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2、Pass a string to/from Java to/from CTag(s): JNI

天下 — Fri, 06 Dec 2019 02:53:00 GMT

Pass a string to/from Java to/from CTag(s): JNI

To Java from C (as seen from the previous How-to) :

#include "JavaHowTo.h"

JNIEXPORT jstring JNICALL Java_JavaHowTo_sayHello
  (JNIEnv *env, jobject obj) {
    return  env->NewStringUTF("Hello world");
}
From Java to C : Suppose we have a Java Class
public class MyClass {
  public String sayHello(){
     return  "Hello world From Java";
  }
}

then from C, we want to call the Java sayHello() method which returns a String :

JNIEXPORT void JNICALL Java_JavaHowTo_sayHello(JNIEnv *env, jobject obj)
{
    const char *str;

    jclass myclass_class =(jclass) env->NewGlobalRef
         (env->FindClass ("MyClass"));

    // we need the MyClass constructor
    jmethodID constructorID = env->GetMethodID
         (myclass_class, "", "()V");

    // and the sayHello() method
    jmethodID methodID = env->GetMethodID
         (myclass_class, "sayHello", "()Ljava/lang/String;");

    // instanciate a MyClass object
    jobject myclass_object =  env->NewObject
         (myclass_class, constructorID);

    // call the sayHello() method
    jstring s = (jstring)  env->CallObjectMethod
         (myclass_object, methodID);

    // convert the Java String to use it in C
    str = env->GetStringUTFChars(s, 0);
    printf("%s" , str);
    env->ReleaseStringUTFChars(s, str);
}

The Java JNI wrapper would be

class JavaHowTo {
  public native void sayHello();
  static {
    System.loadLibrary("javahowto");
  }
}

And finally, to use it

public class JNIJavaHowTo {
  public static void main(String[] args) {
    JavaHowTo jht = new JavaHowTo();
    jht.sayHello();
    }
}

天下 2019-12-06 10:53 发表评论

1、Use native code through JNI (HelloWorld)

天下 — Fri, 06 Dec 2019 02:50:00 GMT

https://www.rgagnon.com/topics/java-jni.html

Use native code through JNI (HelloWorld)

Use native code through JNITag(s): JNI

With MSVC6, create a new Win32 DLL project (simple) and call it javahowto.

In the same directory create a java source called JavaHowTo.java

class JavaHowTo {
  public native String sayHello();
  static {
    System.loadLibrary("javahowto");
  }
}

Compile the Java program and use javah utility to generate the JavaHowTo.h header file.

javah -jni JavaHowTo

In MSVC6, add the JavaHowTo.h in your project header files

In the Tools - Options menu, set the include directories to include the Java JNI headers files. They are located in [jdk dir]\include and [jdk dir]\include\win32 directories

In the javahowto.cpp source, add

#include "JavaHowTo.h"

JNIEXPORT jstring JNICALL Java_JavaHowTo_sayHello
(JNIEnv *env, jobject obj) {
return env->NewStringUTF("Hello world");
}

Select the Release configuration and build the project.

Copy the javahowto.dll in the same directory as the java program.

Create this new java program

public class JNIJavaHowTo {
  public static void main(String[] args) {
    JavaHowTo jht = new JavaHowTo();
    System.out.println(jht.sayHello());
    }
}

Compile and execute.

天下 2019-12-06 10:50 发表评论

天下 — Tue, 12 Feb 2019 03:44:00 GMT

spring 官方下蝲地址�Q�Spring Framework 3.2.x&Spring Framework 4.0.x�Q?br />2017�q?2�?4�?15:53:59

SPRING官方�|�站改版后，��都是通过 Maven和Gradle下蝲�Q�对不��用Maven和Gradle开发项目的�Q�下载就非常�ȝ��Q�下�l�出Spring Framework jar官方直接下蝲路径:

http://repo.spring.io/libs-release-local/org/springframework/spring/

spring 4.0.x(Spring Framework 4.0.5)下蝲

http://repo.spring.io/libs-release-local/org/springframework/spring/4.0.5.RELEASE/spring-framework-4.0.5.RELEASE-dist.zip

spring 3.2.x�Q�Spring Framework 3.2.9�Q�下载：

http://repo.spring.io/libs-release-local/org/springframework/spring/3.2.9.RELEASE/spring-framework-3.2.9.RELEASE-dist.zip

spring 3.2.x�Q�Spring Framework 3.2.4�Q�下载：

http://repo.springsource.org/libs-release-local/org/springframework/spring/3.2.4.RELEASE/spring-framework-3.2.4.RELEASE-dist.zip

