Java – 第2页 – California Sunshine

使用Java Dynamic Proxy API实现简单的Function Decorator

Python里有非常方便的Function Decorator语法糖，使用起来非常简便。如果想在Java里做类似的事情，可以使用Dynamic Proxy API来实现。

看看这个小例子。有一组Web服务接口，需要访问数据库得到所需的数据。比如，

Analyzer analyzer = new Analyzer(...);
...
// 使用了Spark Framework
Spark.get("/review_request_per_month_last_half_year", (req, res) -> {
      return analyzer.getRequestStatisticOfLastSixMonth();
});

Analyzer analyzer = new Analyzer(...);

...

// 使用了Spark Framework

Spark.get("/review_request_per_month_last_half_year", (req, res) -> {

return analyzer.getRequestStatisticOfLastSixMonth();

});

代码里的Analyzer类会去数据库找到相应的数据。

为了提高访问的效率，加入memcached，在真正的数据库访问之前，先去查看有没有相应的Cache，代码会变成类似的样子，

String result = memcachedClient.get("review_request_per_month_last_half_year");
if (result == null) {
      result = review_request_per_month_last_half_year;
      memcachedClient.set("review_request_per_month_last_half_year", result);
}
return result;

String result = memcachedClient.get("review_request_per_month_last_half_year");

if (result == null) {

result = review_request_per_month_last_half_year;

memcachedClient.set("review_request_per_month_last_half_year", result);

}

return result;

如果每个服务接口都要做同样的事，可想而知，会有非常多的重复代码。这时就可以利用Dynamic Proxy API来大大的优化代码实现，非常灵活。

Dynamic Proxy API只能针对接口，所以要为原来Analyzer类写一个接口类，如：

interface IAnalyzer {
   String getRequestStatisticOfLastSixMonth();
}

class Analyzer implements IAnalyzer {

  @Override
  public String getRequestStatisticOfLastSixMonth() {
      // ....
  }

}

interface IAnalyzer {

String getRequestStatisticOfLastSixMonth();

}

class Analyzer implements IAnalyzer {

@Override

public String getRequestStatisticOfLastSixMonth() {

// ....

}

然后我们的代理实现类要继承自InvocationHandler，并通过Proxy.newProxyInstance生成真正的代理。看下面的实现，

public class CachedAnalyzerProxy implements InvocationHandler {

  private static final Logger LOGGER = LogManager.getLogger(CachedAnalyzerProxy.class);

  private IAnalyzer analyzer;

  private final MemcachedUtil cached = new MemcachedUtil("localhost", "11211");

  public CachedAnalyzerProxy(IAnalyzer analyzer) {
    // 保留Analyzer实现
    this.analyzer = analyzer;
  }

  public static IAnalyzer bind(IAnalyzer analyzer) {
    // 生成真正的动态代理
    return (IAnalyzer) Proxy.newProxyInstance(
        analyzer.getClass().getClassLoader(), new Class[] { IAnalyzer.class }, new CachedAnalyzerProxy(analyzer));
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    // 这里的Cache Key简单的使用的函数名
    LOGGER.debug("invoking " + method.getName());
    String result = cached.get(method.getName());
    if (result == null) {
      LOGGER.debug("cache is not hit.");
      // 利用保留的Analyzer引用，调用原来的函数实现
      result = (String) method.invoke(analyzer, args);
      cached.set(method.getName(), result);
    } else {
      LOGGER.debug("cache is hit");
    }
    return result;
  }
}

public class CachedAnalyzerProxy implements InvocationHandler {

private static final Logger LOGGER = LogManager.getLogger(CachedAnalyzerProxy.class);

private IAnalyzer analyzer;

private final MemcachedUtil cached = new MemcachedUtil("localhost", "11211");

public CachedAnalyzerProxy(IAnalyzer analyzer) {

// 保留Analyzer实现

this.analyzer = analyzer;

}

public static IAnalyzer bind(IAnalyzer analyzer) {

// 生成真正的动态代理

return (IAnalyzer) Proxy.newProxyInstance(

analyzer.getClass().getClassLoader(), new Class[] { IAnalyzer.class }, new CachedAnalyzerProxy(analyzer));

}

@Override

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

// 这里的Cache Key简单的使用的函数名

LOGGER.debug("invoking " + method.getName());

String result = cached.get(method.getName());

if (result == null) {

LOGGER.debug("cache is not hit.");

