Android Development Practice: Jni function Signature Generator

"Function signing" is common in Android NDK development, and because Java supports overloading, a method can only be determined by the function name alone. Thus, JNI provides a set of signature rules that uniquely identify a Java-side defined native method with a string.

The signature string for each of the Java data types is as follows (from the introduction of the Oracle website JNI):

650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M01/56/FD/wKiom1SOxRfjmgaBAAHVKEL-bG0476.jpg "title=" Oracle _jni.png "alt=" Wkiom1soxrfjmgabaahvkel-bg0476.jpg "/>

The principle is not complex, each basic type corresponds to a single character signature, and the class corresponds to the "L" + class of the full path + ";", the array type corresponds to the "[" + element type of signature, the signature of the function is: (each parameter type signature) + return type signature.

Figuring out the fundamentals, we can try customizing a Java tool class to generate a signature string for the Java native function, with the following code:

/* *  copyright notice   *  copyright  (C)  2014,  ticktick <[email protected]> *  http://ticktick.blog.51cto.com/ *     *   @license  under the apache license, version 2.0   * *   @file     SignatureGen.java *   @brief     Implement a java class for jni signature generate *    *   @version  1.0      *   @author    ticktick *   @date     2014/12/15   *  */package  com.ticktick.library;import java.util.HashMap;public class SignatureGen {     public static final HashMap<String,String> Primitives =  New hashmap<string,&nBsp String> ();    static {         Primitives.put (Void.class.getName (), "V");         primitives.put ( Boolean.class.getName (), "Z");         primitives.put (Byte.class.getName (), "B"),         primitives.put (Character.class.getName (), "C");         primitives.put (Short.class.getName (), "S");         primitives.put (Integer.class.getName (), "I");         primitives.put (Long.class.getName (), "J");         primitives.put ( Float.class.getName (), "F");         primitives.put (Double.class.getName (), "D");    }             Public static string&nbSp;getsignature ( Class ret, Class...params )  {         stringbuilder builder = new stringbuilder ();         builder.append ("(");         for ( Class  param : params )  {             Builder.append (Getsignature (param));        }         builder.append (")");         builder.append ( Getsignature (ret));         return builder.tostring ();     }    protected static string getsignature ( Class  param )  {        stringbuilder builder = new  stringbuilder ();         string name =  "";         if ( param.isarray ()  )  {             name = param.getcomponenttype (). GetName ();             builder.append ("[");        }         else {             name = param.getname ();        }             if ( primitives.containskey (name)  )  {    builder.append (Primitives.get (name));         }        else {              Builder.append ("L" +name.replace (".", "/") + ";");         }           Return builder.tostring ();     }}

the Signaturegen class provides a function getsignature that supports arguments to obtain a signature string for a Java function, the first parameter is a class object of the function return value type, and the argument is a class object of each function parameter type .

For example, print out a signature string for a different type of function, as shown below.

LOG.D ("Signature", "void func ()--" + signaturegen.getsignature (void.class)); LOG.D ("Signature", "Boolean func ()--" + signaturegen.getsignature (boolean.class)); LOG.D ("Signature", "int func (Boolean a)--" + signaturegen.getsignature (integer.class,boolean.class)); LOG.D ("Signature", "int func (Boolean a,string B)--" + Signaturegen.getsignature (Integer.class,boolean.class, String.class)); LOG.D ("Signature", "int func (byte[] c)--" + signaturegen.getsignature (integer.class,byte[].class)); LOG.D ("Signature", "long func (int n,string str,int arr)--" + Signaturegen.getsignature (Long.class,integer.class, String.class,integer[].class));

The output screenshot is as follows:

650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M01/56/FB/wKioL1SOyGLycSFiAAFsjPzuhjU727.jpg "title=" Test_ Out.png "alt=" Wkiol1soyglycsfiaafsjpzuhju727.jpg "/>

About the JNI function signature Generator introduced here, the principle is not complex so I did not carry out too much analysis, I hope this tool can be useful in future projects, have any questions welcome message or letter [email protected] exchange.

This article is from the "Shadow Three People" blog, please be sure to keep this source http://ticktick.blog.51cto.com/823160/1590209

Android Development Practice: Jni function Signature Generator