补充测试，重构代码

src/main/java/com/alibaba/druid/filter/url/ConnectionConnectFilterChainImpl.java

@@ -13,6 +13,11 @@ import java.sql.Driver;
 import java.sql.SQLException;
 import java.util.Properties;
 
+/**
+ * FilterChain to create new connection with placeholder in URL
+ *
+ * @author DigitalSonic
+ */
 public class ConnectionConnectFilterChainImpl extends FilterChainImpl {
     private final static Log LOG = LogFactory.getLog(ConnectionConnectFilterChainImpl.class);
 

src/main/java/com/alibaba/druid/filter/url/HostAndPortHolder.java

@@ -14,6 +14,11 @@ import java.util.Map;
 import java.util.Properties;
 import java.util.Random;
 
+/**
+ * A singleton object to hold Host & Port information.
+ *
+ * @author DigitalSonic
+ */
 public class HostAndPortHolder {
     private static final Log LOG = LogFactory.getLog(ConnectionConnectFilterChainImpl.class);
 
@@ -30,18 +35,22 @@ public class HostAndPortHolder {
         return instance;
     }
 
-    public static void loadFromProperties(String file) {
+    public static void loadProperties(String file) {
         Properties properties = new Properties();
         if (file == null) {
             return;
         }
-        InputStream is;
+        InputStream is = null;
         try {
             LOG.debug("Trying to load " + file + " from FileSystem.");
             is = new FileInputStream(file);
         } catch(FileNotFoundException e) {
             LOG.debug("Trying to load " + file + " from Classpath.");
-            is = HostAndPortHolder.class.getResourceAsStream(file);
+            try {
+                is = HostAndPortHolder.class.getResourceAsStream(file);
+            } catch (Exception ex) {
+                LOG.warn("Can not load resource " + file, ex);
+            }
         }
         if (is != null) {
             try {

src/main/java/com/alibaba/druid/filter/url/HostAndPortValidatorThread.java

@@ -10,6 +10,12 @@ import java.sql.SQLException;
 import java.util.List;
 import java.util.Properties;
 
+/**
+ * A thread to run the validation on each host:port.
+ * If some host:port is failed in the validation, we can set test flags in DruidDataSource.
+ *
+ * @author DigitalSonic
+ */
 public class HostAndPortValidatorThread implements Runnable {
     private final static Log LOG = LogFactory.getLog(HostAndPortValidatorThread.class);
     private DruidDataSource dataSource;
@@ -38,8 +44,6 @@ public class HostAndPortValidatorThread implements Runnable {
     }
 
     protected void check() {
-        Driver driver = dataSource.getRawDriver();
-        Properties info = dataSource.getConnectProperties();
         String url = dataSource.getRawJdbcUrl();
         if (url == null || (url != null &&
                 (url.indexOf("${") == -1 || url.indexOf("}") == -1))) {
@@ -49,31 +53,40 @@ public class HostAndPortValidatorThread implements Runnable {
         String placeHolder = url.substring(url.indexOf("${") + 2, url.indexOf("}"));
         List<String> values = HostAndPortHolder.getInstance().getAll(placeHolder);
         for (String v : values) {
-            Connection conn = null;
-            try {
-                String realUrl = url.replace("${" + placeHolder + "}", v);
-                conn = driver.connect(realUrl, info);
-                dataSource.validateConnection(conn);
-                HostAndPortHolder.getInstance().removeBlacklist(v);
-            } catch (SQLException e) {
-                LOG.warn("Validation FAILED for " + v, e);
-                HostAndPortHolder.getInstance().addBlacklist(v);
-                modifyFlagsIfNeeded();
-            } finally {
-                if (conn != null) {
-                    try {
-                        conn.close();
-                    } catch (SQLException e) {
-                        LOG.error("Can not close connection for HostAndPort Validation.", e);
-                    }
-                }
-            }
+            validateConnection(dataSource, placeHolder, v);
         }
         if (HostAndPortHolder.getInstance().getBlacklistSize() == 0) {
             resetFlagsIfNeeded();
         }
     }
 
