<h1><strong>Java自定義註解實現網絡訪問重試</strong></h1>
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Retention(RetentionPolicy.RUNTIME)
// 註解會在class中存在,運行時可通過反射獲取
@Target(ElementType.METHOD)
// 目標是方法
@Documented
// 文檔生成時,該註解將被包含在javadoc中,可去掉
public @interface Try {
public int count() default 1;
}
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</pre><pre name="code" class="java">import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
public class JsoupAnn {
// 包裝了下Java基本的方法反射(範圍是帶了我們特定註解的方法)
// 傳入我們要執行的類型,所以我們時常發現某些框架要我們定義好類查找的範圍,或前後綴什麼的
// 可以設置返回值爲空void 或者Object通用,這裏我們爲了測試採用String返回值
public Document parseMethod(Class<?> clazz, String url)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException, SecurityException,
NoSuchMethodException, InstantiationException {
Document doc = null;
// 變量該對象的方法
for (Method method : clazz.getDeclaredMethods()) {
Try t = method.getAnnotation(Try.class);
if (t != null) {
int cnt = 1;
doc = getDoc(url);
while (doc == null && cnt < t.count()) {
System.out.println("--");
doc = getDoc(url);
cnt++;
}
}
}
return doc;
}
private Document getDoc(String url) {
try {
Thread.sleep(1000);
return Jsoup.connect(url).timeout(5000).get();
} catch (Exception e) {
System.out.println("connect timeout!");
}
return null;
}
}
調用
@Try(count=3)
public Document getDocument(String url) {
JsoupAnn ann = new JsoupAnn();
Document doc = null;
try {
doc = ann.parseMethod(JsoupSupport.class, url);
} catch (Exception e) {
</span>}
<span style="white-space:pre"> </span>return doc;
}