small refactor/cleanup: 🧹

- use `isEmpty()` for `String` instead of `length() == 0`
- add `@SuppressWarnings("JavadocReference")`/`@SuppressWarnings("JavadocReference")` for expected cases

Author: oldratlee

README.md

@@ -222,7 +222,7 @@ int cachePolicy = DnsCacheManipulator.getDnsCachePolicy();
 DnsCacheManipulator.setDnsCachePolicy(2);
 
 // View the cache time of missed entries(negative entries)
-DnsCacheManipulator.getDnsNegativeCachePolicy()
+DnsCacheManipulator.getDnsNegativeCachePolicy();
 // Set the cache time of missed entries
 DnsCacheManipulator.setDnsNegativeCachePolicy(0);
 ```
@@ -233,7 +233,7 @@ DnsCacheManipulator.setDnsNegativeCachePolicy(0);
 
 With the release of Java 16 the access control of the new Jigsaw module system is starting to be enforced by the JVM. If you use `DCM` under Java 16+, add below Java options:
 
-```java
+```sh
 --add-opens java.base/java.net=ALL-UNNAMED
 --add-opens java.base/sun.net=ALL-UNNAMED
 ```

docs/developer-guide.md

@@ -79,4 +79,4 @@ The LTS `JDK` versions(8/11/17) and recent versions are tested , other `JDK` ver
     - [FileOutput Node - Java DNS caching pitfall - quick clarification and tips](https://www.ibm.com/developerworks/community/blogs/aimsupport/entry/fileoutput_node_dns_caching_pitfall?lang=en)
 - The [`javahost`](https://github.com/tanhaichao/javahost) project of [`@tanhaichao`](https://github.com/tanhaichao) (Thanks for your work!)
     - [the documentation](http://leopard.io/modules/javahost) of the project.
-    - The solution of how to set up Java DNS Cache in this project comes from this project. When I first encountered the host binding problem in the continuous integration project, I also used the project to solve it 👍
+    - The solution of how to set up Java DNS Cache comes from this project. When I first encountered the host binding problem in the continuous integration project, I also used the project to solve it 👍

docs/zh-CN/library.md

@@ -74,7 +74,7 @@ Java Dns Cache Manipulator(DCM) Library
     - 一个`JVM`进程可以对应一套域名绑定，相互之间不影响，可以实现多场景，多域名绑定的需求压测。
 1. 打开`Java`中的`SecurityManager`时（如在`Web`容器`Tomcat`中的`Web`应用），`Java`的`DNS`缺省是不会失效的。
     如果域名绑定的`IP`变了，可以通过这个库重置`DNS`。
-    - 通过[`Java Dns Cache Manipulator Tool`](../tool)设置运行中`JVM DNS Cache`。  
+    - 通过[`Java Dns Cache Manipulator Tool`](../../tool)设置运行中`JVM DNS Cache`。  
         **无需** 应用包含了`Java Dns Cache Manipulator Library`依赖（即`Jar`）。
     - 或通过执行入口调用`Java Dns Cache Manipulator Library`的方法，比如远程调用或是[`jvm-ssh-groovy-shell`](https://github.com/palominolabs/jvm-ssh-groovy-shell)。  
         ***需要*** 应用已经包含了`Java Dns Cache Manipulator Library`依赖（即`Jar`）。
@@ -170,7 +170,7 @@ DnsCacheManipulator.removeDnsCache("aliyun.com");
 ----------------------------------
 
 ```java
-DnsCache dnsCache = DnsCacheManipulator.getWholeDnsCache()
+DnsCache dnsCache = DnsCacheManipulator.getWholeDnsCache();
 System.out.println(dnsCache);
 ```
 
@@ -184,7 +184,7 @@ int cachePolicy = DnsCacheManipulator.getDnsCachePolicy();
 DnsCacheManipulator.setDnsCachePolicy(2);
 
