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Commons Lang 3 -- Improved and Powerful StringEscapeUtils

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Commons Lang 3 -- Improved and Powerful StringEscapeUtils

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In the first and second parts of this series I talked about some of the new features like enum and concurrency support that have been added in commons-lang 3. In this article, I am going to talk about a new package 'org.apache.commons.lang3.text.translate' which has been added in commons-lang 3. This package is added to fix problems in the design and implementation of the StringEscapeUtils class which exists in versions prior to 3.0. To make it clearer, let's first talk about the purpose of StringEscapeUtils class and the problems it had prior to version 3.

Purpose of StringEscapeUtils

StringEscapeUtils is a utility class which escapes and unescapes String for Java, JavaScript, HTML, XML, and SQL. For example,

      @Test
public void test_StringEscapeUtils() {
assertEquals("\\\\\\n\\t\\r", StringEscapeUtils.escapeJava("\\\n\t\r")); // escapes the Java String
assertEquals("\\\n\t\r",StringEscapeUtils.unescapeJava("\\\\\\n\\t\\r")); //unescapes the Java String
assertEquals("I didn\\'t say \\\"you to run!\\\"",StringEscapeUtils.escapeJavaScript("I didn't say \"you to run!\""));//escapes the Javascript
assertEquals("&lt;xml&gt;", StringEscapeUtils.escapeXml("<xml>"));//escapes the xml
}

 Problems with StringEscapeUtils

There were a lot of problems in the StringEscapeUtils implementation prior to version3. Some of these were:

  • The implementation was not extensible. Let's take an example of escapeJava, suppose we want to add support in the escapeJava method that it should start escaping single quotes. To add such support we would have to change the existing class code and another if condition which if satisfied will escape single quotes. So, the API was breaking the open-closed principle i.e. a class should be open for extension and closed for modification.
  • It was not symmetric i.e. original should be equal to unescape(escape(original))  but it was not the case.
  • StringEscapeUtils.escapeHtml() escapes multibyte characters like Chinese, Japanese etc. Issue 339
    @Test
    public void testEscapeHiragana() {
    // Some random Japanese unicode characters
    String original = "\u304B\u304C\u3068";
    String escaped = StringEscapeUtils.escapeHtml(original);
    assertEquals(original, escaped);
    }
  • StringEscapeUtils.escapeHtml incorrectly converts unicode characters above U+00FFFF into 2 characters. Issue 480
    @Test
    public void testEscapeHtmlHighUnicode() throws java.io.UnsupportedEncodingException {
    byte[] data = new byte[] { (byte) 0xF0, (byte) 0x9D, (byte) 0x8D,(byte) 0xA2 };
    String original = new String(data, "UTF8");
    String escaped = StringEscapeUtils.escapeHtml(original);
    assertEquals(original, escaped);
    }
  • StringEscaper.escapeXml() escapes characters > 0x7f . Issue 66
    @Test
    public void shouldNotEscapeValuesGreaterThan0x7f() {
    assertEquals("XML should not escape >0x7f values", "\u00A1",StringEscapeUtils.escapeXml("\u00A1"));
    }

Solution -- Rewritten StringEscapeUtils

In version 3.0, StringEscapeUtils is completely rewritten to fix all the bugs associated with this class and to provide a way for the user to customize the behavior of its methods. They have moved all the logic present in the StringEscapeUtils to the classes in the package 'org.apache.commons.lang3.text.translate'.

Let's take an example of escapeJava function in StringEscapeUtils, escapeJava function does not contain any business logic, it just calls the translate method on CharSequenceTranslator reference. What they did can be best understood by looking at the code below

public static final CharSequenceTranslator ESCAPE_JAVA = new AggregateTranslator(new LookupTranslator(
new String[][] {
{"\"", "\\\""},
{"\\", "\\\\"},
}),new LookupTranslator(EntityArrays.JAVA_CTRL_CHARS_ESCAPE()),UnicodeEscaper.outsideOf(32, 0x7f));

 and in the escapeJava method

public static final String escapeJava(String input) {
return ESCAPE_JAVA.translate(input);
}

 A constant of type CharSequenceTranslator was assigned an AggregateTranslator object. AggregateTranslator can take an array of translators, and it iterates over each of them. The LookupTranslator replaces the string at zeroth index with the string at the first index. UnicodeEscaper translates values outside the given range to unicode values. As you can see, you can very easily write your own escape methods.  For example, if you want to add the support of escaping &, you can do it like this

public static final CharSequenceTranslator ESCAPE_JAVA =
new LookupTranslator(
new String[][] {
{"\"", "\\\""},
{"\\", "\\\\"},
}).with(new LookupTranslator(
new String[][]{
{"&", "&"},
{"<", "<"}}
)).with(
new LookupTranslator(EntityArrays.JAVA_CTRL_CHARS_ESCAPE())
).with(
UnicodeEscaper.outsideOf(32, 0x7f)
);
StringEscapeUtils.escapeSql has been removed from the API as it was misleading developers to not use PreparedStatement.This method was not of much use as it was only escaping single quotes.

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