另spring security下蝲路径�Q?/p>

http://repo.spring.io/libs-release-local/org/springframework/security/spring-security/

http://repo.spring.io/libs-release-local/org/springframework/security/spring-security/3.2.4.RELEASE/spring-security-3.2.4.RELEASE-dist.zip

天下 2019-02-12 11:44 发表评论

spring源码分析�Q?�Q�AnnotationMethodHandlerAdapter

天下 — Wed, 11 Apr 2018 08:40:00 GMT

public class AnnotationMethodHandlerAdapter extends WebContentGenerator
        implements HandlerAdapter, Ordered, BeanFactoryAware {
    //

    public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        return invokeHandlerMethod(request, response, handler);
    }

    protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        ServletHandlerMethodResolver methodResolver = getMethodResolver(handler);
        Method handlerMethod = methodResolver.resolveHandlerMethod(request);
        ServletHandlerMethodInvoker methodInvoker = new ServletHandlerMethodInvoker(methodResolver);
        ServletWebRequest webRequest = new ServletWebRequest(request, response);
        ExtendedModelMap implicitModel = new BindingAwareModelMap();

        Object result = methodInvoker.invokeHandlerMethod(handlerMethod, handler, webRequest, implicitModel);
        ModelAndView mav =
                methodInvoker.getModelAndView(handlerMethod, handler.getClass(), result, implicitModel, webRequest);
        methodInvoker.updateModelAttributes(handler, (mav != null ? mav.getModel() : null), implicitModel, webRequest);
        return mav;
    }

    public ModelAndView getModelAndView(Method handlerMethod, Class handlerType, Object returnValue,
            ExtendedModelMap implicitModel, ServletWebRequest webRequest) throws Exception {}
}

其他

public final class Method extends Executable {
    public Object invoke(Object obj, Object args)
    throws IllegalAccessException, IllegalArgumentException,InvocationTargetException
    {
        if (!override) {
            if (!Reflection.quickCheckMemberAccess(clazz, modifiers)) {
                Class caller = Reflection.getCallerClass();
                checkAccess(caller, clazz, obj, modifiers);
            }
        }
        MethodAccessor ma = methodAccessor;             // read volatile
        if (ma == null) {
            ma = acquireMethodAccessor();
        }
        return ma.invoke(obj, args);
    }
}
public class ModelMap extends LinkedHashMap<String, Object> {}

public abstract class AbstractView extends WebApplicationObjectSupport implements View, BeanNameAware {
    /**
     * Prepares the view given the specified model, merging it with static
     * attributes and a RequestContext attribute, if necessary.
     * Delegates to renderMergedOutputModel for the actual rendering.
     * @see #renderMergedOutputModel
     */
    @Override
    public void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
        if (logger.isTraceEnabled()) {
            logger.trace("Rendering view with name '" + this.beanName + "' with model " + model +
                " and static attributes " + this.staticAttributes);
        }

        Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
        prepareResponse(request, response);
        renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
    }
}

代码�Q?br />

天下 2018-04-11 16:40 发表评论

spring源码分析�Q?�Q�DispatcherServlet

天下 — Wed, 11 Apr 2018 08:39:00 GMT

public class DispatcherServlet extends FrameworkServlet {
    private List<HandlerMapping> handlerMappings;

    protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
        doDispatch(request, response);
    }

    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;
        try {
            ModelAndView mv = null;
            Exception dispatchException = null;
            try {
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                // Determine handler for the current request.  //映射处理�?/span>
                mappedHandler = getHandler(processedRequest); //HandlerExecutionChain
                if (mappedHandler == null || mappedHandler.getHandler() == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request. //适配处理�?/span>
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                // Actually invoke the handler.
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                applyDefaultViewName(processedRequest, mv);
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }

