native_dpr.html

JNI(java本地接口)之delphi版

  WriteLn(str);

    <font color="#003399"><i>// Create a JString and return it</i></font>
  Result := JVM.NewStringUTF(PAnsiChar(Str));

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


<font color="#003399"><i>(****************************************************************************
 *  Java declaration:
 *     native public void printObjectArray(Object[] array);
 *
 *  Given an array of Objects, each element is printed using the
 *  'toString' method of the Object.
 *
 *  Class:     Native
 *  Method:    printObjectArray
 *  Signature: ([Ljava/lang/Object;Z)V
 *)</i></font>
<b>procedure</b> Java_Native_printObjectArray(PEnv: PJNIEnv; Obj: JObject; ObjArray: JObjectArray; Print: JBoolean); <b>stdcall</b>;
<b>var</b>
  Cls: JClass;
  Mid: JMethodID;
  Ob: JObject;
  Element: JObject;
  S: JString;
  Str: <b>string</b>;
  Len, I: Integer;
  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 length of the array</i></font>
  len := JVM.GetArrayLength(ObjArray);

    <font color="#003399"><i>// Make sure we have at least one object in the array</i></font>
  <b>if</b> Len &lt; 1 <b>then</b>
    exit;

    <font color="#003399"><i>// Get an element of the array so we can get the right 'toString' method</i></font>
  Ob := JVM.GetObjectArrayElement(ObjArray, 0);

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

  <b>if</b> Cls = <b>nil</b> <b>then</b>
  <b>begin</b>
    WriteLn(<font color="#9933CC">'Can'</font><font color="#9933CC">'t GetObjectClass'</font>);
    exit;
  <b>end</b>;

    <font color="#003399"><i>// Get method ID for the 'toString' method of this object's class</i></font>
  Mid := JVM.GetMethodID(Cls, <font color="#9933CC">'toString'</font>, <font color="#9933CC">'()Ljava/lang/String;'</font>);

    <font color="#003399"><i>// We will check this also</i></font>
  <b>if</b> Mid = <b>nil</b> <b>then</b>
  <b>begin</b>
    WriteLn(<font color="#9933CC">'Can'</font><font color="#9933CC">'t GetMethodID for toString'</font>);
    exit;
  <b>end</b>;

    <font color="#003399"><i>// Loop the the array of objects and print out each one using</i></font>
    <font color="#003399"><i>// the 'toString' method of its ancestor class Object</i></font>
  <b>for</b> I := 0 <b>to</b> Len - 1 <b>do</b>
  <b>begin</b>

      <font color="#003399"><i>// Get the next element from the array</i></font>
    Element := JVM.GetObjectArrayElement(ObjArray, i);

      <font color="#003399"><i>// Call the 'toString' method, which returns a String representation</i></font>
      <font color="#003399"><i>// of Rectangle object.</i></font>
    S := JVM.CallObjectMethodA(Element, Mid, <b>nil</b>);

      <font color="#003399"><i>// The actual printing can be turned on/off. This was useful during</i></font>
      <font color="#003399"><i>// debugging when passing thousands of elements into the procedure.</i></font>
    <b>if</b> Print &lt;&gt; False <b>then</b>
    <b>begin</b>
      Str := JVM.JStringToString(S);
      WriteLn(Str);
    <b>end</b>;
  <b>end</b>;

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


<font color="#003399"><i>(****************************************************************************
 *  Java declaration:
 *     native public jobjectarray returnRectArray(int size);
 *
 *  This function creates an array of 'size' Rectangles and returns them
 *  to the Java caller. First, the array is created, then each element
 *  is assigned a Rectangle object.
 *
 *  Class:     Native
 *  Method:    returnRectArray
 *  Signature: (I)[Ljava/awt/Rectangle;
 *)</i></font>
<b>function</b> Java_Native_returnRectArray(PEnv: PJNIEnv; Obj: JObject; Size: JInt): JObjectArray; <b>stdcall</b>;
<b>var</b>
  Cls: JClass;
  Mid: JMethodID;
  Element: JObject;
  JOArray: JObjectArray;
  I: Integer;
  Args: <b>array</b>[0..3] <b>of</b> JValue;
  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>// Find the Rectangle class</i></font>
  Cls := JVM.FindClass(<font color="#9933CC">'java/awt/Rectangle'</font>);
  <b>if</b> Cls = <b>nil</b> <b>then</b>
  <b>begin</b>
    WriteLn(<font color="#9933CC">'Can'</font><font color="#9933CC">'t FindClass(java/awt/Rectangle'</font>);
    Result := <b>nil</b>;
    exit;
  <b>end</b>;

    <font color="#003399"><i>// Get its constructor (the one that takes 4 integers)</i></font>
  Mid := JVM.GetMethodID(Cls, <font color="#9933CC">'&lt;init&gt;'</font>, <font color="#9933CC">'(IIII)V'</font>);
  <b>if</b> Mid = <b>nil</b> <b>then</b>
  <b>begin</b>
    WriteLn(<font color="#9933CC">'Can'</font><font color="#9933CC">'t get MethodID for Rectangle constructor'</font>);
    Result := <b>nil</b>;
    exit;
  <b>end</b>;

    <font color="#003399"><i>// Allocate the array of Rectangles</i></font>
  JOArray := JVM.NewObjectArray(Size, Cls, <b>nil</b>);

    <font color="#003399"><i>// Now initialize each one to a Rectangle</i></font>
  <b>for</b> I := 0 <b>to</b> Size - 1 <b>do</b>
  <b>begin</b>

