JdbcTemplate使用小结

　　org.springframework.jdbc.core.JdbcTemplate.query(String sql, Object[] args, RowMapper<StaffUnionVO> rowMapper) throws DataAccessException

1.自定义rowMapper

public class StaffUnionVO implements RowMapper<StaffUnionVO>, Serializable {private static final long serialVersionUID = 1544023434308856628L;public StaffUnionVO() {}private String code;// 员工编码private String name;// 员工姓名public String getCode() {return code;}public void setCode(String code) {this.code = code;}public String getName() {return name;}public void setName(String name) {this.name = name;}private boolean isExistColumn(ResultSet rs, String columnName) {try {if (rs.findColumn(columnName) > 0) {return true;}} catch (SQLException e) {return false;}return false;}@Overridepublic StaffUnionVO mapRow(ResultSet rs, int row) throws SQLException {StaffUnionVO vo = new StaffUnionVO();     
　
　　　　if (isExistColumn(rs, "code"))vo.setCode(rs.getString("code"));
　　　　if (isExistColumn(rs, "name"))vo.setName(rs.getString("name"));        
　　
　　　　return vo;}
}

　　示例: List<StaffUnionVO> vos = JdbcTemplate.query(sql, new Object[0], new StaffUnionVO() );

2.使用BeanPropertyRowMapper

public class StaffUnionVO implements Serializable {private static final long serialVersionUID = 1544023434308856628L;public StaffUnionVO() {}private String code;// 员工编码private String name;// 员工姓名public String getCode() {return code;}public void setCode(String code) {this.code = code;}public String getName() {return name;}public void setName(String name) {this.name = name;}
}

　　示例：List<StaffUnionVO> vos = JdbcTemplate.query(sql, new Object[0], BeanPropertyRowMapper.newInstance(StaffUnionVO.class));

