native_dpr.html

JNI(java本地接口)之delphi版

      <font color="#003399"><i>// Print each element, then multiply the Value by 10</i></font>
      <font color="#003399"><i>// and put it back into the array. (This is to prove that</i></font>
      <font color="#003399"><i>// the array elements have changed when this function returns</i></font>
      <font color="#003399"><i>// to Java code.</i></font>
    <b>for</b> J := 0 <b>to</b> Len - 1 <b>do</b>
    <b>begin</b>
      WriteLn(Format(<font color="#9933CC">'%d,%d = %d'</font>, [I, J, Elements^]));

        <font color="#003399"><i>// Update the element (just multiply it by 10)</i></font>
      Elements^ := Elements^ * 10;
      Inc(Elements);
    <b>end</b>;
  <b>end</b>;

  JVM.Free;
<b>end</b>;


<font color="#003399"><i>(****************************************************************************
 *  This is a sample algorithm that I got from Microsoft's documentation.
 *  I used it as the initial test case. I may have modified it slightly.
 *
 *  The interesting point in this example is that the function is declared
 *  as 'static' in the Java code. The only difference at the native level
 *  is that the second parameter is a 'JClass' instead of a 'JObject'.
 *  Most functions are non-static, and so require a handle to the object
 *  rather than the class.
 *
 *  Java declaration:
 *    native public static int countPrimes(byte[] array);
 *
 *  Class:     Native
 *  Method:    countPrimes
 *  Signature: ([B)I
 *)</i></font>
<b>function</b> Java_Native_countPrimes(PEnv: PJNIEnv; Cls: JClass; ByteArray: JByteArray): JInt; <b>stdcall</b>;
<b>var</b>
  Count, Len: ULONG;
  I, J: ULONG;
  Body: PJByte;
  IsCopy: JBoolean;
  Ptr: PChar;
  JVM: TJNIEnv;
<b>begin</b>
    <font color="#003399"><i>// Create an instance of the Java environment</i></font>
  JVM := TJNIEnv.Create(PEnv);

    <font color="#003399"><i>// Get the length of the array</i></font>
  Len := JVM.GetArrayLength(ByteArray);

    <font color="#003399"><i>// Get a pointer to the elements of the array. Only primitive elements</i></font>
    <font color="#003399"><i>// can be accessed this way.</i></font>
  Body := JVM.GetByteArrayElements(ByteArray, IsCopy);

    <font color="#003399"><i>// Since body is not a Delphi array (Body is of type PJByte), we need to use</i></font>
    <font color="#003399"><i>// a PChar (interchangeable with arrays) to access the java array using an</i></font>
    <font color="#003399"><i>// index (e.g.  Body[0] is illegal, but Ptr[0] is legal)</i></font>
  Ptr := PChar(Body);

    <font color="#003399"><i>// Initialize all elements</i></font>
  <b>for</b> I := 0 <b>to</b> Len - 1 <b>do</b>
    Ptr[i] := #1;

  Count := 0;

    <font color="#003399"><i>// Set each element at a non-prime index to 0</i></font>
  <b>for</b> I := 2 <b>to</b> Len - 1 <b>do</b>
  <b>begin</b>
    <b>if</b> Ptr[I] &lt;&gt; #0 <b>then</b>
    <b>begin</b>
      J := I + I;
      <b>while</b> J &lt; len <b>do</b>
      <b>begin</b>
        Ptr[J] := #0;
        Inc(J, I);
      <b>end</b>;
      Inc(Count);
    <b>end</b>;
  <b>end</b>;

    <font color="#003399"><i>// The number of primes between 1 and array.length</i></font>
  Result := Count;

<b>end</b>;


