C In JSTL: key points and skills of set labels

C: The set tag has two different settings: var and target. Var "version" is used to set the scope attribute, and target "version" is used to set the bean attribute or Map value. Both versions have two forms: ry and ry. There is only another way to put values.★Var "version" <c: set var = "userLevel" scope = "session" value = "Cowboy"/> <c: set var = "fido" value = "$ {person. dog} "/> <c: set var =" user "scope =" session "> Sheriff, bariff, Cowgirl </c: set> If" value "is null, the attribute specified by "var" will be deleted! If the property specified by "var" does not exist, an attribute is created, but a new attribute is created only when "value" is not null.★Target "version" <c: set target = "$ {petMap}" property = "dogName" value = "Clover" scope = "session"/> <c: set target = "$ {person}" property = "name" >$ {foo. name} </c: set> If "target" is a Map, "property" specifies a key of the Map. If "target" is a bean, "property" specifies a member field of the bean. If the target expression is null, the container throws an exception. If the target expression is not a Map or bean, the container throws an exception. If the "target" expression is a bean, but the bean does not have a member field that matches the "property", the container will throw an exception.★The key points for using the c: set tag cannot have the "var" and "target" attributes at the same time. "Scope" is optional. If this attribute is not used, the page scope is used by default. Specifically, when this attribute is not used, the container searches for the page scope, request scope, session scope, and application scope in sequence. If the scope attribute specified by "var" is not found, the container creates a new attribute in the page scope. If the object specified by "target" cannot be found, the container throws an exception.