mybatis源码解析三之(xml解析器dom和sax)5

绝地灬酷狼 2023-05-21 07:08 44阅读 0赞

### 文章目录 ###

*  xpath解析xml
 *   *  解析DTD
     *  构造Xpath和document
     *  解析String
     *  解析XNode
 *  对反射支持

# xpath解析xml #

public class XPathParser {
        
    
      private final Document document;
      //是否开启验证
      private boolean validation;
      //加载本地DTD
      private EntityResolver entityResolver;
      //Properties标签定义值
      private Properties variables;
      private XPath xpath;
    }

## 解析DTD ##

spring专栏有自定义命名空间解析,就不阐述了

public class XMLMapperEntityResolver implements EntityResolver {
        
    
      //指定mybatis-config.xml的DTD
      private static final String IBATIS_CONFIG_SYSTEM = "ibatis-3-config.dtd";
      private static final String IBATIS_MAPPER_SYSTEM = "ibatis-3-mapper.dtd";
      private static final String MYBATIS_CONFIG_SYSTEM = "mybatis-3-config.dtd";
      private static final String MYBATIS_MAPPER_SYSTEM = "mybatis-3-mapper.dtd";
    
      //指定dtd位置
      private static final String MYBATIS_CONFIG_DTD = "org/apache/ibatis/builder/xml/mybatis-3-config.dtd";
      private static final String MYBATIS_MAPPER_DTD = "org/apache/ibatis/builder/xml/mybatis-3-mapper.dtd";
     @Override
      public InputSource resolveEntity(String publicId, String systemId) throws SAXException {
        
        try {
        
          if (systemId != null) {
        
            String lowerCaseSystemId = systemId.toLowerCase(Locale.ENGLISH);
            //查找sysId指定的DTD文档,并读取
            if (lowerCaseSystemId.contains(MYBATIS_CONFIG_SYSTEM) || lowerCaseSystemId.contains(IBATIS_CONFIG_SYSTEM)) {
        
              return getInputSource(MYBATIS_CONFIG_DTD, publicId, systemId);
            } else if (lowerCaseSystemId.contains(MYBATIS_MAPPER_SYSTEM) || lowerCaseSystemId.contains(IBATIS_MAPPER_SYSTEM)) {
        
              return getInputSource(MYBATIS_MAPPER_DTD, publicId, systemId);
            }
          }
          return null;
        } catch (Exception e) {
        
          throw new SAXException(e.toString());
        }
      }
      }

## 构造Xpath和document ##

public XPathParser(String xml) {
        
          //构造时,初始化xpath
        commonConstructor(false, null, null);
        this.document = createDocument(new InputSource(new StringReader(xml)));
      }

private void commonConstructor(boolean validation, Properties variables, EntityResolver entityResolver) {
        
        this.validation = validation;
        this.entityResolver = entityResolver;
        this.variables = variables;
        XPathFactory factory = XPathFactory.newInstance();
        this.xpath = factory.newXPath();
      }

private Document createDocument(InputSource inputSource) {
        
        // important: this must only be called AFTER common constructor
        try {
        
    
          DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
          factory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);
          factory.setValidating(validation);
    
          factory.setNamespaceAware(false);
          factory.setIgnoringComments(true);
          factory.setIgnoringElementContentWhitespace(false);
          factory.setCoalescing(false);
          factory.setExpandEntityReferences(true);
    
          DocumentBuilder builder = factory.newDocumentBuilder();
          //设置DTD解析器
          builder.setEntityResolver(entityResolver);
          builder.setErrorHandler(new ErrorHandler() {
        
            @Override
            public void error(SAXParseException exception) throws SAXException {
        
              throw exception;
            }
    
            @Override
            public void fatalError(SAXParseException exception) throws SAXException {
        
              throw exception;
            }
    
            @Override
            public void warning(SAXParseException exception) throws SAXException {
        
              // NOP
            }
          });
          //加载XML
          return builder.parse(inputSource);
        } catch (Exception e) {
        
          throw new BuilderException("Error creating document instance.  Cause: " + e, e);
        }
      }