<font color="#003399"><i>(****************************************************************************
 *  Java declaration:
 *     native public void VoidVoid();
 *
 *  This function takes no arguments and returns nothing. Just used to
 *  demonstrate the most simplistic function call. Also used to time
 *  function call overhead in the simplest case.
 *
 *  Class:     Native
 *  Method:    VoidVoid
 *  Signature: ()V
 *)</i></font>
<b>procedure</b> Java_Native_VoidVoid(PEnv: PJNIEnv; Obj: JObject); <b>stdcall</b>;
<font color="#003399"><i>//var</i></font>
  <font color="#003399"><i>//JVM: TJNIEnv;</i></font>
<b>begin</b>
    <font color="#003399"><i>// These two lines of code take about 1 ms to execute on a PIII 450 MHz</i></font>
  <font color="#003399"><i>//JVM := TJNIEnv.Create(PEnv);</i></font>
  <font color="#003399"><i>//JVM.Free;</i></font>
<b>end</b>;


<font color="#003399"><i>(****************************************************************************
 *  A private native function that calls back into Java. Calls a void
 *  function just for timings.
 *
 *  Class:     Native
 *  Method:    callbackVoid
 *  Signature: (I)V
 *)</i></font>
<b>procedure</b> Java_Native_callbackVoid(PEnv: PJNIEnv; Obj: JObject; Count: JInt); <b>stdcall</b>;
<b>var</b>
  Cls: JClass;
  Mid: JMethodID;
  I: JInt;
  JVM: TJNIEnv;
<b>begin</b>
    <font color="#003399"><i>// Create an instance of the Java environment</i></font>
  JVM := TJNIEnv.Create(PEnv);

    <font color="#003399"><i>// Get the class that this object belongs to</i></font>
  Cls := JVM.GetObjectClass(Obj);

    <font color="#003399"><i>// Get the method ID for 'void voidFunc()'</i></font>
  Mid := JVM.GetMethodID(Cls, <font color="#9933CC">'voidFunc'</font>, <font color="#9933CC">'()V'</font>);

    <font color="#003399"><i>// If we can't find the ID, just return. This kind of check should be in all</i></font>
    <font color="#003399"><i>// functions in this code, but it isn't (for brevity)</i></font>
  <b>if</b> (Mid = <b>nil</b>) <b>then</b>
    exit;

    <font color="#003399"><i>// Perform the callbacks</i></font>
  <b>for</b> I := 0 <b>to</b> Count - 1 <b>do</b>
    JVM.CallVoidMethodA(Obj, Mid, <b>nil</b>);

<b>end</b>;


<font color="#003399"><i>(****************************************************************************
 *  Java declaration:
 *     native public void printVersion();
 *
 *  Prints the version of the JDK being used.
 *
 *  Class:     Native
 *  Method:    printVersion
 *  Signature: ()V
 *)</i></font>
<b>procedure</b> Java_Native_printVersion(PEnv: PJNIEnv; Obj: JObject); <b>stdcall</b>;
<b>var</b>
  JVM: TJNIEnv;
  Major, Minor: JInt;
<b>begin</b>
  JVM := TJNIEnv.Create(PEnv);
  Major := JVM.MajorVersion;
  Minor := JVM.MinorVersion;
  WriteLn(Format(<font color="#9933CC">'The Java version is %d.%d'</font>, [Major, Minor]));
<b>end</b>;


<font color="#003399"><i>(****************************************************************************
 *  Java declaration:
 *     native public void testAllTypesD();
 *
 *  Tests all data types. Shows how floats passed in open arrays to JNI
 *  methods are not handled correctly.
 *
 * Class:     Native
 * Method:    testAllTypesD
 * Signature: (ZBCIJFD)V
 *)</i></font>
<b>procedure</b> Java_Native_testAllTypesD(PEnv: PJNIEnv; Obj: JObject; Bool: JBoolean; B: JByte; C: JChar; I: JInt; L: JLong; F: jfloat; D: jdouble); <b>stdcall</b>;
<b>var</b>
  Cls: JClass;
  Mid: JMethodID;
  JVM: TJNIEnv;
<b>begin</b>
    <font color="#003399"><i>// Create an instance of the Java environment</i></font>
  JVM := TJNIEnv.Create(PEnv);

    <font color="#003399"><i>// Get the class associated with this object</i></font>
  Cls := JVM.GetObjectClass(Obj);