            //渲染视图
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        finally {
        }
    }
    private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
        HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
        // Did the handler return a view to render?
        if (mv != null && !mv.wasCleared()) {
            render(mv, request, response);
        }
        else {
            if (logger.isDebugEnabled()) {
                logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
                        "': assuming HandlerAdapter completed request handling");
            }
        }
        if (mappedHandler != null) {
            mappedHandler.triggerAfterCompletion(request, response, null);
        }
    }

    protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
        // Determine locale for request and apply it to the response.
        Locale locale = this.localeResolver.resolveLocale(request);
        response.setLocale(locale);

        View view;
        if (mv.isReference()) {
            // We need to resolve the view name.
            view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);
            if (view == null) {
                throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
                        "' in servlet with name '" + getServletName() + "'");
            }
        }
        else {
            // No need to lookup: the ModelAndView object contains the actual View object.
            view = mv.getView();
            if (view == null) {
                throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
                        "View object in servlet with name '" + getServletName() + "'");
            }
        }

        // Delegate to the View object for rendering.
        if (logger.isDebugEnabled()) {
            logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");
        }
        try {
            view.render(mv.getModelInternal(), request, response);
        }
        catch (Exception ex) {
            logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" +    getServletName() + "'", ex);
            throw ex;
        }
}

天下 2018-04-11 16:39 发表评论

AutoCloseable,Closeable和Flushable接口

天下 — Fri, 04 Dec 2015 06:50:00 GMT

探究java IO之AutoCloseable,Closeable和Flushable接口
java-io与网�l�编�E?br />
�?个接口对于流�cȝ��当重要。其中两个接口是Closeable和Flushable�Q�它们是在java.io包中定义的，�q�且是由JDK5��d��的。第3个接口是AutoColseable�Q�它是由JDK7��d��的新接口�Q�被打包到java.lang包中�?br />
AutoCloseable接口对JDK7新添加的带资源的try语句提供了支持，�q�种try语句可以自动执行资源关闭�q�程。只有实��C��AutoCloseable接口的类的对象才可以由带资源的try语句�q�行��理。AutoCloseable接口只定义了close()�Ҏ��Q?br />void close() throws Exception
�q�个�Ҏ��关闭调用对象�Q�释攑֏�能占用的所有资源。在带资源的try语句的末��，会自动调用该�Ҏ��Q�因此消除了昑ּ�调用close()�Ҏ��的需要�?br />
Closeable接口也定义了close()�Ҏ��。实��C��Closeable接口的类的对象可以被关闭。从JDK7开始，Closeable扩展了AutoCloseable。因此，在JDK7中，所有实��C��Closeable接口的类也都实现了AutoCloseable接口�?br />
实现了Flushable接口的类的对象，可以强制��缓存的输出写入��C��对象兌��的流中。该接口定义了flush()�Ҏ��Q�如下所�C�：
void flush() throws IOException
��h��通常会导致缓存的输出被物理地写入到底层设备中。写入流的所有I/O�c�都实现了Flushable接口�?br />
注：关于带资源的try语句�?个关键点�Q?br />
由带资源的try语句��理的资源必��L��实现了AutoCloseable接口的类的对象�?br />
在try代码中声明的资源被隐式声明�ؓfianl�?br />
通过使用分号分隔每个声明可以��理多个资源�?br />
此外误��住，所声明资源的作用域被限制在带资源的try语句中。带资源的try语句的主要优�Ҏ��Q�当try代码块结束时�Q�资源（在此时流�Q�会被自动关闭。因此，不太可能会忘记关闭流。��有带资源的try语句�Q�通常可以使源代码更短�Q�更清晰�Q�更�Ҏ��l�护。如例：

package io;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;

public class InputStreamReaderTest
{
    public static void main(String[] args)
    {
        try(BufferedReader reader = new BufferedReader(
            new InputStreamReader(
                new FileInputStream(
                    new File("/home/fuhd/text")),"UTF8"),1024)){
            System.out.println(reader.readLine());    //�q�里直接��M��?/span>
        } catch(IOException e){
            e.printStackTrace();
        }
    }
}

