在针对Java1.5优雅地降级时,如何引用Java1.6API?
我想使用Java1.6中的类来进行Unicode规范化,但我的代码必须能够在Java1.5上运行 我不介意运行在1.5上的代码是否没有进行规范化,但我不希望它在运行时给出在针对Java1.5优雅地降级时,如何引用Java1.6API?,java,graceful-degradation,Java,Graceful Degradation,我想使用Java1.6中的类来进行Unicode规范化,但我的代码必须能够在Java1.5上运行 我不介意运行在1.5上的代码是否没有进行规范化,但我不希望它在运行时给出NoClassDefFoundErrors或ClassNotFoundExceptions 实现这一目标的最佳方式是什么 public interface NfcNormalizer { public String normalize(String str); } public class IdentityNfcNorma
NoClassDefFoundError
s或ClassNotFoundException
s
实现这一目标的最佳方式是什么
public interface NfcNormalizer
{
public String normalize(String str);
}
public class IdentityNfcNormalizer implements NfcNormalizer
{
public String normalize(String str)
{
return str;
}
}
public class JDK16NfcNormalizer implements NfcNormalizer
{
public String normalize(String str)
{
return Normalizer.normalize(str, Normalizer.Form.NFC);
}
}
在客户端代码中:
NfcNormalizer normalizer;
try
{
normalizer = Class.forName("JDK16NfcNormalizer").newInstance();
}
catch(Exception e)
{
normalizer = new IdentityNfcNormalizer();
}
通常的方法是通过反射,即不直接引用所讨论的类,而是通过编程方式调用它。这允许您在相关代码不存在时优雅地捕获异常,然后忽略它,或者尝试其他方法。反射抛出
ClassNotFoundException
,这是一个很好的正常异常,而不是有点可怕的noclassdefounderror
对于java.text.Normalizer
,这应该很容易,因为它只是几个静态方法,并且很容易通过反射调用
我不介意运行在1.5上的代码是否没有进行规范化,但我不希望它在运行时给出NoClassDefFoundErrors或ClassNotFoundException
如果您想避免反射,实际上可以捕获这些错误
通过这种方式,您可以使用Java6编译器针对闪亮的新类进行编译,并且它仍然可以在Java5上工作(如“不做任何事情,但也不会崩溃”)
您还可以将这两种方法结合起来,检查类是否使用反射存在,以及它是否继续以非反射方式调用它。这就是安德鲁的解决方案所做的
如果您还需要在Java5上编译,那么您需要一直进行反射。我也有同样的需求,因为我们有需要在Java 1.2的所有Java版本上运行的代码,但是有些代码需要利用更新的API(如果有) 在使用反射来获取方法对象并动态调用它们的各种排列之后,我通常选择了包装器样式的方法作为最佳方法(尽管在某些情况下,仅将反射的方法存储为静态方法并调用它会更好—这取决于具体情况) 下面是一个示例“System Utility”类,它在运行早期版本时为Java 5公开了某些较新的API—早期JVM中的Java 6也遵循同样的原则。本例使用单例,但如果底层API需要,可以轻松实例化多个对象 有两类:
- SysUtil
- SysUtil_J5
System.err.println(“不支持的规范化方法(jvm)这是一个老问题,但仍然是实际问题。我发现了一些答案中没有提到的可能性 通常建议使用反射,如其他一些答案所示。但如果您不想让代码变得混乱,可以使用。它包含
com.ibm.icu.text.Normalizer
类和normalize()
方法,这些方法执行与java.text.Normalizer/sun.text.Normalizer.icu库相同的任务(应该有)拥有Normalizer的实现,这样您就可以与库共享您的项目,并且应该是独立于java的。缺点是icu图书馆很大 如果您使用Normalizer类只是为了从字符串中删除重音符号/变音符号,还有另一种方法。您可以使用包含
StringUtils
的方法stripeAccents()
:
Lang3库可能会根据java版本使用反射来调用适当的规范化程序。因此,优点是您的代码中没有反射混乱。这并不能直接回答您的问题,但如果您想在java 5上实现规范化,请使用ICU项目libs:@simonn:See,以获取可能满足您需要的代码。
import java.io.*;
import java.util.*;
/**
* Masks direct use of select system methods to allow transparent use of facilities only
* available in Java 5+ JVM.