// 利用保留的Analyzer引用，调用原来的函数实现

result = (String) method.invoke(analyzer, args);

cached.set(method.getName(), result);

} else {

LOGGER.debug("cache is hit");

}

return result;

}

有了动态代理，原来Web服务接口的实现就非常简洁了。

IAnalyzer analyzer = CachedAnalyzerProxy.bind(new Analyzer());

Spark.get("/review_request_per_month_last_half_year", (req, res) -> {
        return analyzer.getRequestStatisticOfLastSixMonth();
});

IAnalyzer analyzer = CachedAnalyzerProxy.bind(new Analyzer());

Spark.get("/review_request_per_month_last_half_year", (req, res) -> {

return analyzer.getRequestStatisticOfLastSixMonth();

});

Java自带的Dynamic Proxy API虽然有些限制，但使用起来还是非常简单的。听说还有更强大的CGLib，有机会现研究一下。😄

Eclipse里生成Guava-based的hashCode()和equals()

做Java开发的常常要重写类的hashCode()和equals()。一般情况下，可以套常用的模板。Eclipse就套用这些模板，直接生成默认实现，可实现比较冗长，比如下面的例子

有类A，

public class A {

	private int a;
	
	private double b;
	
	private String c;
	
}

public class A {

private int a;

private double b;

private String c;

}

Eclipse的默认实现是这样的，

public class A {

	private int a;
	
	private double b;
	
	private String c;

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + a;
		long temp;
		temp = Double.doubleToLongBits(b);
		result = prime * result + (int) (temp ^ (temp >>> 32));
		result = prime * result + ((c == null) ? 0 : c.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		A other = (A) obj;
		if (a != other.a)
			return false;
		if (Double.doubleToLongBits(b) != Double.doubleToLongBits(other.b))
			return false;
		if (c == null) {
			if (other.c != null)
				return false;
		} else if (!c.equals(other.c))
			return false;
		return true;
	}
	
}

public class A {

private int a;

private double b;

private String c;

@Override

public int hashCode() {

final int prime = 31;

int result = 1;

result = prime * result + a;

long temp;

temp = Double.doubleToLongBits(b);

result = prime * result + (int) (temp ^ (temp >>> 32));

result = prime * result + ((c == null) ? 0 : c.hashCode());

return result;

}

@Override

public boolean equals(Object obj) {

if (this == obj)

return true;

if (obj == null)

return false;

if (getClass() != obj.getClass())

return false;

A other = (A) obj;

if (a != other.a)

return false;

if (Double.doubleToLongBits(b) != Double.doubleToLongBits(other.b))

return false;

if (c == null) {

if (other.c != null)

return false;

} else if (!c.equals(other.c))

return false;

return true;

}

显然实现比较冗长，也比较乱，包含了很多细节，有些也不符合代码规范（比如if后没有花括号）。

用过Guava的同学都知道，使用Objects类可以大大简化这两个函数的实现。我试着扩展了Eclipse JDT，套用Guava的实现模板，那代码就漂亮多了。Guava隐藏了大量的实现细节。

如下，

public class A {

	private int a;
	
	private double b;
	
	private String c;

	@Override
	public int hashCode() {
	  return Objects.hashCode(a, b, c);
	}

	@Override
	public boolean equals(Object obj) {
	  if (obj == this) {
	    return true;
	  }
	  
	  if (!(obj instanceof A)) {
	      return false;
	  }
	  
	  A anotherInstance = (A) obj;
	  return Objects.equal(anotherInstance.a, this.a)
	      && Objects.equal(anotherInstance.b, this.b)
	      && Objects.equal(anotherInstance.c, this.c);
	}
	
}

public class A {

private int a;

private double b;

private String c;

@Override

public int hashCode() {

return Objects.hashCode(a, b, c);

}

@Override

public boolean equals(Object obj) {

if (obj == this) {

return true;

}

if (!(obj instanceof A)) {

return false;

}

A anotherInstance = (A) obj;

return Objects.equal(anotherInstance.a, this.a)

&& Objects.equal(anotherInstance.b, this.b)

&& Objects.equal(anotherInstance.c, this.c);

}

具体的代码实现在Github上，点这。

主要分如下有几步，

Project Explorer的上下文菜单中加入新的功能选项。
通过Eclipse里事件得到Java CompliationUnit，使用ASTParser得到类里的Non-Static Member Field，然后就套用新模板吧。
一个源文件中可能包含多个Java Class，所以还要有个Dialog来选择在哪个类中实现方法。

