Merge pull request #3176 from feg545/v5-dev

增加按字节长度截断字符串方法

hutool-core/src/main/java/cn/hutool/core/util/StrUtil.java

@@ -1,17 +1,21 @@
 package cn.hutool.core.util;
 
+import java.io.StringReader;
+import java.io.StringWriter;
+import java.nio.ByteBuffer;
+import java.nio.CharBuffer;
+import java.nio.charset.Charset;
+import java.nio.charset.CharsetDecoder;
+import java.nio.charset.CodingErrorAction;
+import java.nio.charset.StandardCharsets;
+import java.util.Map;
+
 import cn.hutool.core.text.CharSequenceUtil;
 import cn.hutool.core.text.StrBuilder;
 import cn.hutool.core.text.StrFormatter;
 import cn.hutool.core.text.StrPool;
 import cn.hutool.core.text.TextSimilarity;
 
-import java.io.StringReader;
-import java.io.StringWriter;
-import java.nio.ByteBuffer;
-import java.nio.charset.Charset;
-import java.util.Map;
-
 /**
  * 字符串工具类
  *
@@ -265,8 +269,8 @@ public class StrUtil extends CharSequenceUtil implements StrPool {
 	 *
 	 * @param obj 对象
 	 * @return 字符串
-	 * @since 4.1.3
 	 * @see String#valueOf(Object)
+	 * @since 4.1.3
 	 */
 	public static String toString(Object obj) {
 		return String.valueOf(obj);
@@ -468,4 +472,73 @@ public class StrUtil extends CharSequenceUtil implements StrPool {
 	public static String format(CharSequence template, Map<?, ?> map, boolean ignoreNull) {
 		return StrFormatter.format(template, map, ignoreNull);
 	}
+
+	/**
+	 * 截断字符串，使用其按照UTF-8编码为字节后不超过maxBytes长度。截断后自动追加省略号(...)
+	 * 用于存储数据库varchar且编码为UTF-8的字段
+	 *
+	 * @param str      java字符串
+	 * @param maxBytes 最大字节长度
+	 * @return 截断后的字符
+	 */
+	public static String truncateUtf8(String str, int maxBytes) {
+		Charset charset = StandardCharsets.UTF_8;
+		//UTF-8编码单个字符最大长度4
+		return truncateByByteLength(str, charset, maxBytes, 4, true);
+	}
+
+	/**
+	 * 截断字符串，使用其按照GB18030编码为字节后不超过maxBytes长度。截断后自动追加省略号(...)
+	 * 用于存储数据库varchar且编码为GB2312，GBK，GB18030的字段
+	 *
+	 * @param str
+	 * @param maxBytes
+	 * @return
+	 */
+	public static String truncateGb18030(String str, int maxBytes) {
+		Charset charset = Charset.forName("GB18030");
+		//GB18030编码单个字符最大长度2
+		return truncateByByteLength(str, charset, maxBytes, 2, true);
+	}
+
+	/**
+	 * 截断字符串，使用其按照指定编码为字节后不超过maxBytes长度
+	 *
+	 * @param str        原始字符串
+	 * @param charset    指定编码
+	 * @param maxBytes   最大字节数
+	 * @param factor     速算因子，取该编码下单个字符的最大可能字节数
+	 * @param appendDots 截断后是否追加省略号(...)
+	 * @return
+	 */
+	public static String truncateByByteLength(String str, Charset charset, int maxBytes, int factor,
+			boolean appendDots) {
+		//字符数*速算因子<=最大字节数
+		if (str == null || str.length() * factor <= maxBytes) {
+			return str;
+		}
+		byte[] sba = str.getBytes(charset);
+		if (sba.length <= maxBytes) {
+			return str;
+		}
+		//限制字节数
+		int limitBytes;
+		if (appendDots) {
+			limitBytes = maxBytes - "...".getBytes(charset).length;
+		} else {
+			limitBytes = maxBytes;
+		}
+		ByteBuffer bb = ByteBuffer.wrap(sba, 0, limitBytes);
+		CharBuffer cb = CharBuffer.allocate(limitBytes);
+		CharsetDecoder decoder = charset.newDecoder();
+		//忽略被截断的字符
+		decoder.onMalformedInput(CodingErrorAction.IGNORE);
+		decoder.decode(bb, cb, true);
+		decoder.flush(cb);
+		String result = new String(cb.array(), 0, cb.position());
+		if (appendDots) {
+			return result + "...";
+		}
+		return result;
+	}
 }

hutool-core/src/test/java/cn/hutool/core/util/StrUtilTest.java

@@ -1,11 +1,12 @@
 package cn.hutool.core.util;
 
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+
 import cn.hutool.core.lang.Dict;
 import org.junit.Assert;
 import org.junit.Test;
 
-import java.util.List;
-
 /**
  * 字符串工具类单元测试
  *
@@ -648,4 +649,43 @@ public class StrUtilTest {
 		final String result = StrUtil.indexedFormat(template, 10);
 		Assert.assertEquals("I'm 10 years old.", result);
 	}
+
+	@Test
+	public void truncateUtf8Test() {
+		String str = "这是This一段中英文";
+		String ret = StrUtil.truncateUtf8(str, 12);
+		Assert.assertEquals("这是Thi...", ret);
+
+		ret = StrUtil.truncateUtf8(str, 13);
+		Assert.assertEquals("这是This...", ret);
+
+		ret = StrUtil.truncateUtf8(str, 14);
+		Assert.assertEquals("这是This...", ret);
+
+		ret = StrUtil.truncateUtf8(str, 999);
+		Assert.assertEquals(str, ret);
+	}
+
+	@Test
+	public void truncateGb18030Test() {
+		String str = "这是This一段中英文";
+		String ret = StrUtil.truncateGb18030(str, 12);
+		Assert.assertEquals("这是This...", ret);
+
+		ret = StrUtil.truncateGb18030(str, 13);
+		Assert.assertEquals("这是This一...", ret);
+
+		ret = StrUtil.truncateGb18030(str, 14);
+		Assert.assertEquals("这是This一...", ret);
+
+		ret = StrUtil.truncateGb18030(str, 999);
+		Assert.assertEquals(str, ret);
+	}
+
+	@Test
+	public void truncateByByteLengthTest() {
+		String str = "This is English";
+		String ret = StrUtil.truncateByByteLength(str, StandardCharsets.ISO_8859_1,10, 1, false);
+		Assert.assertEquals("This is En", ret);
+	}
 }