 // 查看未命中条目的缓存时间
-DnsCacheManipulator.getDnsNegativeCachePolicy()
+DnsCacheManipulator.getDnsNegativeCachePolicy();
 // 设置未命中条目的缓存时间
 DnsCacheManipulator.setDnsNegativeCachePolicy(0);
 ```

library/src/main/java/com/alibaba/dcm/DnsCache.java

@@ -55,10 +55,7 @@ public List<DnsCacheEntry> getNegativeCache() {
      */
     @Override
     public String toString() {
-        return "DnsCache{" +
-                "cache=" + cache +
-                ", negativeCache=" + negativeCache +
-                '}';
+        return "DnsCache{cache=" + cache + ", negativeCache=" + negativeCache + '}';
     }
 
     /**

library/src/main/java/com/alibaba/dcm/DnsCacheEntry.java

@@ -91,11 +91,8 @@ public DnsCacheEntry(String host,
     public String toString() {
         final SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ");
 
-        return "DnsCacheEntry{" +
-                "host='" + host + '\'' +
-                ", ips=" + Arrays.toString(ips) +
-                ", expiration=" + dateFormat.format(expiration) +
-                '}';
+        return "DnsCacheEntry{host='" + host + '\'' + ", ips=" + Arrays.toString(ips) +
+                ", expiration=" + dateFormat.format(expiration) + '}';
     }
 
     /**
@@ -120,7 +117,7 @@ public boolean equals(Object o) {
     public int hashCode() {
         int result = host != null ? host.hashCode() : 0;
         result = 31 * result + Arrays.hashCode(ips);
-        result = 31 * result + (int) (expiration ^ (expiration >>> 32));
+        result = 31 * result + Long.hashCode(expiration);
         return result;
     }
 }

library/src/main/java/com/alibaba/dcm/DnsCacheManipulator.java

@@ -31,6 +31,7 @@
  */
 @ParametersAreNonnullByDefault
 @ReturnValuesAreNonnullByDefault
+@SuppressWarnings("JavadocReference")
 public final class DnsCacheManipulator {
     /**
      * Set a <b>never expired</b> dns cache entry.

library/src/main/java/com/alibaba/dcm/agent/DcmAgent.java

@@ -163,7 +163,7 @@ private static boolean isDcmAgentSuppressExceptionStack() {
         if (suppressException == null) return false;
 
         suppressException = suppressException.trim();
-        if (suppressException.length() == 0) return false;
+        if (suppressException.isEmpty()) return false;
 
         return "true".equalsIgnoreCase(suppressException);
     }
@@ -300,7 +300,7 @@ public static List<String> getActionList() {
     @Nullable
     private static String getConfig(@Nonnull String name) {
         String var = System.getenv(name);
-        if (var == null || var.trim().length() == 0) {
+        if (var == null || var.trim().isEmpty()) {
             var = System.getProperty(name);
         }
         return var;

library/src/main/java/com/alibaba/dcm/internal/InetAddressCacheUtilCommons.java

@@ -19,6 +19,7 @@
 @ParametersAreNonnullByDefault
 @ReturnValuesAreNonnullByDefault
 @ApiStatus.Internal
+@SuppressWarnings("JavadocReference")
 public final class InetAddressCacheUtilCommons {
     /**
      * We never really have "never".

library/src/main/java/com/alibaba/dcm/internal/InetAddressCacheUtilForNew.java

@@ -35,6 +35,7 @@
 @ParametersAreNonnullByDefault
 @ReturnValuesAreNonnullByDefault
 @ApiStatus.Internal
+@SuppressWarnings("JavadocReference")
 public final class InetAddressCacheUtilForNew {
     /**
      * {@link InetAddress.CachedAddresses}

library/src/main/java/com/alibaba/dcm/internal/InetAddressCacheUtilForOld.java

@@ -41,6 +41,7 @@
 @ParametersAreNonnullByDefault
 @ReturnValuesAreNonnullByDefault
 @ApiStatus.Internal
+@SuppressWarnings("JavadocReference")
 public final class InetAddressCacheUtilForOld {
     /**
      * Need convert host to lowercase, see {@link InetAddress#cacheAddresses(String, InetAddress[], boolean)}.
@@ -170,6 +171,7 @@ private static Object getNegativeCacheOfInetAddress()
     /**
      * @return {@link InetAddress#addressCache} and {@link InetAddress#negativeCache}
      */
+    @SuppressWarnings("JavaReflectionMemberAccess")
     private static Object[] getAddressCacheAndNegativeCacheOfInetAddress0()
             throws NoSuchFieldException, IllegalAccessException {
         if (ADDRESS_CACHE_AND_NEGATIVE_CACHE != null) return ADDRESS_CACHE_AND_NEGATIVE_CACHE;