diff --git a/cpp/src/common/allocator/byte_stream.h b/cpp/src/common/allocator/byte_stream.h
index 15f15b798d..a56c2b5916 100644
--- a/cpp/src/common/allocator/byte_stream.h
+++ b/cpp/src/common/allocator/byte_stream.h
@@ -1280,7 +1280,7 @@ class SerializationUtil {
             } else if (len != read_len) {
                 ret = E_BUF_NOT_ENOUGH;
             } else {
-                str = std::string(tmp_buf);
+                str.assign(tmp_buf, len);
             }
             mem_free(tmp_buf);
         }
diff --git a/cpp/test/common/allocator/byte_stream_test.cc b/cpp/test/common/allocator/byte_stream_test.cc
index 3f57cbf84f..dde40fba42 100644
--- a/cpp/test/common/allocator/byte_stream_test.cc
+++ b/cpp/test/common/allocator/byte_stream_test.cc
@@ -22,6 +22,8 @@
 
 #include <cstdint>
 #include <cstring>
+#include <string>
+#include <vector>
 
 namespace common {
 
@@ -66,6 +68,21 @@ class ByteStreamTest : public ::testing::Test {
     ByteStream* byte_stream_;
 };
 
+TEST_F(ByteStreamTest, VarStringPreservesEmbeddedNulls) {
+    const std::vector<std::string> values = {
+        "", std::string("\0", 1), std::string("a\0b", 3),
+        std::string("\0\1\xff\x7f", 4), std::string("tail\0", 5)};
+    for (const auto& value : values) {
+        ASSERT_EQ(SerializationUtil::write_var_str(value, *byte_stream_), E_OK);
+    }
+    for (const auto& expected : values) {
+        std::string actual = "previous value";
+        ASSERT_EQ(SerializationUtil::read_var_str(actual, *byte_stream_), E_OK);
+        ASSERT_EQ(actual, expected);
+    }
+    ASSERT_EQ(byte_stream_->remaining_size(), 0);
+}
+
 TEST_F(ByteStreamTest, WriteReadTest) {
     const uint8_t data[] = {0x01, 0x02, 0x03};
     const uint32_t data_size = sizeof(data);
diff --git a/cpp/test/encoding/dictionary_codec_test.cc b/cpp/test/encoding/dictionary_codec_test.cc
index f9d814cba6..a05090cfa9 100644
--- a/cpp/test/encoding/dictionary_codec_test.cc
+++ b/cpp/test/encoding/dictionary_codec_test.cc
@@ -55,6 +55,50 @@ TEST_F(DictionaryTest, DictionaryEncoder) {
     }
 }
 
+TEST_F(DictionaryTest, ReadJavaBinaryDictionary) {
+    // Java DictionaryEncoder: empty, NUL-prefixed binary, embedded/trailing
+    // NUL, and repeated dictionary entries.
+    const uint8_t java_bytes[] = {8,  0, 8,  0,  1,   255, 127, 6,
+                                  97, 0, 98, 10, 116, 97,  105, 108,
+                                  0,  5, 2,  3,  6,   27,  64};
+    const std::vector<std::string> expected = {"",
+                                               std::string("\0\1\xff\x7f", 4),
+                                               std::string("a\0b", 3),
+                                               std::string("tail\0", 5),
+                                               std::string("\0\1\xff\x7f", 4),
+                                               ""};
+    common::ByteStream stream(16, common::MOD_DICENCODE_OBJ);
+    ASSERT_EQ(stream.write_buf(java_bytes, sizeof(java_bytes)), common::E_OK);
+    DictionaryDecoder decoder;
+    decoder.init();
+    for (const auto& value : expected) {
+        ASSERT_TRUE(decoder.has_next(stream));
+        ASSERT_EQ(decoder.read_string(stream), value);
+    }
+    ASSERT_FALSE(decoder.has_next(stream));
+}
+
+TEST_F(DictionaryTest, DictionaryPreservesBinaryStrings) {
+    const std::vector<std::string> values = {"",
+                                             std::string("\0\1\xff\x7f", 4),
+                                             std::string("a\0b", 3),
+                                             std::string("tail\0", 5),
+                                             std::string("\0\1\xff\x7f", 4),
+                                             ""};
+    DictionaryEncoder encoder;
+    common::ByteStream stream(16, common::MOD_DICENCODE_OBJ);
+    encoder.init();
+    for (const auto& value : values) encoder.encode(value, stream);
+    ASSERT_EQ(encoder.flush(stream), common::E_OK);
+    DictionaryDecoder decoder;
+    decoder.init();
+    for (const auto& expected : values) {
+        ASSERT_TRUE(decoder.has_next(stream));
+        ASSERT_EQ(decoder.read_string(stream), expected);
+    }
+    ASSERT_FALSE(decoder.has_next(stream));
+}
+
 TEST_F(DictionaryTest, DictionaryEncoderAndDecoder) {
     DictionaryEncoder encoder;
     common::ByteStream stream(1024, common::MOD_DICENCODE_OBJ);