*
* Threading Design : [ ] Single Threaded [x] Threadsafe [ ] Immutable [ ] Isolated
*/
public class SysUtil
extends Object
{
/** Package protected to allow subclass SysUtil_J5 to invoke it. */
SysUtil() {
super();
}
// *****************************************************************************
// INSTANCE METHODS - SUBCLASS OVERRIDE REQUIRED
// *****************************************************************************
/** Package protected to allow subclass SysUtil_J5 to override it. */
int availableProcessors() {
return 1;
}
/** Package protected to allow subclass SysUtil_J5 to override it. */
long milliTime() {
return System.currentTimeMillis();
}
/** Package protected to allow subclass SysUtil_J5 to override it. */
long nanoTime() {
return (System.currentTimeMillis()*1000000L);
}
// *****************************************************************************
// STATIC PROPERTIES
// *****************************************************************************
static private final SysUtil INSTANCE;
static {
SysUtil instance=null;
try { instance=(SysUtil)Class.forName("SysUtil_J5").newInstance(); } // can't use new SysUtil_J5() - compiler reports "class file has wrong version 49.0, should be 47.0"
catch(Throwable thr) { instance=new SysUtil(); }
INSTANCE=instance;
}
// *****************************************************************************
// STATIC METHODS
// *****************************************************************************
/**
* Returns the number of processors available to the Java virtual machine.
* <p>
* This value may change during a particular invocation of the virtual machine. Applications that are sensitive to the
* number of available processors should therefore occasionally poll this property and adjust their resource usage
* appropriately.
*/
static public int getAvailableProcessors() {
return INSTANCE.availableProcessors();
}
/**
* Returns the current time in milliseconds.
* <p>
* Note that while the unit of time of the return value is a millisecond, the granularity of the value depends on the
* underlying operating system and may be larger. For example, many operating systems measure time in units of tens of
* milliseconds.
* <p>
* See the description of the class Date for a discussion of slight discrepancies that may arise between "computer time"
* and coordinated universal time (UTC).
* <p>
* @return The difference, measured in milliseconds, between the current time and midnight, January 1, 1970 UTC.
*/
static public long getMilliTime() {
return INSTANCE.milliTime();
}
/**
* Returns the current value of the most precise available system timer, in nanoseconds.
* <p>
* This method can only be used to measure elapsed time and is not related to any other notion of system or wall-clock
* time. The value returned represents nanoseconds since some fixed but arbitrary time (perhaps in the future, so values
* may be negative). This method provides nanosecond precision, but not necessarily nanosecond accuracy. No guarantees
* are made about how frequently values change. Differences in successive calls that span greater than approximately 292
* years (263 nanoseconds) will not accurately compute elapsed time due to numerical overflow.
* <p>
* For example, to measure how long some code takes to execute:
* <p><pre>
* long startTime = SysUtil.getNanoTime();
* // ... the code being measured ...
* long estimatedTime = SysUtil.getNanoTime() - startTime;
* </pre>
* <p>
* @return The current value of the system timer, in nanoseconds.
*/
static public long getNanoTime() {
return INSTANCE.nanoTime();
}
} // END PUBLIC CLASS
import java.util.*;
class SysUtil_J5
extends SysUtil
{
private final Runtime runtime;
SysUtil_J5() {
super();
runtime=Runtime.getRuntime();
}
// *****************************************************************************
// INSTANCE METHODS
// *****************************************************************************
int availableProcessors() {
return runtime.availableProcessors();
}
long milliTime() {
return System.currentTimeMillis();
}
long nanoTime() {
return System.nanoTime();
}
} // END PUBLIC CLASS
String str = "éèà";
try {
Class c = Class.forName("java.text.Normalizer");
Class f = Class.forName("java.text.Normalizer$Form");
Field ff = f.getField("NFD");
Method m = c.getDeclaredMethod("normalize", new Class[]{java.lang.CharSequence.class,f});
temp = (String) m.invoke(null, new Object[]{str,ff.get(null)});
} catch (Throwable e) {
System.err.println("Unsupported Normalisation method (jvm <1.6)");
}
System.out.println(temp+" should produce [eea]");
String noAccentsString = org.apache.commons.lang3.StringUtils.stripAccents(s);