　　看一下 BeanPropertyRowMapper.java 的源码，可以学到不少东西。

/*** Eclipse Class Decompiler plugin, copyright (c) 2016 Chen Chao (cnfree2000@hotmail.com) ***/
package org.springframework.jdbc.core;import java.beans.PropertyDescriptor;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.BeanUtils;
import org.springframework.beans.BeanWrapper;
import org.springframework.beans.NotWritablePropertyException;
import org.springframework.beans.PropertyAccessorFactory;
import org.springframework.beans.TypeMismatchException;
import org.springframework.dao.DataRetrievalFailureException;
import org.springframework.dao.InvalidDataAccessApiUsageException;
import org.springframework.jdbc.support.JdbcUtils;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;public class BeanPropertyRowMapper<T> implements RowMapper<T> {protected final Log logger = LogFactory.getLog(super.getClass());private Class<T> mappedClass;private boolean checkFullyPopulated = false;private boolean primitivesDefaultedForNullValue = false;private Map<String, PropertyDescriptor> mappedFields;private Set<String> mappedProperties;public BeanPropertyRowMapper() {}public BeanPropertyRowMapper(Class<T> mappedClass) {initialize(mappedClass);}public BeanPropertyRowMapper(Class<T> mappedClass, boolean checkFullyPopulated) {initialize(mappedClass);this.checkFullyPopulated = checkFullyPopulated;}public void setMappedClass(Class<T> mappedClass) {if (this.mappedClass == null) {initialize(mappedClass);} else if (!(this.mappedClass.equals(mappedClass)))throw new InvalidDataAccessApiUsageException(new StringBuilder().append("The mapped class can not be reassigned to map to ").append(mappedClass).append(" since it is already providing mapping for ").append(this.mappedClass).toString());}protected void initialize(Class<T> mappedClass) {this.mappedClass = mappedClass;this.mappedFields = new HashMap();this.mappedProperties = new HashSet();PropertyDescriptor[] pds = BeanUtils.getPropertyDescriptors(mappedClass);for (PropertyDescriptor pd : pds)if (pd.getWriteMethod() != null) {this.mappedFields.put(pd.getName().toLowerCase(), pd);String underscoredName = underscoreName(pd.getName());if (!(pd.getName().toLowerCase().equals(underscoredName))) {this.mappedFields.put(underscoredName, pd);}this.mappedProperties.add(pd.getName());}}//在大写的字符前加入下滑线private String underscoreName(String name) {if (!(StringUtils.hasLength(name))) {return "";}StringBuilder result = new StringBuilder();result.append(name.substring(0, 1).toLowerCase());for (int i = 1; i < name.length(); ++i) {String s = name.substring(i, i + 1);String slc = s.toLowerCase();if (!(s.equals(slc))) {result.append("_").append(slc);} else {result.append(s);}}return result.toString();}public final Class<T> getMappedClass() {return this.mappedClass;}public void setCheckFullyPopulated(boolean checkFullyPopulated) {this.checkFullyPopulated = checkFullyPopulated;}public boolean isCheckFullyPopulated() {return this.checkFullyPopulated;}public void setPrimitivesDefaultedForNullValue(boolean primitivesDefaultedForNullValue) {this.primitivesDefaultedForNullValue = primitivesDefaultedForNullValue;}public boolean isPrimitivesDefaultedForNullValue() {return this.primitivesDefaultedForNullValue;}public T mapRow(ResultSet rs, int rowNumber) throws SQLException {Assert.state(this.mappedClass != null, "Mapped class was not specified");Object mappedObject = BeanUtils.instantiate(this.mappedClass);BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(mappedObject);initBeanWrapper(bw);ResultSetMetaData rsmd = rs.getMetaData();int columnCount = rsmd.getColumnCount();Set populatedProperties = (isCheckFullyPopulated()) ? new HashSet() : null;//稀少的特性for (int index = 1; index <= columnCount; ++index) {String column = JdbcUtils.lookupColumnName(rsmd, index);PropertyDescriptor pd = (PropertyDescriptor) this.mappedFields.get(column.replaceAll(" ", "").toLowerCase());if (pd == null)continue;try {Object value = getColumnValue(rs, index, pd);if ((this.logger.isDebugEnabled()) && (rowNumber == 0))this.logger.debug(new StringBuilder().append("Mapping column '").append(column).append("' to property '").append(pd.getName()).append("' of type ").append(pd.getPropertyType()).toString());try {bw.setPropertyValue(pd.getName(), value);} catch (TypeMismatchException e) {if ((value == null) && (this.primitivesDefaultedForNullValue)) {this.logger.debug(new StringBuilder().append("Intercepted TypeMismatchException for row ").append(rowNumber).append(" and column '").append(column).append("' with value ").append(value).append(" when setting property '").append(pd.getName()).append("' of type ").append(pd.getPropertyType()).append(" on object: ").append(mappedObject).toString());} else {throw e;}}if (populatedProperties != null) {populatedProperties.add(pd.getName());}} catch (NotWritablePropertyException ex) {throw new DataRetrievalFailureException(new StringBuilder().append("Unable to map column ").append(column).append(" to property ").append(pd.getName()).toString(), ex);}}if ((populatedProperties != null) && (!(populatedProperties.equals(this.mappedProperties)))) {throw new InvalidDataAccessApiUsageException(new StringBuilder().append("Given ResultSet does not contain all fields necessary to populate object of class [").append(this.mappedClass).append("]: ").append(this.mappedProperties).toString());}return mappedObject;}protected void initBeanWrapper(BeanWrapper bw) {}protected Object getColumnValue(ResultSet rs, int index, PropertyDescriptor pd) throws SQLException {return JdbcUtils.getResultSetValue(rs, index, pd.getPropertyType());}public static <T> BeanPropertyRowMapper<T> newInstance(Class<T> mappedClass) {BeanPropertyRowMapper newInstance = new BeanPropertyRowMapper();newInstance.setMappedClass(mappedClass);return newInstance;}
}

　　1.通过PropertyDescriptor反映射调用set和get方法

　　2.HashSet、TreeSet equals方法

　　AbstractSet.java

　　public boolean equals(Object o) {if (o == this)return true;if (!(o instanceof Set))return false;Collection<?> c = (Collection<?>) o;if (c.size() != size())return false;try {return containsAll(c);} catch (ClassCastException unused)   {return false;} catch (NullPointerException unused) {return false;}}