其他细节都在代码里的，有兴趣的就看看吧。😁

聊聊ClassLoader in Java World

ClassLoader是Java技术中非常主要的概念，原因是它用来加载Java Class。如果没有Class，也就没有对象；没有对象，就没有之后的一切了。

Java ClassLoader的默认实现是一种双亲结构，即总是尝试让Parent ClassLoader加载类。这样有一些优点，当然也有很大的限制，比如就不利于不同Module对多版本类的加载。更多的细节，在下面我做的PPT里。

Let's talk about java class loader from Yongqiang Li

还有些新的理解和发现。

自定义的ClassLoader可以把Parent ClassLoader设置为null，如果再把loadClass函数重写，就可以完全屏蔽default classLoader的影响。如OSGi的Bundle ClassLoader的最终的Parent就不是Bootstrap ClassLoader（Bundle ClassLoader的实现还是会去从默认ClassLoader去加载java.*的类）。
程序执行时，ClassLoader的选择。做几个小实验你就会发现，默认的ClassLoader是“加载当前执行函数所在类的ClassLoader”。在OpenJDK的源码中一通Search，就可以找到一些端倪。

在源文件src\interp\engine\interp.c中，有executeJava()函数中，执行ByteCode之前，先准备了MethodBlock的指针，它中间

uintptr_t *executeJava() {
    ...

    uintptr_t *arg1;
    register CodePntr pc;
    ExecEnv *ee = getExecEnv();
    Frame *frame = ee-&gt;last_frame;
    register uintptr_t *lvars = frame-&gt;lvars;
    register uintptr_t *ostack = frame-&gt;ostack;

    Object *this = (Object*)lvars[0];
    <strong>MethodBlock *new_mb, *mb = frame-&gt;mb;</strong>
    ConstantPool *cp = &amp;(CLASS_CB(mb-&gt;class)-&gt;constant_pool);

uintptr_t *executeJava() {

...

uintptr_t *arg1;

ExecEnv *ee = getExecEnv();

Frame *frame = ee->last_frame;

Object *this = (Object*)lvars[0];

MethodBlock *new_mb, *mb = frame->mb;

ConstantPool *cp = &(CLASS_CB(mb->class)->constant_pool);

可以看看GETSTATIC这个指令的实现（此指令会在读取类的静态方法时调用）。可以看到resolveField()方法，并在mb的Class指针传入。idx是Static Field对应Constant Pool里的index。

... 

DEF_OPC_RW(OPC_GETSTATIC, ({
        int idx, cache, opcode;
        FieldBlock *fb;
        Operand operand;
               
        WITH_OPCODE_CHANGE_CP_DINDEX(OPC_GETSTATIC, idx, cache);

        frame-&gt;last_pc = pc;
        <strong>fb = resolveField(mb-&gt;class, idx);</strong>

        if(fb != NULL)
            initClass(fb-&gt;class);

        if(exceptionOccurred0(ee))
            goto throwException;

        if((*fb-&gt;type == 'J') || (*fb-&gt;type == 'D'))
            opcode = OPC_GETSTATIC2_QUICK;
        else
            if(*fb-&gt;type == 'L' || *fb-&gt;type == '[')
                opcode = OPC_GETSTATIC_QUICK_REF;
            else
                opcode = OPC_GETSTATIC_QUICK;

        operand.pntr = fb;
        OPCODE_REWRITE(opcode, cache, operand);

        REDISPATCH
    });)

...

...

DEF_OPC_RW(OPC_GETSTATIC, ({

int idx, cache, opcode;

FieldBlock *fb;

Operand operand;

WITH_OPCODE_CHANGE_CP_DINDEX(OPC_GETSTATIC, idx, cache);

frame->last_pc = pc;

fb = resolveField(mb->class, idx);

if(fb != NULL)

initClass(fb->class);

if(exceptionOccurred0(ee))

goto throwException;

if((*fb->type == 'J') || (*fb->type == 'D'))

opcode = OPC_GETSTATIC2_QUICK;

else

if(*fb->type == 'L' || *fb->type == '[')

opcode = OPC_GETSTATIC_QUICK_REF;

else

opcode = OPC_GETSTATIC_QUICK;

operand.pntr = fb;

OPCODE_REWRITE(opcode, cache, operand);

REDISPATCH

});)

...

resolveField中被调用resolveClass函数

FieldBlock *resolveField(Class *class, int cp_index) {
    ConstantPool *cp = &amp;(CLASS_CB(class)-&gt;constant_pool);
    FieldBlock *fb = NULL;

retry:
    switch(CP_TYPE(cp, cp_index)) {
        ...
        