天下 2015-12-04 14:50 发表评论

JAVA通过JNI调用本地dll

天下 — Fri, 04 Dec 2015 03:48:00 GMT

JAVA通过JNI调用本地dll

一、JAVA中所需要做的工�?nbsp;
Java工程Example01
�W�一步：创徏Java�c�，�c�d��Q�TestJni 在里面定义一个本地方法（用native关键字修饰的�Ҏ��Q?br />package NeoWay;
public class TestJni
{
    static {
            System.loadLibrary("neoway");
    }
    public native static void sayHello();
}

�W�二步：生成javah 说需要的.class文�g
在DOS�H�口中进入工�E�所在的src文�g�?
javac NeoWay\TestJni.java

�W�三步：使用javah命��o生成本地�Ҏ��的C++头文�?nbsp;
@rem javah �?�c?br />javah NeoWay.TestJni
在DOS�H�口中进入工�E�所在目录，然后执行javah NeoWay.TestJni命��o�Q�执行完之后��׃��在当前目录生成一个后�~�名�ؓ.h的头文�g

�W�四步：新徏VC++的dll工程�Q�附仉��项�Q�空��目�Q�，工程名�ؓ�Q�neoway
��相关的路径加入VC++的include
C:\Program Files\Java\jdk1.7.0_80\include
C:\Program Files\Java\jdk1.7.0_80\include\Win32
��生成的NeoWay_TestJni.h引入该VC工程

NeoWay_TestJni.h内容如下�Q?br />/* DO NOT EDIT THIS FILE - it is machine generated */
#include
/* Header for class NeoWay_TestJni */

#ifndef _Included_NeoWay_TestJni
#define _Included_NeoWay_TestJni
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class:     NeoWay_TestJni
* Method:    sayHello
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_NeoWay_TestJni_sayHello
  (JNIEnv *, jclass);

#ifdef __cplusplus
}
#endif
#endif

新徏一�?nbsp;NeoWay_TestJni.cpp�Q�内容如下：
#include "NeoWay_TestJni.h"
JNIEXPORT void JNICALL Java_NeoWay_TestJni_sayHello (JNIEnv *, jclass)
{
    printf("Java_NeoWay_TestJni_sayHello() Entry\r\n");
}

//Example01
import NeoWay.TestJni;
public class Example01
{
    public static void main(String[] args)
    {
        System.out.println("main() entry()");
        TestJni.sayHello();
    }
}

�W�五步：��试�q�行
��VC++工程生成neoway.dll拯��至Java工程Example01目录
javac Example01.java
java Example01

输出�Q?br />main() entry()
Java_NeoWay_TestJni_sayHello() Entry

天下 2015-12-04 11:48 发表评论

Java�U�程Example

天下 — Thu, 03 Dec 2015 06:07:00 GMT

//NewThread.java
package NewThread;

public class NewThread implements Runnable
{
    public String name;
    public Thread t;
    public NewThread(String _name)
    {
        name = _name;
        t = new Thread(this);
        t.start();
    }

    public void run() {
        for (int i=0;i<3;i++)
        {
            try {
                //有可能被其他�U�程中断
                Thread.sleep(1000);
            }
            catch(Exception e) {
            }
            System.out.println(name+i);
        }

    }
}

import NewThread.NewThread;

public class Example01
{
    public static void main(String[] args)
    {
        NewThread t = new NewThread("NewThread");
        try {
            t.t.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("main_thread.join()");
    }
}

天下 2015-12-03 14:07 发表评论

Java和C++的不同点

天下 — Thu, 14 Mar 2013 07:59:00 GMT

Java 定义�?4 �U�整数类型：byte、short、int �?long�?/span>

所有这些类型都是有�W�号的、正的或负的整数�?/span>

Java 不支持无�W�号的、只是正值的整数。许多其他计��机语言同时支持有符号和无符��h��数。然而，Java 的设计者觉得无�W�号整数不是必需的�?/span>