      <font color="#003399"><i>// Create a new Rectangle object</i></font>
    Args[0].i := 0;
    Args[1].i := 0;
    Args[2].i := 5 * I;
    Args[3].i := 10 * I;
    Element := JVM.NewObjectA(Cls, Mid, @args);

      <font color="#003399"><i>// Assign the Rectangle to an element of the array</i></font>
    JVM.SetObjectArrayElement(JOArray, I, Element);

  <b>end</b>;

    <font color="#003399"><i>// Return the array back to the Java client</i></font>
  Result := JOArray;

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


<font color="#003399"><i>(****************************************************************************
 *  Java declaration:
 *     native public void handleException();
 *
 *  Causes an exception in the JVM, but detects it and supresses it
 *
 *  Class:     Native
 *  Method:    handleException
 *  Signature: ()V
 *)</i></font>
<b>procedure</b> Java_Native_handleException(PEnv: PJNIEnv; Obj: JObject); <b>stdcall</b>;
<b>var</b>
  Cls: JClass;
  AException: JThrowable;
  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 to which this object belongs</i></font>
  Cls := JVM.GetObjectClass(Obj);

    <font color="#003399"><i>// Attempt to get the ID of the 'nonexistent' member, which, not by</i></font>
    <font color="#003399"><i>// chance, doesn't exist!</i></font>
  JVM.GetFieldID(Cls, <font color="#9933CC">'nonexistent'</font>, <font color="#9933CC">'Ljava/lang/String;'</font>);

    <font color="#003399"><i>// Check for exception</i></font>
  AException := JVM.ExceptionOccurred;

    <font color="#003399"><i>// exception is non-zero if an exception occurred</i></font>
  <b>if</b> (AException &lt;&gt; <b>nil</b>) <b>then</b>
  <b>begin</b>

    <font color="#003399"><i>//WriteLn('Exception occurred in Native code and was handled. This was the exception:');</i></font>
    Writeln(Format(<font color="#9933CC">'Exception handled in Main.cpp: %d'</font>, [DWORD(AException)]));

      <font color="#003399"><i>// This call will print out a description of the exception</i></font>
    <font color="#003399"><i>//JVM.ExceptionDescribe(PEnv);</i></font>

      <font color="#003399"><i>// Clear the exception so the JVM doesn't react to it after we handled it</i></font>
    JVM.ExceptionClear;

  <b>end</b>;

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


<font color="#003399"><i>(****************************************************************************
 *  Java declaration:
 *     native public void causeException();
 *
 *  Causes an exception in the JVM, but fails to catch it. Thus, it is
 *  propagated back to the JVM.
 *
 *  Class:     Native
 *  Method:    causeException
 *  Signature: ()V
 *)</i></font>
<b>procedure</b> Java_Native_causeException(PEnv: PJNIEnv; Obj: JObject); <b>stdcall</b>;
<b>var</b>
  Cls: JClass;
  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 to which this object belongs</i></font>
  Cls := JVM.GetObjectClass(Obj);

    <font color="#003399"><i>// Attempt to get the ID of the 'nonexistent' member, which, not by</i></font>
    <font color="#003399"><i>// chance, doesn't exist!</i></font>
  JVM.GetFieldID(Cls, <font color="#9933CC">'nonexistent'</font>, <font color="#9933CC">'Ljava/lang/String;'</font>);

    <font color="#003399"><i>// An exception has occurred, but it has not been suppressed.</i></font>
    <font color="#003399"><i>// The JVM will detect it and catch it.</i></font>
    <font color="#003399"><i>// Because we don't call this: JVM.ExceptionClear(PEnv),</i></font>
    <font color="#003399"><i>// the JVM will react.</i></font>

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


<font color="#003399"><i>(****************************************************************************
 *  Java declaration:
 *     native public void pass2DByteArray(byte[][] array);
 *
 *  Pass a 2-D array of Bytes from Java. This method will retrieve each
 *  element from the arrays, print it, then multiply it by 10 and store
 *  the new Value back into the array. This is to show access/updating
 *  of 2-D arrays within native code. The process would be similar for
 *  3-D arrays.
 *
 *  Class:     Native
 *  Method:    pass2DByteArray
 *  Signature: ([[B)V
 *)</i></font>
<b>procedure</b> Java_Native_pass2DByteArray(PEnv: PJNIEnv; Obj: JObject; Array2D: JObjectArray); <b>stdcall</b>;
<b>var</b>
  NumArrays: UINT;
  Len: UINT;
  I, J: Integer;
  JBArray: JByteArray;
  Elements: PJByte;
  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 length of the array (number of arrays)</i></font>
  NumArrays := JVM.GetArrayLength(Array2D);

  WriteLn(<font color="#9933CC">'In native method printing 2-D byte array.'</font>);
  WriteLn(<font color="#9933CC">'Each element is then multiplied by 10 and updated.'</font>);

    <font color="#003399"><i>// Loop over each array</i></font>
  <b>for</b> I := 0 <b>to</b> NumArrays - 1 <b>do</b>
  <b>begin</b>

      <font color="#003399"><i>// Get the object at the i'th position (it's an array of Bytes)</i></font>
    JBArray := JVM.GetObjectArrayElement(Array2D, i);

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

        <font color="#003399"><i>// Get the elements from the Byte array</i></font>
    Elements := JVM.GetByteArrayElements(JBArray, IsCopy);