        case CONSTANT_Fieldref: {
            Class *resolved_class;
            char *fieldname, *fieldtype;
            int cl_idx = CP_FIELD_CLASS(cp, cp_index);
            int name_type_idx = CP_FIELD_NAME_TYPE(cp, cp_index);

            MBARRIER();
            if(CP_TYPE(cp, cp_index) != CONSTANT_Fieldref)
                goto retry;

            fieldname = CP_UTF8(cp, CP_NAME_TYPE_NAME(cp, name_type_idx));
            fieldtype = CP_UTF8(cp, CP_NAME_TYPE_TYPE(cp, name_type_idx));
            <strong>resolved_class = resolveClass(class, cl_idx, TRUE, FALSE);</strong>

            ...

            break;
        }
    }
 
    return fb;
}

FieldBlock *resolveField(Class *class, int cp_index) {

ConstantPool *cp = &(CLASS_CB(class)->constant_pool);

FieldBlock *fb = NULL;

retry:

switch(CP_TYPE(cp, cp_index)) {

...

case CONSTANT_Fieldref: {

Class *resolved_class;

char *fieldname, *fieldtype;

int cl_idx = CP_FIELD_CLASS(cp, cp_index);

int name_type_idx = CP_FIELD_NAME_TYPE(cp, cp_index);

MBARRIER();

if(CP_TYPE(cp, cp_index) != CONSTANT_Fieldref)

goto retry;

fieldname = CP_UTF8(cp, CP_NAME_TYPE_NAME(cp, name_type_idx));

fieldtype = CP_UTF8(cp, CP_NAME_TYPE_TYPE(cp, name_type_idx));

resolved_class = resolveClass(class, cl_idx, TRUE, FALSE);

...

break;

}

return fb;

}

resolveClass又回调用findClassFromClass（其实是个Macro），同样传入class指针。看看Macro的定义，就可以很清楚了。

#define findClassFromClass(classname, class)                               \
    (CLASS_CB(class)->name == classname ? class :                          \
        findClassFromClassLoader(classname, CLASS_CB(class)->class_loader))

#define findClassFromClass(classname, class) \

(CLASS_CB(class)->name == classname ? class : \

findClassFromClassLoader(classname, CLASS_CB(class)->class_loader))

是从ClassBlock结构中找到对应的ClassLoader.

其实记住这个结论就好。这样就可以完全打错传统的ClassLoader的限制，比如OSGi Plugin/Bundle里的所有类就是由OSGi自己的加载器加载的，非常灵活，可以实现非常牛逼的功能！

在单元测试中使用PowerMockito隔离static native method

在单元测试中，如果被测类使用了某些static native接口，会使测试不太好写，因为Native API需要装载某使用Native库。我们可以使用强大的PowerMockito对这些接口进行隔离。

下面是个小例子。

Class with Native Static Method

package org.yli.test;

/**
 * Created by yli on 10/2/2015.
 */
public class NativeClass {

  public static native int doAdd(int a, int b);

  public static native int doSub(int a, int b);

}

package org.yli.test;

/**

* Created by yli on 10/2/2015.

public class NativeClass {

public static native int doAdd(int a, int b);

public static native int doSub(int a, int b);

}

Class which consumes the native static methods

package org.yli.test;

/**
 * Created by yli on 10/2/2015.
 */
public class Consumer {

  public int add(int a, int b) {
    return NativeClass.doAdd(a, b);
  }

  public int sub(int a, int b) {
    return NativeClass.doSub(a, b);
  }

}

package org.yli.test;

/**

* Created by yli on 10/2/2015.

public class Consumer {

public int add(int a, int b) {

return NativeClass.doAdd(a, b);

}

public int sub(int a, int b) {

return NativeClass.doSub(a, b);

}

Unit Test

Mock了Static Native方法，并做了Verify.

package org.yli.test;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

import static org.junit.Assert.assertEquals;
import static org.powermock.api.mockito.PowerMockito.when;

/**
 * Created by yli on 10/2/2015.
 */
@RunWith(PowerMockRunner.class)
@PrepareForTest(NativeClass.class)
public class ConsumerTest {

  @Test
  public void testAdd() {
    PowerMockito.mockStatic(NativeClass.class);
    when(NativeClass.doAdd(1, 2)).thenReturn(3);

