What does the servlet load-on-startup value signify

Question

I am getting a bit confused here  In our application we are having a few servlets defined  Here is the excerpt from the web xml for one of the servlets    lt servlet gt       lt servlet-name gt AxisServlet lt  servlet-name gt       lt display-name gt Apache-Axis Servlet lt  display-name gt       lt servlet-class gt com foo framework axis2 http FrameworkServlet lt  servlet-class gt       lt load-on-startup gt 0 lt  load-on-startup gt   lt  servlet gt     As per my understanding the value for the  lt load-on-startup gt  has to be a positive integer in order for it to get loaded automatically  I looked up on google but the responses I came across only added to my confusion

User · Answer

yes it can have same value    the reason for giving numbers to load-on-startup is to define a sequence for server to load all the servlet  servlet with 0 load-on-startup value will load first and servlet with value 1 will load after that    if two servlets will have the same value for load-on-startup than it will be loaded how they are declared in the web xml from top to bottom  the servlet which comes first in the web xml will be loaded first and the other will be loaded after that

User · Answer

The servlet container loads the servlet during startup or when the first request is made  The loading of the servlet depends on the attribute  load-on-startup  in  web xml  file  If the attribute  has a positive integer 0 to 128  then the servlet is load with the loading of the container otherwise it loads when the first request comes for service   When the servlet is loaded once it gets request then it is called  Lazy loading

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If the value is  lt 0  the serlet is instantiated when the request comes  else   0 the container will load in the increasing order of the values  if 2 or more servlets have the same value  then the order of the servlets declared in the web xml

User · Answer

It is simple as you don t even expect   If the value is positive it loaded when the container starts  If the value is not positive than the servelet is loaded when the request is made

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Short Answer  value    0 means that the servlet is loaded when the web-app is deployed or when the server starts  value  lt  0   servlet is loaded whenever the container feels like   Long answer  from the spec       The load-on-startup element indicates that this   servlet should be loaded  instantiated and have   its init   called  on the startup of the web   application  The optional contents of these   element must be an integer indicating the order in   which the servlet should be loaded  If the value   is a negative integer  or the element is not   present  the container is free to load the servlet   whenever it chooses  If the value is a positive   128   integer or 0  the container must load and   initialize the servlet as the application is   deployed  The container must guarantee that   servlets marked with lower integers are loaded   before servlets marked with higher integers  The   container may choose the order of loading of   servlets with the same load-on-start-up value

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If  value is same for two servlet than they will be loaded in an order on which they are declared inside web xml file  if  is 0 or negative integer than Servlet will be loaded when Container feels to load them   guarantees loading  initialization and call to init   method of servlet by web container  If there is no  element for any servlet than they will be loaded when web container decides to load them

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--    Absence of load-on-start-up  tag First of all when ever servlet is deployed in the server  It is the responsibility of the server to creates the servlet object     Eg  Suppose Servlet is deployed in the server   Servlet Object is not available in server  client sends the request to the servlet for the first time then server creates the servlet object with help of default constructor  and immediately calls init     From that when ever client sends the request only service method will get executed as object is already available  If load-on-start-up tag is used in deployment descriptor     At the time of deployment itself the server creates the servlet object for the servlets based on the positive value provided in between the tags  The Creation of objects for the servlet classes will follow from 0-128  0 number servlet will be created first and followed by other numbers   If we provide same value for two servlets in web xml then creation of objects will be done based on the position of classes in web xml also varies from server to server   If we provide negative value in between the load on start up tag then server wont create the servlet object    Other Scenarios where server creates the object for servlet   If we dont use load on start up tag in web xml  then project is deployed when ever client sends the request for the first time server creates the object and server is responsible for calling its life cycle methods  Then if a  class is been modified in the server tomcat   again client sends the request for modified servlet but in case of tomcat new object will not created and server make use of existing object unless restart of server takes place  But in class of web-logic when ever  class file is modified in the server with out restarting the server if it receives a request then server calls the destroy method on existing servlet and creates a new servlet object and calls init   for its initilization

User · Answer

As stated on other answer and this load-on-startup article zero is acceptable and in the absent of any other servlet this will take priority on loading and loaded during deployment  Best use of load-on statup is to load servlets which takes longer time to initialize well before first request come like servlets which creates connection pool or make network call or hold bulky resource  this will significantly reduce response time for first few request

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Servlet Life Cycle     The lifecycle of a servlet is controlled by the container in which the servlet has been deployed  When a request is mapped to a servlet  the container performs the following steps          If an instance of the servlet does not exist  the web container       a  Loads the servlet class      b  Creates an instance of the servlet class      c  Initializes the servlet instance by calling the init method  initialization is covered in Creating and Initializing a Servlet    The container invokes the service method  passing request and response objects  Service methods are discussed in Writing Service Methods       A 0 value on load-on-startup means that point 1 is executed when a request comes to that servlet  Other values means that point 1 is executed at container startup

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It indicates that the servlet won t be started until a request tries to access it   If load-on-startup is greater than or equal to zero then when the container starts it will start that servlet in ascending order of the load on startup value you put there  ie 0  1 then 2 then 5 then 10 and so on

User · Answer

Resin 3 0 documents this behavior      load-on-startup can specify an  optional  integer value  If the value is 0 or greater    it indicates an order for servlets to be loaded  servlets with higher numbers get   loaded after servlets with lower numbers    The JSP 3 1 spec  JSR 340  says this on page 14-160      The element load-on-startup indicates that this servlet should be loaded  instantiated   and have its   init   called  on the startup of the Web application  The element content of this   element must be an integer indicating the order in which the servlet should be   loaded  If the value is a negative integer  or the element is not present  the   container is free to load the servlet whenever it chooses  If the value is a positive   integer or 0  the container must load and initialize the servlet as the application is   deployed  The container must guarantee that servlets marked with lower integers   are loaded before servlets marked with higher integers  The container may choose   the order of loading of servlets with the same load-on-startup value     You probably want to check not only the JSR  but also the documentation for your web container   There may be differences

[jakarta-ee] What does the servlet <load-on-startup> value signify

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