Method example of how to get parameter name in Java 8

Preface

In versions before Java 8, after the code is compiled into a class file, the types of method parameters are fixed, but the parameter names are lost. This is in stark contrast to dynamic languages ​​that rely heavily on parameter names. Compared. Now, Java 8 begins to retain parameter names in class files, which brings great convenience to reflection.

Example:

public class GetRuntimeParameterName {
 
 public void createUser(String name, int age, int version) {
  //
 }
 
 public static void main(String[] args) throws Exception {
  for (Method m : GetRuntimeParameterName.class.getMethods()) {
   System.out.println("----------------------------------------");
   System.out.println(" method: " + m.getName());
   System.out.println(" return: " + m.getReturnType().getName());
   for (Parameter p : m.getParameters()) {
    System.out.println("parameter: " + p.getType().getName() + ", " + p.getName());
   }
  }
 }
}

Method.getParameters is a new method for 1.8, which can obtain parameter information, including parameter names.

The createUser parameters output by the above code are as follows:

method: createUser
 return: void
parameter: java.lang.String, name
parameter: int, age
parameter: int, version

The parameter names are compiled into the class file, replacing the meaningless arg0, arg1...# in the earlier version.

##For many frameworks that rely on parameter names, the code can be further simplified:

@Path("/groups/:groupid/:userid")
public User getUser(String groupid, String userid) {
 ...
}

When there is no parameter name, annotations must be added:

@Path("/groups/:groupid/:userid")
public User getUser(@Param("groupid") String groupid, @Param("userid") String userid) {
 ...
}

Unfortunately, the option to retain parameter names is turned on by the compile switch javac -parameters, and is turned off by default.

In Eclipse, you can open it through the Compiler option:

Note: This function must compile the code into version 1.8 class.

Summary

The above is the entire content of this article. I hope the content of this article can bring some help to everyone's study or work. If you have any questions, you can leave a message to communicate.

For more related articles on how to get parameter names in Java 8, please pay attention to the PHP Chinese website!