    Consumer consumer = new Consumer();
    assertEquals(3, consumer.add(1, 2));

    PowerMockito.verifyStatic();
    NativeClass.doAdd(1, 2);
  }

  @Test
  public void testSub() {
    PowerMockito.mockStatic(NativeClass.class);
    when(NativeClass.doSub(1, 2)).thenReturn(-1);

    Consumer consumer = new Consumer();
    assertEquals(-1, consumer.sub(1, 2));

    PowerMockito.verifyStatic();
    NativeClass.doSub(1, 2);
  }

}

package org.yli.test;

import org.junit.Test;

import org.junit.runner.RunWith;

import org.powermock.api.mockito.PowerMockito;

import org.powermock.core.classloader.annotations.PrepareForTest;

import org.powermock.modules.junit4.PowerMockRunner;

import static org.junit.Assert.assertEquals;

import static org.powermock.api.mockito.PowerMockito.when;

/**

* Created by yli on 10/2/2015.

@RunWith(PowerMockRunner.class)

@PrepareForTest(NativeClass.class)

public class ConsumerTest {

@Test

public void testAdd() {

PowerMockito.mockStatic(NativeClass.class);

when(NativeClass.doAdd(1, 2)).thenReturn(3);

Consumer consumer = new Consumer();

assertEquals(3, consumer.add(1, 2));

PowerMockito.verifyStatic();

NativeClass.doAdd(1, 2);

}

@Test

public void testSub() {

PowerMockito.mockStatic(NativeClass.class);

when(NativeClass.doSub(1, 2)).thenReturn(-1);

Consumer consumer = new Consumer();

assertEquals(-1, consumer.sub(1, 2));

PowerMockito.verifyStatic();

NativeClass.doSub(1, 2);

}

这只是个简单的例子，实际运用中Native方法往往比较复杂。在写单元测试时应该明确被测的对象，把不必要的接口Mock起来，会使测试变得非常清晰。

PS: 此例的Maven dependencies

junit:junit:4.8.1
org.powermock:powermock-mockito-release-full:1.6.2

别忘了在RCP App中配置自己的Keybinding Scheme！

在Eclipse RCP的基础上开发，我们会感到非常便利，有好多可重用的组件。但有时也有些意想不到的问题, Key bindings就是其中之一。

一般情况下，我们通过扩展org.eclipse.ui.bindings来增加新的快捷键绑定。下面的例子中，我设置了一个CTRL+T的快捷键。

乍看上去，编译使用都能够做良好，问题出在schemeId上。org.eclipse.ui.defaultAcceleratorConfiguration是默认的scheme, 它里面其实包含了大量的快捷键设定，很多可能是你不要的，比如CTRL+F（查找与替换），CTRL+N（新建Wizard）等等。如果发布到产品中，反而画蛇添足。

修正这个问题很容易，就是设置自己的scheme。下面是个例子，

别忘要同时修改一下，Key的设定，

还有如果要让自定义的scheme能生效，要修改一下plugin_customization.ini文件，加入如下配置，

org.eclipse.ui/KEY_CONFIGURATION_ID=myscheme

1	org.eclipse.ui/KEY_CONFIGURATION_ID=myscheme

这样，你的Scheme就会生效了。

可能你回问，如果想重用如CTRL+S的快捷键怎么办？那就重用File Save的commandId，如下，

这样问题就解决了。

制作本地Eclipse Release P2 Repository

因为某些原因，公司的Build Server都不能访问外网了，所以不能直接从Eclipse的公共服务器上下载开发包。以前Eclipse提供所谓All-in-One package，可现在没有了。还有更方便的做法，可以下载Eclipse的所有Pacakge，生成本地的P2 Repository。

Repository包含metadata和artifact，要分别下载，但可以下载到同一个文件下。

C:\dev_app\EclipseLuna\eclipse>eclipse.exe -nosplash -verbose -application org.eclipse.equinox.p2.artifact.repository.mirrorApplication -source http://download.eclipse.org/releases/luna/ -destination file:c:/dev_app/luna_app

1	C:\dev_app\EclipseLuna\eclipse>eclipse.exe -nosplash -verbose -application org.eclipse.equinox.p2.artifact.repository.mirrorApplication -source http://download.eclipse.org/releases/luna/ -destination file:c:/dev_app/luna_app

C:\dev_app\EclipseLuna\eclipse>eclipse.exe -nosplash -verbose -application org.eclipse.equinox.p2.metadata.repository.mirrorApplication -source http://download.eclipse.org/releases/luna/ -destination file:c:/dev_app/luna_app

