Question

Java中+=

Java中 +=是什么意思 什么情况下用

Answer 1

/**
* 通过命名空间方式获取sql
* @param sqlSessionFactory
* @param namespace
* @param params
* @return
*/
public static String getNamespaceSql(SqlSessionFactory sqlSessionFactory, String namespace, Object params) {
params = wrapCollection(params);
Configuration configuration = sqlSessionFactory.getConfiguration();
MappedStatement mappedStatement = configuration.getMappedStatement(namespace);
TypeHandlerRegistry typeHandlerRegistry = mappedStatement.getConfiguration().getTypeHandlerRegistry();
BoundSql boundSql = mappedStatement.getBoundSql(params);
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
StringBuilder sqlStringBuilder = new StringBuilder(boundSql.getSql().replaceAll("\n", "")); if (params != null && parameterMappings != null && parameterMappings.size() > 0) { for (ParameterMapping parameterMapping : parameterMappings) { if (parameterMapping.getMode() != ParameterMode.OUT) {
Object value;
String propertyName = parameterMapping.getProperty(); if (boundSql.hasAdditionalParameter(propertyName)) {
value = boundSql.getAdditionalParameter(propertyName);
} else if (typeHandlerRegistry.hasTypeHandler(params.getClass())) {
value = params;
} else {
MetaObject metaObject = configuration.newMetaObject(params);
value = metaObject.getValue(propertyName);
}
JdbcType jdbcType = parameterMapping.getJdbcType(); if (jdbcType == null) {
jdbcType = VARCHAR;
}
replaceParameter(sqlStringBuilder, value, jdbcType);
}
}
} return sqlStringBuilder.toString();
} /**
* 根据类型替换参数
* 仅作为数字和字符串两种类型进行处理，需要特殊处理的可以继续完善这里
*
* @param sqlStringBuilder
* @param value
* @param jdbcType
* @return
*/
private static void replaceParameter(StringBuilder sqlStringBuilder, Object value, JdbcType jdbcType) { if (value == null) { return;
}

String strValue = String.valueOf(value); switch (jdbcType) { //数字
case BIT: break; case TINYINT: break; case SMALLINT: break; case INTEGER: break; case BIGINT: break; case FLOAT: break; case REAL: break; case DOUBLE: break; case NUMERIC: break; case DECIMAL: break; //其他，包含字符串和其他特殊类型，加单引号
default:
strValue = "'" + strValue + "'";
} int index = sqlStringBuilder.indexOf("?");
sqlStringBuilder.replace(index, index+1, strValue);
} /**
* 简单包装参数
*
* @param object
* @return
*/
private static Object wrapCollection(final Object object) { if (object instanceof List) {
Map<String, Object> map = new HashMap<>();
map.put("list", object); return map;
} else if (object != null && object.getClass().isArray()) {
Map<String, Object> map = new HashMap<>();
map.put("array", object); return map;
} return object;
}

Answer 2

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