connect constructor
2.  
   def connect(jclassname, driver_args, jars=None, libs=None):
3.  
   """Open a connection to a database using a JDBC driver and return
4.  
   a Connection instance.
5.  
    
6.  
   jclassname: Full qualified Java class name of the JDBC driver.
7.  
   driver_args: Argument or sequence of arguments to be passed to the
8.  
   Java DriverManager.getConnection method. Usually the
9.  
   database URL. See
10.  
    http://docs.oracle.com/javase/6/docs/api/java/sql/DriverManager.html
11.  
    for more details
12.  
    jars: Jar filename or sequence of filenames for the JDBC driver
13.  
    libs: Dll/so filenames or sequence of dlls/sos used as shared
14.  
    library by the JDBC driver
15.  
    """
16.  
     
17.  
    if _gateway_is_running():
18.  
    gateway = java_gateway.JavaGateway()
19.  
    else:
20.  
    driver_args = [driver_args] if isinstance(driver_args, str) else driver_args
21.  
     
22.  
    if jars:
23.  
    classpath = os.pathsep.join(jars) if isinstance(jars, list) else jars
24.  
    else:
25.  
    classpath = None
26.  
     
27.  
    if libs:
28.  
    javaopts = libs if isinstance(libs, list) else [libs]
29.  
    else:
30.  
    javaopts = []
31.  
     
32.  
    gateway = java_gateway.JavaGateway.launch_gateway(
33.  
    port=25333, classpath=classpath, javaopts=javaopts, die_on_exit=True)
34.  
     
35.  
    java_gateway.java_import(gateway.jvm, 'java.sql.DriverManager')
36.  
    gateway.jvm.Class.forName(jclassname)
37.  
     
38.  
    connection = gateway.jvm.DriverManager.getConnection(*driver_args)
39.  
    if _converters is None:
40.  
    types_map = {}
41.  
    for type in gateway.jvm.Class.forName("java.sql.Types").getFields():
42.  
    types_map[type.getName()] = type.getInt(None)
43.  
    _init_converters(types_map)
44.  
     
45.  
    return Connection(connection, _converters)

报错信息中提示的68行也就是：

connection = gateway.jvm.DriverManager.getConnection(*driver_args)

其实，我不需要跟深层次是剖析，只需要分析下jaydebeapi.connect方法即可，该方法大概是逻辑是：

1.  
   判断 java_gateway是否running
2.  
               |----------是---|-----否-----|
3.  
               | |
4.  
   获取gateway实例     1、初始化参数
5.  
       2、创建gateway实例

问题就出在这里，第一次连接oracle时，通过右边分支先初始化参数，然后创建了gateway实例，但是第二次调用jaydebeapi.connect方法连mysql时，由于_gateway_is_running()返回真，所以走左边分支，直接获取了上一次连接oracle时创建gateway实例，其中最重要的两个个参数jclassname和classpath，也就是“oracle.jdbc.driver.OracleDriver”和"ojdbc14.jar"

1.  
   gateway = java_gateway.JavaGateway.launch_gateway(
2.  
   port=25333, classpath=classpath, javaopts=javaopts, die_on_exit=True)
3.  
    
4.  
   java_gateway.java_import(gateway.jvm, 'java.sql.DriverManager')
5.  
   gateway.jvm.Class.forName(jclassname)

而第二次连mysql时，用的是mysql的连接，所以当然就是报No suitable driver found for jdbc错误。

明白了报错的原因，下面就来需求解决方法

解决的方法应该有多种，我这里采取了最简单，最暴力的方法，就是在判断_gateway_is_running()时，将其关闭，然后重新重建新的gateway实例，这样虽然简单，但是如果频繁连接数据库时，就会因为不能重用上一次实例而消耗额外的资源。

通过帮助函数可知，gateway实例有一个shutdown方法

修改后的connect方法如下：

1.  
   # DB-API 2.0 Module Interface connect constructor
2.  
   def connect(jclassname, driver_args, jars=None, libs=None):
3.  
   """Open a connection to a database using a JDBC driver and return
4.  
   a Connection instance.
5.  
    
6.  
   jclassname: Full qualified Java class name of the JDBC driver.
7.  
   driver_args: Argument or sequence of arguments to be passed to the
8.  
   Java DriverManager.getConnection method. Usually the
9.  
   database URL. See
10.  
    http://docs.oracle.com/javase/6/docs/api/java/sql/DriverManager.html
11.  
    for more details
12.  
    jars: Jar filename or sequence of filenames for the JDBC driver
13.  
    libs: Dll/so filenames or sequence of dlls/sos used as shared
14.  
    library by the JDBC driver
15.  
    """
16.  
     
17.  
    if _gateway_is_running():
18.  
    gateway = java_gateway.JavaGateway()
19.  
    gateway.shutdown()
20.  
    else:
21.  
    pass
22.  
    driver_args = [driver_args] if isinstance(driver_args, str) else driver_args
23.  
     
24.  
    if jars:
25.  
    classpath = os.pathsep.join(jars) if isinstance(jars, list) else jars
26.  
    else:
27.  
    classpath = None
28.  
     
29.  
    if libs:
30.  
    javaopts = libs if isinstance(libs, list) else [libs]
31.  
    else:
32.  
    javaopts = []
33.  
     
34.  
    gateway = java_gateway.JavaGateway.launch_gateway(
35.  
    port=25333, classpath=classpath, javaopts=javaopts, die_on_exit=True)
36.  
     
37.  
    java_gateway.java_import(gateway.jvm, 'java.sql.DriverManager')
38.  
    gateway.jvm.Class.forName(jclassname)
39.  
     
40.  
    connection = gateway.jvm.DriverManager.getConnection(*driver_args)
41.  
    if _converters is None:
42.  
    types_map = {}
43.  
    for type in gateway.jvm.Class.forName("java.sql.Types").getFields():
44.  
    types_map[type.getName()] = type.getInt(None)
45.  
    _init_converters(types_map)
46.  
     
47.  
    return Connection(connection, _converters)

然后卸载jaydebeapi，用修改后的源码重新安装一次即可，源码安装方法，可以查看之前的一篇博客：

https://blog.csdn.net/cakecc2008/article/details/79073181