1	C:\dev_app\EclipseLuna\eclipse>eclipse.exe -nosplash -verbose -application org.eclipse.equinox.p2.metadata.repository.mirrorApplication -source http://download.eclipse.org/releases/luna/ -destination file:c:/dev_app/luna_app

程序运行后，没有UI，只在后台下载。耐心等待下载完成后，程序自动退出，所有的包就在destination里了。如果需要，可以传到Sonatype Nexus做成Virtual Repository （详见在Nexus OSS上建Eclipse p2 repository）。

NOTE

完整的Repository非常大，下载的过程很长，一次下载不完可以分多次下载，重新键入命令即可，下载完成的包都很跳过的。
下载artifact时，会有一个.blobstore文件夹，不要以为它是个临时文件夹，它也是Repository的一部分。

Reference

正则表达式的动态替换

Java中的String类提供了replaceAll和replaceFirst方法，用来识别符合正则表达式的substring，并全局替换和只替换第一个substring。

但有时情况会更复杂一些。比如转换input string中所有的floating number的单位，从厘米转换为米。这时，之前的函数就帮不上忙了，我们要使用Java Regex其他类的更强大功能。

看看下面的例子。

public class UnitConverter {
  private static final Pattern FLOATING_REGEX_PATTERN = Pattern.compile("[-+]?[0-9]*\\.?[0-9]+([eE][-+]?[0-9]+)?");
  
  private static String convert(String input) {
    Matcher matcher = FLOATING_REGEX_PATTERN.matcher(input);
    StringBuffer sb = new StringBuffer();

    while (matcher.find()) {
      // 转换匹配上的floating number
      matcher.appendReplacement(sb, Double.toString(Double.valueOf(matcher.group(0) / 100.0)));
    }
    // 加上Tail的部分
    matcher.appendTail(sb);

    return sb.toString();
  }

public class UnitConverter {

private static final Pattern FLOATING_REGEX_PATTERN = Pattern.compile("[-+]?[0-9]*\\.?[0-9]+([eE][-+]?[0-9]+)?");

private static String convert(String input) {

Matcher matcher = FLOATING_REGEX_PATTERN.matcher(input);

StringBuffer sb = new StringBuffer();

while (matcher.find()) {

// 转换匹配上的floating number

matcher.appendReplacement(sb, Double.toString(Double.valueOf(matcher.group(0) / 100.0)));

}

// 加上Tail的部分

matcher.appendTail(sb);

return sb.toString();

}

下面是Test cases。

  @Test
  public void testCmStringTommString() {
    assertEquals("1.0, 2.0", UnitConverter.convert("100.0, 200.0"));
    assertEquals("0.0, 0.0", UnitConverter.convert("0.0, 0.0"));
    assertEquals("1.0, abc", UnitConverter.convert("100.0, abc"));
    assertEquals("abc, 1.0, def", UnitConverter.convert("abc, 100.0, def"));
    assertEquals("abc, def", UnitConverter.convert("abc, def"));
    assertEquals("1.2, 2.3", UnitConverter.convert("1.2e2, 2.3e2"));
    assertEquals("1.2-3.1:6.0, 2.3", UnitConverter.convert("1.2e2-310.0:600, 2.3e3"));
    assertEquals("-1.2, -2.3", UnitConverter.convert("-1.2e2, -230"));
  }

@Test

public void testCmStringTommString() {

assertEquals("1.0, 2.0", UnitConverter.convert("100.0, 200.0"));

assertEquals("0.0, 0.0", UnitConverter.convert("0.0, 0.0"));

assertEquals("1.0, abc", UnitConverter.convert("100.0, abc"));

assertEquals("abc, 1.0, def", UnitConverter.convert("abc, 100.0, def"));

assertEquals("abc, def", UnitConverter.convert("abc, def"));

assertEquals("1.2, 2.3", UnitConverter.convert("1.2e2, 2.3e2"));

assertEquals("1.2-3.1:6.0, 2.3", UnitConverter.convert("1.2e2-310.0:600, 2.3e3"));

assertEquals("-1.2, -2.3", UnitConverter.convert("-1.2e2, -230"));

}

Google Guava之Immutable Collection

Guava提供了很多Immutable Collection, 包括Set，Map，List等，使用起来简单方便，看看下面的例子。

import java.util.HashMap;
import java.util.Map;
 