## 解析String ##

public String evalString(Object root, String expression) {
        
        String result = (String) evaluate(expression, root, XPathConstants.STRING);
        //设置节点默认值
        result = PropertyParser.parse(result, variables);
        return result;
      }

public static String parse(String string, Properties variables) {
        
        VariableTokenHandler handler = new VariableTokenHandler(variables);
        //指定处理的占位符格式为${}
        GenericTokenParser parser = new GenericTokenParser("${", "}", handler);
        return parser.parse(string);
      }

public class GenericTokenParser {
        
    
      //占位符开始标记
      private final String openToken;
      //占位符结束标记
      private final String closeToken;
      //解析占位符
      private final TokenHandler handler;
      
      /**
       * 将text根据前后占位符解析
       * @param text
       * @return
       */
      public String parse(String text) {
        
        if (text == null || text.isEmpty()) {
        
          return "";
        }
        // search open token
        //查找第一个开启占位符位置
        int start = text.indexOf(openToken);
        if (start == -1) {
        
          return text;
        }
        char[] src = text.toCharArray();
        int offset = 0;
        //线程安全,记录占位符的值
        final StringBuilder builder = new StringBuilder();
        StringBuilder expression = null;
        while (start > -1) {
        
          if (start > 0 && src[start - 1] == '\\') {
        
            // this open token is escaped. remove the backslash and continue.
            //遇到转义的开始标记,直接将前面的字符串以及开始标记追加
            builder.append(src, offset, start - offset - 1).append(openToken);
            offset = start + openToken.length();
          } else {
        
            // found open token. let's search close token.
            //查找到开始标记,且未转义
            if (expression == null) {
        
              expression = new StringBuilder();
            } else {
        
              expression.setLength(0);
            }
            //前面字符追加
            builder.append(src, offset, start - offset);
            offset = start + openToken.length();
            //从offset后继续查找结束标记
            int end = text.indexOf(closeToken, offset);
            while (end > -1) {
        
              if (end > offset && src[end - 1] == '\\') {
        
                // this close token is escaped. remove the backslash and continue.
                //处理转义的结束标记
                expression.append(src, offset, end - offset - 1).append(closeToken);
                offset = end + closeToken.length();
                end = text.indexOf(closeToken, offset);
              } else {
        
                //将开始标记和结束标记之间字符添加
                expression.append(src, offset, end - offset);
                break;
              }
            }
            if (end == -1) {
        
              //未找到结束标记
              // close token was not found.
              builder.append(src, start, src.length - start);
              offset = src.length;
            } else {
        
              //将占位符的值交给handler处理,并保存builder
              builder.append(handler.handleToken(expression.toString()));
              offset = end + closeToken.length();
            }
          }
          //移动start
          start = text.indexOf(openToken, offset);
        }
        if (offset < src.length) {
        
          builder.append(src, offset, src.length - offset);
        }
        return builder.toString();
      }
    }

private static class VariableTokenHandler implements TokenHandler {
        
        //Properties标签定义值,用于替换占位符
        private final Properties variables;
        //是否支持占位符中使用默认的功能
        private final boolean enableDefaultValue;
        //指定占位符和默认值之间的分隔符
        private final String defaultValueSeparator;
        
      @Override
        public String handleToken(String content) {
        
          //variables非空
          if (variables != null) {
        
            String key = content;
            //是否支持占位符中使用默认值功能
            if (enableDefaultValue) {
        
              //查找分割符
              final int separatorIndex = content.indexOf(defaultValueSeparator);
              String defaultValue = null;
              if (separatorIndex >= 0) {
        
                //获取占位符名称
                key = content.substring(0, separatorIndex);
                //获取默认值
                defaultValue = content.substring(separatorIndex + defaultValueSeparator.length());
              }
              if (defaultValue != null) {
        
                //查找指定占位符
                return variables.getProperty(key, defaultValue);
              }
            }
            //不支持默认值,则直接找
            if (variables.containsKey(key)) {
        
              return variables.getProperty(key);
            }
          }
          //variables空
          return "${" + content + "}";
        }
    }