�?Java 中，用于存储字符的数据类型是 char。然而，C/C++�E�序员要当心�Q?/span>

Java 中的 char�?C �?C++中的 char 是不同的。在 C/C++中，char 的宽度是 8 位。而在 Java 中不是这��L��?/span>

相反�Q�Java 使用 Unicode 表示字符。�ؓ此，Unicode 需�?16 位宽。因此，�?Java �?char �?16 位类型�?span style="white-space: pre">

�?JDK 7 开始，可以使用二进制指定整型字面倹{��ؓ此，使用 0b �?0B 作�ؓ数值的前缀�?/span>

�?JDK 7 开始，在整型字面��g��q�可以嵌入一个或多个下划�Uѝ��嵌入下划线可以佉K��d��大的整数变得更加�Ҏ��。当�~�译字面值时�Q�会丢弃下划�Uѝ�?span style="white-space: pre">

int x = 123___456___789;

int x = 0b1101_0101_0001_1010;

Java 中的字符被烦引到 Unicode 字符集，它们是可以�{换成整数�?16 位��|��q�且可以使用整数�q�算�W�进行操作，例如加和减运��符。字�W�型字面��g��用位于一对单引号中的字符来表�C��?/span>

所有可见的 ASCII 字符都可以直接输入到单引号中�Q�如'a'�?z'以及'@'。对于那些不能直接输入的字符�Q�可以��用�{义字�W�序列输入需要的字符�Q?/span>

例如'\"表示单引受��?\n'表示换行�W�。还有一�U�以八进制或十六�q�制直接输入字符值的机制。对于八�q�制表示法，使用反斜杠后跟三位数字表�C�，

例如'\141'是字�?a'。对于十六进�Ӟ��先输�?#8220;\u”�Q�然后是 4 位的十六�q�制数�?/span>

例如'\u0061'表示 ISO-Latin-1 字符'a'�Q�因为第一个字节�ؓ 0�Q?\u73b0'�?'�?

char c = '\u73b0'; //�?/span>

无符号右�U�运��符

int i=-8>>>1;

Java不用goto语句,而是用try-catch-finally异常处理语句来代替goto语句处理出错的功�?

Java不支持宏定义,而是使用关键字final来定义常�?在C++中则采用宏定义来实现帔R��定义,�q�不得于�E�序的可��L�?

�l�构和联合的处理.在C和C++�?�l�构和联合的所有成员均为公�?�q�就带来了安全性问�?而在Java中根本就不包含结构和联合,所有的内容都封装在�c�里�?/span>

Java不再使用指针.�E�序员不能直接进行�Q何指针操�?

java没有象C++一��L��操作�W�重载机�?span style="white-space: pre">

java不管构造函数有无参�?都应该写括号

java初始化成员变量的�Ҏ��和C�Q�＋有很大不�? java允许直接在类内部指定成员变量初始�?span style="white-space: pre">

java成员变量的初始化��序取决于成员变量的声明��序, 而成员变量的初始化��L��早于构造函数的执行.�q�也和C�Q�＋有很大不�?C�Q�＋的成员变量初始化��序也取决于成员变量的声明顺�?但是,它们只能在构造函��C��?或者在构造函数的初始化列表里�q�行初始�?而不会先于构造函�?span style="white-space: pre">

Java�E�序中所有的对象都是用new操作�W�徏立在内存堆栈�?/span>

Java提供了自动化的垃圾搜�?可以手动触发)。没有析构函式的概念�Q�对 finalize() 的��用是不推荐的

Java没有函式指标机制。替代的概念是接口，Adapter �?Listener也是被广泛��用的

Java的��承是面向对象�E�序设计的关键。在Java中，通过关键字extends�l�承一个已有的�c�，被��承的�cȝ��为父�c?��类�Q�基�c?�Q�新的类�U�Cؓ子类(�z��c?。在Java中不允许多��ѝ�?/span>

Java中，this通常指当前对象，super则指父类的�?/span>

Java里面有一个金�U�玉律：��M��public非static函数的调用都是多态的�?所以，super.method()必然调用的是子类的那个版�?/span>

天下 2013-03-14 15:59 发表评论