servlet 인 int 되는 시점에서 공유 변수 설정을 하기 위해서
System.setProperty 를 이용해서 값을 저장후 서블릿 단에서  getProperty 를 통해서 호출 한다..
게시판 구현시 dbcp접속 servlet이 int되는 시점에서
dbType을 저장 하는데 활용 했음 .

setProperty

public static String setProperty(String key,
                                 String value)

Sets the system property indicated by the specified key.

First, if a security manager exists, its SecurityManager.checkPermission method is called with a PropertyPermission(key, "write") permission. This may result in a SecurityException being thrown. If no exception is thrown, the specified property is set to the given value.

Parameters:

key - the name of the system property.

value - the value of the system property.

Returns:

the previous value of the system property, or null if it did not have one.

Throws:

SecurityException - if a security manager exists and its checkPermission method doesn't allow setting of the specified property.

NullPointerException - if key or value is null.

IllegalArgumentException - if key is empty.

Since:

1.2

See Also:

getProperty(java.lang.String), getProperty(java.lang.String), getProperty(java.lang.String, java.lang.String), PropertyPermission, SecurityManager.checkPermission(java.security.Permission)





getProperty

public static String getProperty(String key,
                                 String def)

Gets the system property indicated by the specified key.

First, if there is a security manager, its checkPropertyAccess method is called with the key as its argument.

If there is no current set of system properties, a set of system properties is first created and initialized in the same manner as for the getProperties method.

Parameters:

key - the name of the system property.

def - a default value.

Returns:

the string value of the system property, or the default value if there is no property with that key.

Throws:

SecurityException - if a security manager exists and its checkPropertyAccess method doesn't allow access to the specified system property.

NullPointerException - if key is null.

IllegalArgumentException - if key is empty.

See Also:

setProperty(java.lang.String, java.lang.String), SecurityManager.checkPropertyAccess(java.lang.String), getProperties()

public static String getProperty(String key)

Gets the system property indicated by the specified key.

First, if there is a security manager, its checkPropertyAccess method is called with the key as its argument. This may result in a SecurityException.

If there is no current set of system properties, a set of system properties is first created and initialized in the same manner as for the getProperties method.

Parameters:

key - the name of the system property.

Returns:

the string value of the system property, or null if there is no property with that key.

Throws:

SecurityException - if a security manager exists and its checkPropertyAccess method doesn't allow access to the specified system property.

NullPointerException - if key is null.

IllegalArgumentException - if key is empty.

See Also:

setProperty(java.lang.String, java.lang.String), SecurityException, SecurityManager.checkPropertyAccess(java.lang.String), getProperties()