## 解析XNode ##

public List<XNode> evalNodes(Object root, String expression) {
        
        //XNode,mybatis实现,封装node
        List<XNode> xnodes = new ArrayList<>();
        NodeList nodes = (NodeList) evaluate(expression, root, XPathConstants.NODESET);
        for (int i = 0; i < nodes.getLength(); i++) {
        
          xnodes.add(new XNode(this, nodes.item(i), variables));
        }
        return xnodes;
      }

public class XNode {
        
    
      //w3c对象
      private final Node node;
      //节点名
      private final String name;
      //节点内容
      private final String body;
      //节点属性集合
      private final Properties attributes;
      //Properties对应配置文件
      private final Properties variables;
      private final XPathParser xpathParser;
    
      public XNode(XPathParser xpathParser, Node node, Properties variables) {
        
        this.xpathParser = xpathParser;
        this.node = node;
        this.name = node.getNodeName();
        this.variables = variables;
        this.attributes = parseAttributes(node);
        this.body = parseBody(node);
      }
    
      private Properties parseAttributes(Node n) {
        
        Properties attributes = new Properties();
        //获取节点的属性集合
        NamedNodeMap attributeNodes = n.getAttributes();
        if (attributeNodes != null) {
        
          for (int i = 0; i < attributeNodes.getLength(); i++) {
        
            Node attribute = attributeNodes.item(i);
            //使用PropertyParser 处理每个属性中的占位符
            String value = PropertyParser.parse(attribute.getNodeValue(), variables);
            attributes.put(attribute.getNodeName(), value);
          }
        }
        return attributes;
      }
    
    
      private String parseBody(Node node) {
        
        String data = getBodyData(node);
        //当前节点不是文本节点
        if (data == null) {
        
          NodeList children = node.getChildNodes();
          for (int i = 0; i < children.getLength(); i++) {
        
            Node child = children.item(i);
            data = getBodyData(child);
            if (data != null) {
        
              break;
            }
          }
        }
        return data;
      }
    
      private String getBodyData(Node child) {
        
        //只处理文本内容
        if (child.getNodeType() == Node.CDATA_SECTION_NODE
            || child.getNodeType() == Node.TEXT_NODE) {
        
          String data = ((CharacterData) child).getData();
          //使用PropertyParser 处理文本节点中的占位符
          data = PropertyParser.parse(data, variables);
          return data;
        }
        return null;
      }
    }

# 对反射支持 #

public class Reflector {
        
      //对应的Class 类型
      private final Class<?> type;
      //可读属性的名称集合，可读属性就是存在相应getter 方法的属性，初始值为空数纽
      private final String[] readablePropertyNames;
      //可写属性的名称集合，可写属性就是存在相应setter 方法的属性，初始值为空数纽
      private final String[] writablePropertyNames;
      //记录了属性相应的setter 方法， key 是属性名称， value 是Invoker 对象
      private final Map<String, Invoker> setMethods = new HashMap<>();
      //属性相应的getter 方法集合， key 是属性名称， value 也是Inv o ker 对象
      private final Map<String, Invoker> getMethods = new HashMap<>();
      //记录了属性相应的setter 方法的参数值类型， ke y 是属性名称， value 是setter 方法的参数类型
      private final Map<String, Class<?>> setTypes = new HashMap<>();
      //记录了属性相应的getter 方法的返回位类型， key 是属性名称， value 是getter 方法的返回位类型
      private final Map<String, Class<?>> getTypes = new HashMap<>();
      //记录了默认构造方法
      private Constructor<?> defaultConstructor;
      //记录了所有属性名称的集合
      private Map<String, String> caseInsensitivePropertyMap = new HashMap<>();
    
      public Reflector(Class<?> clazz) {
        
        type = clazz;
        //查找clazz 的默认构造方法（无参构造方法）
        addDefaultConstructor(clazz);
        //处理clazz 中的getter 方法，填充getMethods 集合和getTypes 集合
        addGetMethods(clazz);
        //处理clazz 中的set ter 方法，填充setMethods 集合和set Types 集合
        addSetMethods(clazz);
        //处理没有g etter I setter 方法的字段
        addFields(clazz);
        //根据getMethodslsetMethods 集合，初始化可读／写属性的名称集合
        readablePropertyNames = getMethods.keySet().toArray(new String[0]);
        writablePropertyNames = setMethods.keySet().toArray(new String[0]);
        //初始化caseinsensitivePropertyMap 集合，其中记录了所有大写格式的属性名称
        for (String propName : readablePropertyNames) {
        
          caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
        }
        for (String propName : writablePropertyNames) {
        
          caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
        }
      }
    
       private void addGetMethods(Class<?> clazz) {
        
        Map<String, List<Method>> conflictingGetters = new HashMap<>();
        //获取指定类以及其父类和接口中定义的方法
        Method[] methods = getClassMethods(clazz);
        //对get方法过滤
        Arrays.stream(methods).filter(m ->
            //JavaBean 中getter 方法的方法名长度大于3 且必须以” get ” 开头
          m.getParameterTypes().length == 0 && PropertyNamer.isGetter(m.getName()))
          .forEach(m ->
              //记录到conflictingGetters集合中
            addMethodConflict(conflictingGetters,
              //获取对应的属性名称
              PropertyNamer.methodToProperty(m.getName()), m));
        //对方法同名返回值不一样的处理
        resolveGetterConflicts(conflictingGetters);
      }
    
     private Method[] getClassMethods(Class<?> clazz) {
        
        //用于记录指定类中定义的全部方法的唯一签名以及对应的Meth od 对象
        Map<String, Method> uniqueMethods = new HashMap<>();
        Class<?> currentClass = clazz;
        while (currentClass != null && currentClass != Object.class) {
        
          //记录currentClass 这个类中定义的全部方法.桥方法除外
          addUniqueMethods(uniqueMethods, currentClass.getDeclaredMethods());
    
          // we also need to look for interface methods -
          // because the class may be abstract
          //记录接口中定义的方法
          Class<?>[] interfaces = currentClass.getInterfaces();
          for (Class<?> anInterface : interfaces) {
        
            addUniqueMethods(uniqueMethods, anInterface.getMethods());
          }
          //获取父类，继续while 循环
          currentClass = currentClass.getSuperclass();
        }
    
        Collection<Method> methods = uniqueMethods.values();
    
        return methods.toArray(new Method[0]);
      }
    
    
      private void addUniqueMethods(Map<String, Method> uniqueMethods, Method[] methods) {
        
        for (Method currentMethod : methods) {
        
          //过滤桥接方法,也就是为了兼容泛型,重新定义了一个方法,调用原来的方法,定位桥
          if (!currentMethod.isBridge()) {
        
          //方法得到的方法签名是全局唯一的，可以作为该方法 的唯一标识
            String signature = getSignature(currentMethod);
            // check to see if the method is already known
            // if it is known, then an extended class must have
            // overridden a method
            //检测是否在子类中已经添加过该方法，如果在子类中已经添加过，无须再向uniqueMethods 集合中添加该方法了
            if (!uniqueMethods.containsKey(signature)) {
        
            //记录该签名和方法的对应关系
              uniqueMethods.put(signature, currentMethod);
            }
          }
        }
      }
    }
    
     private void resolveGetterConflicts(Map<String, List<Method>> conflictingGetters) {
        
        for (Entry<String, List<Method>> entry : conflictingGetters.entrySet()) {
        
          Method winner = null;
          String propName = entry.getKey();
          boolean isAmbiguous = false;
          for (Method candidate : entry.getValue()) {
        
            if (winner == null) {
        
              winner = candidate;
              continue;
            }
            //同一属性名称存在多个getter方法，则需要比较这些getter方法的返回，选择getter方法
            //迭代过程中的临时变量，用于记录迭代到目前为止，最适合作为getter 方法的Method
            Class<?> winnerType = winner.getReturnType();
            Class<?> candidateType = candidate.getReturnType();
            if (candidateType.equals(winnerType)) {
        
              //对boolean处理
              if (!boolean.class.equals(candidateType)) {
        
                isAmbiguous = true;
                break;
              } else if (candidate.getName().startsWith("is")) {
        
                winner = candidate;
              }
            } else if (candidateType.isAssignableFrom(winnerType)) {
        
              // OK getter type is descendant
              //当前最适合的方法的返回佳是当前方法返回的子类，什么都不做，当前最适合的方法 依然不变
            } else if (winnerType.isAssignableFrom(candidateType)) {
        
              //当前方法的返回位是当前最适合的方法的返回值的子类，更新临时交量getter，当前的getter 方法成为最适合的getter 方法
              winner = candidate;
            } else {
        
              //返回值相同，二义性，抛出异常
              isAmbiguous = true;
              break;
            }
          }
          //添加到getMethods 集合并填充get Types 集合
          addGetMethod(propName, winner, isAmbiguous);
        }
      }