Jstl operations on Map sets

1. Iteration

When the expression value in the items attribute of foreach is Java. util. MAP, the type of the variable named IN VaR is

Java. util. Map. Entry. If Var = entry, use the expression $ {entry. Key} to get the key name.

Use the expression $ {entry. Value} to obtain the value of each entry. This is because java. util. Map. entry objects include getkey and getvalue

The Expression Language complies with the naming conventions of JavaBean.

Example:

<C: foreach items = "$ {map}" Var = "entry">

<C: Out value = "$ {entry. Key}"/>

<C: Out value = "$ {entry. Value}"/>

</C: foreach>

2. Evaluate the value based on the key variable

If you know the key in advance, it is easy to get the value object according to $ {map. Key Value}. What if the key is a variable?

One problem is how to use el to get an object for a given key variable. here we need to use [] in the El expression to solve this problem,

The solution is as follows:

<C: Out value = "$ {map [Key]}"/>

<! -- The map here is the java. util. map object, and the key is a key in the map -->