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.ImmutableSortedMap;
import com.google.common.collect.ImmutableSortedSet;
 
 
public class TryImmutableMap {
 
    public static void main(String[] args) {
 
        Map<String, String> map = new HashMap<String, String>();
        map.put("abc", "def");
        map.put("def", "efg");
 
        // a immutable map is cloned from a regular map.
        ImmutableMap<String, String> aImmutalbeMap = ImmutableSortedMap.<String, String>copyOf(map);
 
        //aImmutalbeMap.put("tgh", "ihg"); // Exception!! You can't change it.
        //aImmutalbeMap.clear();            // Exception!! You can't change it.
        //aImmutalbeMap.remove("abc");        // Exception!! You can't change it.
 
        System.out.println(aImmutalbeMap.containsKey("abc")); // this line is ok.
 
        // for immutable set
        ImmutableSet<String> immutableSet = ImmutableSortedSet.<String>of("abc", "def", "efg");
        System.out.println(immutableSet); // output: [abc, def, efg]
 
        // for small immutable map
        ImmutableMap<String, String> immutableMap = ImmutableSortedMap.<String, String>of("abc", "def");
        System.out.println(immutableMap); // output: {abc=def}
 
    }
 
}

import java.util.HashMap;

import java.util.Map;

import com.google.common.collect.ImmutableMap;

import com.google.common.collect.ImmutableSet;

import com.google.common.collect.ImmutableSortedMap;

import com.google.common.collect.ImmutableSortedSet;

public class TryImmutableMap {

public static void main(String[] args) {

Map<String, String> map = new HashMap<String, String>();

map.put("abc", "def");

map.put("def", "efg");

// a immutable map is cloned from a regular map.

ImmutableMap<String, String> aImmutalbeMap = ImmutableSortedMap.<String, String>copyOf(map);

//aImmutalbeMap.put("tgh", "ihg"); // Exception!! You can't change it.

//aImmutalbeMap.clear(); // Exception!! You can't change it.

//aImmutalbeMap.remove("abc"); // Exception!! You can't change it.

System.out.println(aImmutalbeMap.containsKey("abc")); // this line is ok.

// for immutable set

ImmutableSet<String> immutableSet = ImmutableSortedSet.<String>of("abc", "def", "efg");

System.out.println(immutableSet); // output: [abc, def, efg]

// for small immutable map

ImmutableMap<String, String> immutableMap = ImmutableSortedMap.<String, String>of("abc", "def");

System.out.println(immutableMap); // output: {abc=def}

}

Google Guava之BiMap

今天介绍一个BiMap的小例子。

import com.google.common.collect.BiMap;
import com.google.common.collect.HashBiMap;
 
 
public class TryBiMap {
 
    public static void main(String[] args) {
        BiMap<String, String> aBiMap = HashBiMap.<String, String>create();
 
        aBiMap.put("abc", "def");
        aBiMap.put("defe", "abcd");
 
        System.out.println(aBiMap); // output: {abc=def, defe=abcd}
        System.out.println(aBiMap.get("abc")); // output: def
 
        // this line will throw a runtime exception
        // because there is "defe":"abcd" already. This record impacts BiMap.inverse.
        // aBiMap.put("abc", "abcd");
 
        // But we can use BiMap.forcePut to put the record of "abc":"abcd"
        // And the record "defe":"abcd" will be erased.
        aBiMap.forcePut("abc", "abcd");
 
        // Use BiMap.inverse() to get a inversed bimap.
        aBiMap = aBiMap.inverse();
 
        System.out.println(aBiMap); // output: {abcd=abc}
        System.out.println(aBiMap.get("abcd")); // output: abc
    }
}

import com.google.common.collect.BiMap;

import com.google.common.collect.HashBiMap;

public class TryBiMap {

public static void main(String[] args) {

BiMap<String, String> aBiMap = HashBiMap.<String, String>create();

aBiMap.put("abc", "def");

aBiMap.put("defe", "abcd");

System.out.println(aBiMap); // output: {abc=def, defe=abcd}

System.out.println(aBiMap.get("abc")); // output: def

// this line will throw a runtime exception

// because there is "defe":"abcd" already. This record impacts BiMap.inverse.

