diff --git a/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/CookieConfig.java b/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/CookieConfig.java
index 6b726fdc..fb2c4fb8 100644
--- a/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/CookieConfig.java
+++ b/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/CookieConfig.java
@@ -37,6 +37,13 @@
  */
 public class CookieConfig {
 
+    /**
+     * Creates a new CookieConfig instance.
+     */
+    public CookieConfig() {
+        // Default constructor
+    }
+
     private String name;
     private String value;
     private String domain;
diff --git a/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/CredentialsConfig.java b/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/CredentialsConfig.java
index 886d05d1..0e8baee9 100644
--- a/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/CredentialsConfig.java
+++ b/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/CredentialsConfig.java
@@ -37,6 +37,13 @@
  */
 public class CredentialsConfig {
 
+    /**
+     * Creates a new CredentialsConfig instance.
+     */
+    public CredentialsConfig() {
+        // Default constructor
+    }
+
     /**
      * Type of credentials.
      */
diff --git a/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/WebAuthenticationConfig.java b/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/WebAuthenticationConfig.java
index 221f6fb0..9ed68c2a 100644
--- a/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/WebAuthenticationConfig.java
+++ b/fess-crawler/src/main/java/org/codelibs/fess/crawler/client/http/config/WebAuthenticationConfig.java
@@ -48,6 +48,13 @@
  */
 public class WebAuthenticationConfig {
 
+    /**
+     * Creates a new WebAuthenticationConfig instance.
+     */
+    public WebAuthenticationConfig() {
+        // Default constructor
+    }
+
     /**
      * Type of authentication scheme.
      */
diff --git a/fess-crawler/src/main/java/org/codelibs/fess/crawler/extractor/impl/PsExtractor.java b/fess-crawler/src/main/java/org/codelibs/fess/crawler/extractor/impl/PsExtractor.java
index 4cf73d13..a647c83d 100644
--- a/fess-crawler/src/main/java/org/codelibs/fess/crawler/extractor/impl/PsExtractor.java
+++ b/fess-crawler/src/main/java/org/codelibs/fess/crawler/extractor/impl/PsExtractor.java
@@ -99,6 +99,11 @@ public void setEncoding(final String encoding) {
         this.encoding = encoding;
     }
 
+    /**
+     * Extracts readable text from the given PostScript content.
+     * @param psContent the PostScript content to extract text from
+     * @return the extracted text
+     */
     protected String extractText(final String psContent) {
         final List<String> collectedTexts = new ArrayList<>();
         final List<String> stack = new ArrayList<>();
diff --git a/fess-crawler/src/main/java/org/codelibs/fess/crawler/helper/SitemapsHelper.java b/fess-crawler/src/main/java/org/codelibs/fess/crawler/helper/SitemapsHelper.java
index d2dca1dd..974c4c66 100644
--- a/fess-crawler/src/main/java/org/codelibs/fess/crawler/helper/SitemapsHelper.java
+++ b/fess-crawler/src/main/java/org/codelibs/fess/crawler/helper/SitemapsHelper.java
@@ -212,6 +212,7 @@ protected SitemapSet parse(final InputStream in, final boolean recursive, final
     /**
      * Parses a text-based sitemap from the given input stream.
      * @param in the input stream to parse
+     * @param sitemapBaseUrl the base URL used to resolve relative sitemap URLs
      * @return the parsed sitemap set
      */
     protected SitemapSet parseTextSitemaps(final InputStream in, final String sitemapBaseUrl) {
@@ -265,6 +266,7 @@ protected SitemapSet parseTextSitemaps(final InputStream in, final String sitema
     /**
      * Parses an XML sitemap from the given input stream.
      * @param in the input stream to parse
+     * @param sitemapBaseUrl the base URL used to resolve relative sitemap URLs
      * @return the parsed sitemap set
      */
     protected SitemapSet parseXmlSitemaps(final InputStream in, final String sitemapBaseUrl) {
@@ -699,6 +701,7 @@ public SitemapSet getSitemapSet() {
     /**
      * Parses an XML sitemap index from the given input stream.
      * @param in the input stream to parse
+     * @param sitemapBaseUrl the base URL used to resolve relative sitemap URLs
      * @return the parsed sitemap set
      */
     protected SitemapSet parseXmlSitemapsIndex(final InputStream in, final String sitemapBaseUrl) {
@@ -1161,6 +1164,11 @@ protected static class SizeLimitedInputStream extends FilterInputStream {
 
         private long bytesRead;
 
+        /**
+         * Creates a new SizeLimitedInputStream wrapping the given input stream.
+         * @param in the input stream to wrap
+         * @param maxSize the maximum number of bytes allowed to be read
+         */
         protected SizeLimitedInputStream(final InputStream in, final long maxSize) {
             super(in);
             this.maxSize = maxSize;