    <font color="#003399"><i>// The ID for the testAllTypes method</i></font>
  Mid := JVM.GetMethodID(Cls, <font color="#9933CC">'testAllTypes'</font>, <font color="#9933CC">'(ZBCIJFD)V'</font>);

    <font color="#003399"><i>// Call it</i></font>
  JVM.CallVoidMethod(Obj, Mid, [Bool, B, C, I, L, F, D]);

<b>end</b>;


<font color="#003399"><i>(****************************************************************************
 *  Java declaration:
 *     native public void multiplyIntegers(int op1, int op2);
 *
 *  Multiplies 2 integers and returns the result.
 *
 *  Class:     Native
 *  Method:    multiplyIntegers
 *  Signature: (II)I
*)</i></font>
<b>function</b> Java_Native_multiplyIntegers(PEnv: PJNIEnv; Obj: JObject; Op1: JInt; Op2: JInt): jint; <b>stdcall</b>;
<b>begin</b>
  Result := Op1 * Op2;
<b>end</b>;


<font color="#003399"><i>(****************************************************************************
 *  Java declaration:
 *     native public void initializeByteArrayOnce(byte[] byteArray, byte Value);
 *
 *  Initializes each element of an array with the value 'Value'. This function
 *  is an overloaded version of the one used to test performance.
 *
 *  Class:     Native
 *  Method:    initializeByteArrayOnce
 *  Signature: ([BB)V
 *)</i></font>
<b>procedure</b> Java_Native_initializeByteArray(PEnv: PJNIEnv; Obj: JObject; ByteArray: JByteArray; Value: JByte); <b>stdcall</b>; overload;
<b>var</b>
  Elements: PJByte;
  PE: PJByte;
  Len: DWORD;
  I: Longint;
  IsCopy: JBoolean;
  JVM: TJNIEnv;
<b>begin</b>
    <font color="#003399"><i>// Create an instance of the Java environment</i></font>
  JVM := TJNIEnv.Create(PEnv);

    <font color="#003399"><i>// Get elements of the array.</i></font>
  elements := JVM.GetByteArrayElements(ByteArray, IsCopy);

    <font color="#003399"><i>// Get length of the array.</i></font>
  Len := JVM.GetArrayLength(ByteArray);

    <font color="#003399"><i>// Assign 'Value' to each element.</i></font>
  PE := Elements;
  <b>for</b> I := 0 <b>to</b> Len - 1 <b>do</b>
  <b>begin</b>
    PE^ := Value;
    Inc(PE);
  <b>end</b>;

    <font color="#003399"><i>// Release the elements of the array.</i></font>
  JVM.ReleaseByteArrayElements(ByteArray, Elements, 0);

  JVM.Free;
<b>end</b>;


<font color="#003399"><i>(*******************************************************************************
  Make these routines available to Java.
*******************************************************************************)</i></font>
<b>exports</b>
  Java_Native_initializeByteArray(PEnv: PJNIEnv; Obj: JObject; ByteArray: JByteArray; Count: JInt; Value: JByte)name <font color="#9933CC">'Java_Native_initializeByteArray'</font>,
  Java_Native_initializeByteArray(PEnv: PJNIEnv; Obj: JObject; ByteArray: JByteArray; Value: JByte)name <font color="#9933CC">'Java_Native_initializeByteArrayOnce'</font>,
  Java_Native_callbackVoid,
  Java_Native_causeException,
  Java_Native_countPrimes,
  Java_Native_displayHelloWorld,
  Java_Native_handleException,
  Java_Native_multiplyIntegers,
  Java_Native_pass2DByteArray,
  Java_Native_printLine,
  Java_Native_printObjectArray,
  Java_Native_printVersion,
  Java_Native_printWXYZ,
  Java_Native_returnRectArray,
  Java_Native_testAllTypesD,
  Java_Native_toStringWithPrint,
  Java_Native_VoidVoid;

<b>begin</b>
<b>end</b>.
</code></pre>
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