// aBiMap.put("abc", "abcd");

// But we can use BiMap.forcePut to put the record of "abc":"abcd"

// And the record "defe":"abcd" will be erased.

aBiMap.forcePut("abc", "abcd");

// Use BiMap.inverse() to get a inversed bimap.

aBiMap = aBiMap.inverse();

System.out.println(aBiMap); // output: {abcd=abc}

System.out.println(aBiMap.get("abcd")); // output: abc

}

Google Guava之Ordering

Guava提供的Ordering比Comparator强大很多，使用起来非常灵活。下面是个小例子。

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
 
import com.google.common.base.Function;
import com.google.common.collect.Ordering;
 
 
public class TryOrdering {
 
    public static class A implements Comparable<A> {
        int a = 1;
        int b = 2;
 
        public A(int a, int b) {
            this.a = a;
            this.b = b;
        }
 
        public int getA() {
            return this.a;
        }
 
        public int getB() {
            return this.b;
        }
 
        @Override
        public String toString() {
            return String.format("{a=%d,b=%d}", this.a, this.b);
        }
 
        @Override
        public int compareTo(A o) {
            if (this.a > o.a) {
                return 1;
            } else if (this.a < o.b) {
                return -1;
            } else {
                if (this.b > o.b) {
                    return 1;
                } else if (this.b < o.b) {
                    return -1;
                } else {
                    return 0;
                }
            }
        }
    }
 
    enum AFunctions implements Function<A, Integer> {
        GET_A {
 
            @Override
            public Integer apply(A arg0) {
                return arg0.getA();
            }
 
        },
 
        GET_B {
 
            @Override
            public Integer apply(A arg0) {
                return arg0.getB();
            }
 
        }
    }
 
    public static void main(String[] args) {
        Ordering<A> aOrder =
            Ordering.natural()
                .nullsFirst()
                .onResultOf(AFunctions.GET_A)
                .compound(
                        Ordering
                            .natural()
                            .nullsFirst()
                            .onResultOf(AFunctions.GET_B))
                .nullsFirst()
                .reverse();
 
        List<A> as = Arrays.asList(
                        new A(1,2),
                        null,
                        new A(1,3),
                        new A(2,1),
                        new A(2,3),
                        null);
 
        System.out.println(aOrder.isOrdered(as)); // false
 
        Collections.sort(as, aOrder);
        System.out.println(as); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}, {a=1,b=2}, null, null]
 
        System.out.println(aOrder.isOrdered(as)); // true
 
        A minA = Collections.min(as, aOrder);
        System.out.println(minA); // {a=2,b=3}
 
        A maxA = Collections.max(as, aOrder);
        System.out.println(maxA); // null
 
        List<A> subAList = aOrder.leastOf(as, 3);
        System.out.println(subAList); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}]
    }
 
}

100

101

102

103

104

105

106

107

108

109

import java.util.Arrays;

import java.util.Collections;

import java.util.List;

import com.google.common.base.Function;

import com.google.common.collect.Ordering;

public class TryOrdering {

public static class A implements Comparable<A> {

int a = 1;

int b = 2;

public A(int a, int b) {

this.a = a;

this.b = b;

}

public int getA() {

return this.a;

}

public int getB() {

return this.b;

}

@Override

public String toString() {

return String.format("{a=%d,b=%d}", this.a, this.b);

}

@Override

public int compareTo(A o) {

if (this.a > o.a) {

return 1;

} else if (this.a < o.b) {

return -1;

} else {

if (this.b > o.b) {

return 1;

} else if (this.b < o.b) {

return -1;

} else {

return 0;

}

enum AFunctions implements Function<A, Integer> {

GET_A {

@Override

public Integer apply(A arg0) {

return arg0.getA();

}

GET_B {

@Override

public Integer apply(A arg0) {

return arg0.getB();

}

public static void main(String[] args) {

Ordering<A> aOrder =

Ordering.natural()

.nullsFirst()

.onResultOf(AFunctions.GET_A)

.compound(

Ordering

.natural()

.nullsFirst()

.onResultOf(AFunctions.GET_B))

.nullsFirst()

.reverse();

List<A> as = Arrays.asList(

new A(1,2),

null,

new A(1,3),

new A(2,1),

new A(2,3),

null);

System.out.println(aOrder.isOrdered(as)); // false

Collections.sort(as, aOrder);

System.out.println(as); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}, {a=1,b=2}, null, null]

System.out.println(aOrder.isOrdered(as)); // true

A minA = Collections.min(as, aOrder);

System.out.println(minA); // {a=2,b=3}

A maxA = Collections.max(as, aOrder);

System.out.println(maxA); // null

List<A> subAList = aOrder.leastOf(as, 3);

System.out.println(subAList); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}]

}