Merge pull request #4611 from anuraaga/remove-string-move

[Java] Remove unsafe no-copy String allocation since it's not useful in rece…

java/core/src/main/java/com/google/protobuf/UnsafeUtil.java

@@ -33,7 +33,6 @@ package com.google.protobuf;
 import java.lang.reflect.Field;
 import java.nio.Buffer;
 import java.nio.ByteBuffer;
-import java.nio.ByteOrder;
 import java.security.AccessController;
 import java.security.PrivilegedExceptionAction;
 import java.util.logging.Level;
@@ -72,8 +71,6 @@ final class UnsafeUtil {
 
   private static final long BUFFER_ADDRESS_OFFSET = fieldOffset(bufferAddressField());
 
-  private static final long STRING_VALUE_OFFSET = fieldOffset(stringValueField());
-
   private UnsafeUtil() {}
 
   static boolean hasUnsafeArrayOperations() {
@@ -149,10 +146,6 @@ final class UnsafeUtil {
     return MEMORY_ACCESSOR.getObject(target, offset);
   }
 
-  static void putObject(Object target, long offset, Object value) {
-    MEMORY_ACCESSOR.putObject(target, offset, value);
-  }
-
   static byte getByte(byte[] target, long index) {
     return MEMORY_ACCESSOR.getByte(target, BYTE_ARRAY_BASE_OFFSET + index);
   }
@@ -262,26 +255,6 @@ final class UnsafeUtil {
     return MEMORY_ACCESSOR.getLong(buffer, BUFFER_ADDRESS_OFFSET);
   }
 
-  /**
-   * Returns a new {@link String} backed by the given {@code chars}. The char array should not
-   * be mutated any more after calling this function.
-   */
-  static String moveToString(char[] chars) {
-    if (STRING_VALUE_OFFSET == -1) {
-      // In the off-chance that this JDK does not implement String as we'd expect, just do a copy.
-      return new String(chars);
-    }
-    final String str;
-    try {
-      str = (String) UNSAFE.allocateInstance(String.class);
-    } catch (InstantiationException e) {
-      // This should never happen, but return a copy as a fallback just in case.
-      return new String(chars);
-    }
-    putObject(str, STRING_VALUE_OFFSET, chars);
-    return str;
-  }
-
   static Object getStaticObject(Field field) {
     return MEMORY_ACCESSOR.getStaticObject(field);
   }

java/core/src/main/java/com/google/protobuf/Utf8.java

@@ -1474,10 +1474,7 @@ final class Utf8 {
         }
       }
 
-      if (resultPos < resultArr.length) {
-        resultArr = Arrays.copyOf(resultArr, resultPos);
-      }
-      return UnsafeUtil.moveToString(resultArr);
+      return new String(resultArr, 0, resultPos);
     }
 
     @Override
@@ -1553,10 +1550,7 @@ final class Utf8 {
         }
       }
 
-      if (resultPos < resultArr.length) {
-        resultArr = Arrays.copyOf(resultArr, resultPos);
-      }
-      return UnsafeUtil.moveToString(resultArr);
+      return new String(resultArr, 0, resultPos);
     }
 
     @Override