+    private void validateConnection(DruidDataSource dataSource, String placeHolder, String target) {
+        Driver driver = dataSource.getRawDriver();
+        Properties info = dataSource.getConnectProperties();
+        String url = dataSource.getRawJdbcUrl();
+        Connection conn = null;
+
+        try {
+            LOG.debug("Validating " + target + " every " + sleepSeconds + " seconds.");
+            String realUrl = url.replace("${" + placeHolder + "}", target);
+            conn = driver.connect(realUrl, info);
+            dataSource.validateConnection(conn);
+            HostAndPortHolder.getInstance().removeBlacklist(target);
+        } catch (SQLException e) {
+            LOG.warn("Validation FAILED for " + target, e);
+            HostAndPortHolder.getInstance().addBlacklist(target);
+            modifyFlagsIfNeeded();
+        } finally {
+            if (conn != null) {
+                try {
+                    conn.close();
+                } catch (SQLException e) {
+                    LOG.error("Can not close connection for HostAndPort Validation.", e);
+                }
+            }
+        }
+    }
+
     private void resetFlagsIfNeeded() {
         if (modifyTestFlags) {
             dataSource.setTestOnBorrow(oldTestOnBorrow);
@@ -85,7 +98,7 @@ public class HostAndPortValidatorThread implements Runnable {
         if (!modifyTestFlags) {
             return;
         }
-        if (oldTestOnReturn || oldTestOnBorrow) {
+        if (!oldTestOnReturn || !oldTestOnBorrow) {
             dataSource.setTestOnBorrow(true);
             dataSource.setTestOnReturn(true);
         }

src/main/java/com/alibaba/druid/filter/url/JdbcUrlHostAndPortReplaceFilter.java

@@ -11,22 +11,35 @@ import com.alibaba.druid.support.logging.LogFactory;
 import java.sql.SQLException;
 import java.util.Properties;
 
+/**
+ * The filter to replace the placeholder in JDBC URL.
+ *
+ * @author DigitalSonic
+ */
 public class JdbcUrlHostAndPortReplaceFilter extends FilterAdapter {
     private final static Log LOG = LogFactory.getLog(HostAndPortValidatorThread.class);
 
-    public static final String DEFAULT_FILE = "/druid-datasource.properties";
+    public static final String DEFAULT_FILE = "datasource.properties";
 
     private String file = DEFAULT_FILE;
 
     private int healthCheckIntervalSeconds = 0;
     private HostAndPortValidatorThread validatorThread;
+    private Thread runningValidatorThread;
     private boolean isValidatorThreadStarted = false;
+    private boolean modifyTestFlags = false;
 
     public void init() {
         if (file == null || file.trim().length() == 0) {
             file = DEFAULT_FILE;
         }
-        HostAndPortHolder.loadFromProperties(file);
+        HostAndPortHolder.loadProperties(file);
+    }
+
+    public void close() {
+        if (runningValidatorThread != null) {
+            runningValidatorThread.interrupt();
+        }
     }
 
     @Override
@@ -44,9 +57,11 @@ public class JdbcUrlHostAndPortReplaceFilter extends FilterAdapter {
             if (validatorThread == null) {
                 validatorThread = new HostAndPortValidatorThread();
                 validatorThread.setSleepSeconds(healthCheckIntervalSeconds);
+                validatorThread.setModifyTestFlags(modifyTestFlags);
             }
             validatorThread.setDataSource((DruidDataSource) dataSource);
-            new Thread(validatorThread).start();
+            runningValidatorThread = new Thread(validatorThread);
+            runningValidatorThread.start();
             isValidatorThreadStarted = true;
         } else {
             LOG.warn("The DataSource is not a DruidDataSource, ignore HostAndPortValidator.");
@@ -64,4 +79,8 @@ public class JdbcUrlHostAndPortReplaceFilter extends FilterAdapter {
     public void setValidatorThread(HostAndPortValidatorThread validatorThread) {
         this.validatorThread = validatorThread;
     }
+
+    public void setModifyTestFlags(boolean modifyTestFlags) {
+        this.modifyTestFlags = modifyTestFlags;
+    }
 }

src/test/java/com/alibaba/druid/filter/url/HostAndPortHolderTest.java

@@ -7,12 +7,20 @@ import org.junit.Test;
 import java.util.List;
 import java.util.Map;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertTrue;
 
+/**
+ * Test class for HostAndPortHolder
+ *
+ * @author DigitalSonic
+ */
 public class HostAndPortHolderTest {
     @Before
     public void setUp() {
-        HostAndPortHolder.loadFromProperties("/com/alibaba/druid/filter/url/datasource.properties");
+        HostAndPortHolder.loadProperties("/com/alibaba/druid/filter/url/datasource.properties");
     }
 
     @After
@@ -20,6 +28,13 @@ public class HostAndPortHolderTest {
         HostAndPortHolder.getInstance().clearBlacklist();
     }
 
+    @Test
+    public void testLoadFromFileNotExisted() {
+        int size = HostAndPortHolder.getInstance().getHolder().size();
+        HostAndPortHolder.loadProperties("FILE_NOT_FOUND");
+        assertEquals(size, HostAndPortHolder.getInstance().getHolder().size());
+    }
+
     @Test
     public void testLoadFromProperties() {
         Map<String, List<String>> holder = HostAndPortHolder.getInstance().getHolder();

src/test/java/com/alibaba/druid/filter/url/HostAndPortValidatorThreadTest.java

@@ -0,0 +1,40 @@
+package com.alibaba.druid.filter.url;
+
+import com.alibaba.druid.pool.DruidDataSource;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Test class for HostAndPortValidatorThread
+ *
+ * @author DigitalSonic
+ */
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration("classpath:com/alibaba/druid/filter/url/dataSource.xml")
+public class HostAndPortValidatorThreadTest {
+    @Autowired
+    private DruidDataSource dataSource;
+
+    @Test
+    public void testValidateFail() throws Exception {
+        assertEquals(0, HostAndPortHolder.getInstance().getBlacklistSize());
+        dataSource.setValidationQuery("select xxx from foo");
+        Thread.sleep(20 * 1000);
+        assertTrue(HostAndPortHolder.getInstance().getBlacklistSize() > 0);
+        assertTrue(dataSource.isTestOnBorrow());
+        assertTrue(dataSource.isTestOnReturn());
+
+        dataSource.setValidationQuery(null);
+        Thread.sleep(20 * 1000);
+        assertEquals(0, HostAndPortHolder.getInstance().getBlacklistSize());
+        assertFalse(dataSource.isTestOnBorrow());
+        assertFalse(dataSource.isTestOnReturn());
+    }
+}

src/test/java/com/alibaba/druid/filter/url/JdbcUrlHostAndPortReplaceFilterTest.java

@@ -14,8 +14,14 @@ import java.sql.Connection;
 import java.util.ArrayList;
 import java.util.List;
 
-import static org.junit.Assert.*;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
+/**
+ * Test class for JdbcUrlHostAndPortReplaceFilter
+ *
+ * @author DigitalSonic
+ */
 @RunWith(SpringJUnit4ClassRunner.class)
 @ContextConfiguration("classpath:com/alibaba/druid/filter/url/dataSource.xml")
 public class JdbcUrlHostAndPortReplaceFilterTest {
@@ -46,5 +52,4 @@ public class JdbcUrlHostAndPortReplaceFilterTest {
             c.close();
         }
     }
-
 }

src/test/resources/com/alibaba/druid/filter/url/dataSource.xml

@@ -9,8 +9,11 @@
        default-lazy-init="false">
 
     <tx:annotation-driven />
-    <bean id="url-filter" class="com.alibaba.druid.filter.url.JdbcUrlHostAndPortReplaceFilter" init-method="init">
+    <bean id="url-filter" class="com.alibaba.druid.filter.url.JdbcUrlHostAndPortReplaceFilter"
+          init-method="init" destroy-method="close">
         <property name="file" value="/com/alibaba/druid/filter/url/datasource.properties" />
+        <property name="healthCheckIntervalSeconds" value="10" />
+        <property name="modifyTestFlags" value="true" />
     </bean>
 
     <bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource"